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2. KDP SINGLE CRYSTALS
This chapter gives the literature survey of various studies made on KDP single
crystals in the near past.
2.1 Importance
Potassium dihydrogen phosphate (KH2PO4, KDP) is a representative of hydrogen
bonded (hydrogen bond between the phosphate tetrahedral ion) materials which possesses
important piezoelectric, ferroelectric, electro-optic and nonlinear optical properties.
Ferroelectrics with hydrogen bonds, due to relatively high nonlinear efficiency and
dielectric permittivity, huge piezoelectric effect and pyroelectric properties, the
possibility of the spontaneous polarization re-orientation in a relatively small field are
successfully implemented in a wide class of optoelectronic devices and sensor
technology, nonlinear optical and information optical storage, etc. Due to their interesting
electrical and optical properties, structural phase transition (at Curie temperature 123 K),
and ease of crystallization, KDP and its isomorphs have been the subject of a wide
variety of investigations for over 50 years.
A crystallochemical analogue of KDP, NH4H2PO4 (amonium dihydrogen
phosphate, ADP) found fairly wide practical applications and was used as piezoelectric
transducers in microphones, gramophones and other sound reproduction devices. The
very first materials to be used and exploited for their nonlinear optical and electro-optical
properties were KDP and ADP. KDP single crystals have high laser damage threshold,
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large nonlinear optical coefficients, good structural quality and mechanical properties and
they have several device applications. The electro-optic effect of KDP leads to the
application such as polarization filter, electronic light shutter, optical rectifier, electronic
light modulator, piezo optic resonator, transducer, etc [46, 47]. The electro-optic
deflection property of KDP crystals is also used in frequency reformation in neodymium
laser. A tunable ruby laser uses a KDP electro-optical filter of improved design and
construction as a tuning element. The piezo- electric property of KDP crystal makes it
useful for the construction of crystal filters and frequency stabilizers in electronic circuit.
KDP used as a tuning element in laser operation of electro-optic devices is based on the
Pockel‟s effect in which the change in dielectric constant is a linear function of the
applied field [48]. Frequency converters and Pockel‟s cell fabricated from KDP and
DKDP crystals are critical components in fusion class laser system. The acousto-optic
tunable filters have been developed using KDP [49 - 53]. For the inertial confinement
fusion (ICF) experiments, the performance of large aperture switches based on KDP has
been assessed for high power laser experiments [54]. KDP based world‟s largest laser to
generate UV beams has been demonstrated [55]. Using cascaded partially deuterated
KDP crystals the broad band frequency tripling was demonstrated by Wang et al [56].
Rapid growths of large size (40 - 55 cm) KDP crystals as well as rapid growth of KDP
crystals with additives [57] have facilitated to obtain perfect KDP crystals for device
application on large scale.
KDP is an efficient angle-tuned dielectric medium for optical harmonic
generation in and near the visible region [58]. This material offers high transmission
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throughout the visible spectrum and meets the requirements for an optical birefringence
large enough to bracket its refractive index for even the extreme wavelength over which
it is transparent. An additional advantage of KDP is its ability to withstand repeated
exposure to high power density laser radiation without inducing strains and subsequent
inhomogenities in the refractive index [59]. These characteristics make KDP a desirable
material for frequency doubling and mixing experiments with many solid state and dye
lasers with fundamental wavelengths between 1060 and 525 nm.
Huge interest to KDP crystals is caused by their unique physical properties and
high manufacturability. In particular, KDP crystals which possesses extremely high
optical and structural perfection makes it possible to produce elements for doubling and
tripling of laser radiation frequency, electro-optic switches and modulators with an
aperture of several tens and hundreds of square centimeters to be used, e.g. in laser fusion
facilities. These crystals are distinguished by high efficiency of non-linear conversion and
a wide optical transparency range which extends far (up to 1760 nm) to the short-
wavelength region of the spectrum [60].
2.2 Growth of Single Crystals
KDP and its analogous systems such as deuterated KDP (DKDP) and ADP
crystals are of the most widely studied crystals. These crystals have been studied for their
different applications, but also for their morphologies, habits, effect of various growth
parameters, effect of impurities, etc. One of the aims of the researchers all over the world
has been to grow high quality KDP crystals rapidly. For this purpose various authors
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have made various modifications in the growth techniques as well as designed the new
set ups. The high and stable supersaturation of the water-soluble crystal molecule has
been the key issue of realizing the rapid rate of the crystal growth. The crystallization
occurs not only on the crystal surface but also on invisible small crystal cores in the
solution, which causes an undesirable crystal growth in the crystallizer. In 1987, a
splicing technique was reported by Sui et al [61] to speed up the enlargement of the
cross- section of KDP crystals. An n2 (n = 1, 2, 3, 4…) array of (001) oriented seed
crystals were applied to grow KDP crystals up to 72 cm2 in cross-section. The authors
reported the results of a research program concerning the seed splicing technique to grow
large KDP crystal. In 1983 an attempt was made to grow 40 x 40 cm2 cross-section and
100 cm length KDP crystals by Newkirk et al [62]. New technical tasks like high-power
laser systems for nuclear fusion have demand for very large size crystals. Sasaki and
Yokotani [63] have described the growth of huge KDP crystals which have a 40 x 40 cm2
cross section for a frequency converter for high power laser system for nuclear fusion
experiment. They have adopted conventional temperature reduction method (TRM) and
three-vessal method using constant temperature and constant technique. KDP and DKDP
crystals have been grown with the sizes up to 57 x 57 cm2 in cross section and about 55
cm in height by Zaitseva et al [64]. It is also important to control habit during the growth
of KDP crystals to achieve the large size crystal with specific habit for desired
applications. Zaitseva et al [65] proposed certain measures for the habit control. The habit
of solution grown KDP single crystals, space group 42d is formed by a combination of
prismatic {100} and pyramidal {101} faces as shown in Figure 2.1.
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Figure 2.1: Morphology of KDP crystal [66]
Rapid growth of KDP crystals has been obtained by various workers. Linear high
speed growth of 80 mm/day was obtained by computer controlled mechanism by
Minagawa et al [67] and earlier than this a rapid growth of over 50 mm/day was reported
by Nakatsuka et al [68] for KDP crystals. Recently, a movie of KDP crystal growth
weighing 800 pounds is put on internet in Youtube [69], which uses six feet high tank
containing one ton supersaturated solution of KDP. By using the turntable tank to rotate
the crystal it was possible to grow the crystal in two months, otherwise, it would have
taken two years in the conventional technique.
Bespalov et al [70] developed high-rate technique for the growth of KDP crystals
from water solution. Crystals were grown at a rate of 0.5-1 mm/h as compared with a rate
of 0.5-1 mm/day using a conventional technique and measure up to 150x150x80 mm.
Loiacono [71] et al and Bordui et al [72] attained increase in the growth rate of KDP
crystals up to 5 mm per day due to stringent growth conditions by controlling mainly the
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supersaturation using the computer. Fujioka et al [73] developed a set up to grow medium
sized KDP crystal (64x63x43 mm) for one day with a technique achieving higher
supersaturation in the growth solution. Masahiro et al [74] demonstrated KDP single
crystals at the growth rate of 54 mm/day achieving optical quality crystals. Two
important parameters affecting the growth rate and quality of KDP crystals are the pH
and the supersaturation of the solution. Velikhov and Demiraskaya [75] studied the effect
of solution composition on the growth rate of the {100} faces of KDP. Bespalov et al
[76] concentrated their efforts on finding the effect of supersaturation on the growth rate
of the {100} face. Efremova et al [77] reported the macroscopically measured growth rate
of the {100} and {101} faces as a function of pH at a fixed supersaturation. He found that
growth rate of the {100} and {101} faces remain almost constant up to pH of 3.5 beyond
which the growth rate starts to decrease. Zaitseva et al [78] have grown high quality KDP
single crystals of 5-16 cm in size at the growth rate of 10-40 mm/day without
spontaneous nucleation. Kolybaeva et al [79] developed large KDP single crystals with
cross section up to 300x300 mm2 and transmission at the wavelength λ=200 nm of about
86 %.
Impurities are present in all crystallization processes. Usually impurities are
adventitious and undesirable but sometimes they are intentionally added and then they are
called additive. The effect of impurities on the growth rate and habit of crystal growing in
solution has been the subject of many experimental and theoretical studies over many
years. For obtaining large size KDP plate, increasing the growth rate of the crystal is a
vital factor. The use of special additives is an effective way to accelerate the growth rate.
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Usually, different organic/ inorganic compounds are used as additives in industrial
crystallization, and positive effect of some organic additives for the growth of large size
crystals is widely known. In the recent years, efforts have been taken to improve the
quality, growth rate and properties of KDP, by employing new growth techniques [80 –
85, 57]. Podder [86] reported the presence of KCl in the medium is found to suppress the
metal ion impurities to a large extent and increase the growth rate. The increase in the
quality of KDP crystal in the presence of KCl is due to the complexation of trace metal
ion impurities in the solution by Cl- ion. The adjustment effect of additive on the growth
process and properties of crystal has been applied in recent years [87 - 89]. Some papers
[90 - 95] report a contrary effect involving an increase in the growth rate of crystal faces
in the presence of low concentration of additives. Such a growth promoting effect of
additive is called the catalytic effect of additive [94, 95]. The effect is observed in the
presence of organic [88, 90, 92] as well as inorganic additives [82, 92]. Kouji Maeda [96]
reported the growth rate, morphology and impurity dye distribution of faces, {100} and
{101} in KDP crystal due to the addition of organic dyes (sunset yellow, brilliant blue
FCF and sky blue). The growth rate of KDP is reported to increase 6-8 times when grown
from ethylene diamine tetra acetic acid (EDTA) added solution as compared to pure
solution [97].
Several investigators [98 - 102] have used the gel growth technique for growing
perfect and transparent single crystals. Brezina and Havrankova [103] attempted to grow
KDP crystal from agar gel. Later, Joshi and Antony [104] reported the growth of
transparent crystals of KDP in silica gels up to 40x8x7mm3 in size. In a quest to grow the
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long crystals of KDP, the Sankarnarayana – Ramasamy (S-R) method has been employed
by Balamurugan and co-workers [105, 106]. A KDP crystal of 15 mm diameter and 65
mm length has been reported. Furthermore, the feasibility of melt growth methods for
KDP crystals was checked by Pastor and Pastor [107].
2.3 Phase Transition
The potassium dihydrogen phosphate (KDP) crystal exhibits interesting physical
properties such as ferrolectricity and ferroelasticity and it is well known to present a
series of phase transition [108]. In KDP crystals, a decrease in temperature is
accompanied by the ferroelectric phase transition due to proton ordering over the O-
H…O hydrogen bonds. t has been conclusively established that, in the vicinity of the
transition temperature (Tc ≈ 122 K), the protons in this crystal predominantly form
configuration in which two of them are located either at the top of each PO4 tetrahedron
or at its bottom. In this case, one of the occupied proton-lattice modes becomes unstable,
thus giving rise to spontaneous polarization (Ps) along the tetragonal axis c of the crystal.
The oxygen proton configurations formed upon phase transition correspond to the
antiferroelectric-type ordering of dipole moments in the ab plane perpendicular to the
polar axis. Therefore, the phase transition in potassium dihydrogen phosphate can be
considered ferroelectric and antiferroelectric simultaneously [109]. So KDP crystals
represent the most typical hydrogen bonded ferroelectric with the order-disorder phase
transition. KDP exhibit an electric dipole moment even in the absence of external electric
field. It undergoes a phase transition from polarized phase to unpolarised phase. The
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temperature at which the transition takes place is known as the Curie temperature (123
K). KDP has phase transition to ferroelectric from its paraelectric state at 123 K. KDP is
ferroelectric well below room temperature [109]. The low temperature ferroelectric phase
has an orthorhombic unit cell (space group is Fdd2) having the dimensions (at 115 K)
given as a=10.467, b=10.533 and c=6.926 Å [110]. At room temperature KDP is
paraelectric phase has a tetramolecular unit cell (space group is 42d) having the
dimensions given as a=b=7.448 and c=6.977Å [111].
The H- bonded system in KDP and its analogues like ADP and DKDP possessing
continuous three-dimensional H – bond network has been recently studied for proton
transfer along H bonds and to effective anti-coupling of proton that plays the key role on
the ferroelectric behaviour of crystals and discussed by the tunneling parameter (Ω) and
the Ising parameter (Jij ) by Dolin et al [112] and the same is represented in Figure 2.2.
Figure 2.2: H surroundings of PO4 tetrahedron in KDP crystal
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The molecular weight and density at room temperature are respectively 136.09
and 2.33 g/cc [113]. The true melting point of KDP is difficult to determine owing to the
evolution of water vapour and condensation of phosphate species. The reported value is
400 0C [113]. KDP is highly soluble in water and sparingly soluble in alcohol. Above
Curie temperature, Tc (123 K), in the parametric phase transition, the crystal structure of
KDP and deuterated KDP, DKDP (KD2PO4) have been studied by several groups using
X-ray and neutron diffraction [114 - 117]. Below Tc, in the ferroelectric phase, the
accurate crystal structure of DKDP has been reported by Nakano et al [118] using an X-
ray automatic diffractometer. The crystal structure of KDP has been reported by Frazer
and Pepinsky by an X-ray diffraction study in 1953 [115] and by Bacon and Pease by a
neutron diffraction study in 1955 [119] except for the anisotropic temperature factors of
K, P and O atoms. On the basis of the temperature dependence of dielectric constant and
infrared spectra, Ginberg et al [120] observed KDP as ferroelectric phase at 180 0C;
Rapoport [121] found paraelectric phase at 233 0C by differential thermal analysis.
The polymorphism of KDP was reported by Subramony et al [122]. The structural
ordering below Tc in KDP has been studied by using high resolution neutron diffraction
by Nelmes et al [123]. The nature of hydrogen bond and the electron density distribution
in tetragonal KDP at room temperature was obtained by Maximum Entropy Method
(MEM) using the synchrotron radiation X-ray powder diffraction data by Yamamura et al
[124]. Moreover, the synchrotron radiation X – ray multiple diffraction study of KDP
phase transition induced by electric field has been reported by Santosh et al [125]. Xu and
Xue [126] reported the molecular structure of KDP crystal from the chemical bond
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viewpoint. A quantitative study on the structure-property correlation of KDP has been
done on the basis of chemical bond method [127]. The crystallographic structure of KDP
is shown in Figure 2.3, in which important bonds are indicated by lines in Figure 2.4
which give the bond graph of molecules, which clearly shows how constituent atoms are
bonded (including the bonding among the inner and intermolecule).
Figure 2.3: Crystallographic structure of KDP: Hydrogen bonds are indicated
Figure 2.4: Bond graph of KDP molecules
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The hydrogen bonds (dashed lines in Figure: 2.4), which link the neighboring
H2PO4- groups, and the chemical bonds inside H2PO4
- groups (solid lines between P, O
and H atoms in Figure: 2.4), are remarkably similar in these two isomorphs, i.e., the bond
number, length and strength, as well as the bond direction are approximately same..
However, the bond strengths between the adjacent anions (H2PO4-) and cations (K
+) is
significantly different, while the bond number and bond direction are still analogous.
Though there are various kinds of chemical bonds existing in KDP crystals, only the
weaker chemical bonds formed in the crystallization process have a dominant influence
on the crystal growth. When growing crystals in aqueous solution, the constituent atoms
enter into the crystal in the form of fundamental growth units produced by the strong
chemical bonds within them; the bond strength and bond number inside the growth units
are almost invariable in the whole crystallization process. As a constituent part of growth
units, the bond strength inside the growth unit is often stronger but has little influence on
the crystal growth [126].
The effect of doping on crystal structure of KDP and the presence of KDP and
the presence of extra phase can be detected by powder XRD. Podder et al [128] have
investigated lattice distortion in urea and KCl doped KDP crystals, and found that the
structures of the doped crystals were slightly distorted compared to pure KDP crystal.
This might be attributed to strains on the lattice by the absorption of urea and KCl.
Pritula et al [129] studied the effect of urea doping concentration on unit cell parameters
of KDP by powder XRD. To determine the lattice parameters of KDP crystals more
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precisely, the parameter c depending on the concentration of urea in solution has been
measured by the Bond method. The lattice parameter c (Δc = 1.4 x 10-3
) essentially
increased with the addition of 0.2M/2.0M of urea to the solution. At urea concentration
exceeding 0.2M, the observed lattice parameter variation was insignificant. Kumaresan et
al [130] studied the powder XRD patterns of various organic dye (Amaranth, Rhodamine
B and Methyl Orange) doped KDP crystals. Dyes distorted the crystal structure of doped
KDP slightly. This might be due to the strain on the lattice by absorption or substitution
of dyes. Peaks observed in the doped KDP crystals were correlated well with those
observed in individual parent compound with slight shift in the Bragg angle.
Recently, several authors [131 - 135] have reported powder XRD studies of
amino acid doped KDP crystals. All the workers have reported the single phase nature
after doping and shift in the peak positions with change in unit cell parameters.
Gunasekaran and Ramkumar [136] obtained the unit cell parameters of α- histidine doped
KDP crystals and also found less value of axial ratios for doped crystals than the pure
KDP crystal. Kushwaha et al [137] have recently reported the powder XRD pattern of L-
threonine doped KDP crystals and observed a systematic variation in the intensity of
diffraction peaks with varying L-threonine concentration. They did not report any extra
peak due to doping of L-threonine. Also, recently Parikh et al [138] have reported that the
single phase nature of L-alanine doped KDP crystals. Also, L-histidine doped KDP
crystals [135] and L-arginine doped KDP crystals [139] were reported. They reported the
single phase nature and slight change in the unit cell parameters on doping.
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Several other authors studied thermogravimetry of pure KDP crystals [140, 141]
and various doped KDP crystals [54, 142-144]. It has been found that glycine doped KDP
crystal starts decomposing at 204.93 0C and KDP crystal at 207.91
0C [143]. This also
further supports that amino acid doping slightly increases thermal destability and reduces
the phase transition temperature. Moreover, thermal studies on amino acids (L-glutamic
acid, L-histidine and L-valine) doped KDP crystals are reported by Kumaresan [144]
using TGA and DTA. Suresh Kumar and Babu Rajendra [53] found that the doping of L-
arginine, L-histidine and glycine increase the thermal stability of KDP. Delci et al [145]
also reported the thermal stability of the doped crystal is improved than KDP due to the
presence of boron. Deve et al [146] reported the doping with L-threonine made the KDP
crystal comparatively more thermally unstable. Parikh et al [135] have also reported that
when the amount of doping increases the thermal stability decreases as well as the values
of thermodynamic and kinetic parameters decrease.
2.4 Electrical Properties
The dielectric constant is one of the basic electrical properties of solid, which are
correlated with electro-optic property of the crystals [147]. The measurement of dielectric
constant as a function of frequency and temperature is of interest both from theoretical
point of view and from the applied aspects. Essentially, dielectric constant εr is the
measure of how a material is polarized in an external electric field. The dielectric
parameters depend on the frequency of the AC voltage across the material. The electrical
properties of molecules are generally characterized by three quantities:
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(i) Polarizability due to electronic displacement within atoms or ions.
(ii) Polarizability due to atomic or ionic displacement within the molecules. (changes in
bond angles and inter-atomic distances)
(iii) A permanent dipole moment
Electrical conductivity of ionic crystals yields useful information regarding the
mobility and production of lattice defects in these materials. In potassium dihydrogen
phosphate (KDP) type of crystals, the possible type of point defects which help the
electrical conduction process are the ionization defects, viz (HPO4)- and H3PO4 is
produced as a result of proton jump from one phosphate group to another along the same
bond [148]. Electrical conductivity of the KDP group crystal is determined by the proton
transport within the frame work of hydrogen bond [149]. Two mechanisms can be
proposed, which are: (1) considering similarity to the conductivity mechanism in ice
having hydrogen bonds [139, 149-151] and (2) considering conductivity associated with
the incorporation into the crystal lattice of impurities having different valences and the
formation of corresponding defects in the ionic crystals [150]. It has been assumed that
the conductivity of ice is obtained by the simultaneous presence of positive and negative
ions and orientational defects – vacant hydrogen bonds (L-defects) and doubly occupied
hydrogen bonds (D-defects). Other possible defects are vacancies and defect associates
[149].
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The temperature dependence of conductivity has lead Meena and Mahadevan
[139] to consider that the conductivity of KDP crystals can be determined by both
thermally generated L-defects and the foreign impurities incorporated into the lattice and
generating the L-defects there. Lokshin [152] assumed that (HPO4)-2
ions are also
responsible for the formation of vacant hydrogen bonds (L-defects). Therefore, it is easy
to understand from this discussion that the proton transport depends on the generation of
L-defects. The increase of conductivity with increase in temperature for L-arginine doped
KDP and ADP crystals [139] can be due to the interstitials which are expected to be
occupied by L-arginine molecules in KDP. This induces bulk defect states due to
competition in getting the sites for the L-arginine molecules to occupy. The L-arginine
molecules can be added to some extent in addition to the replacement of ions in the KDP
and ADP lattices and creating additional hydrogen bonds. As the conduction in KDP and
ADP occurs through protons and mainly due to the anions (H2PO4)- ions and not due to
the cations (K+, NH4
+), the additional hydrogen bonds created may reduce the L-defects
and consequently obstruct the movement of protons. This is the possible explanation
given by Meena and Mahadevan [139] for the decrease in the conductivity value with
increase in impurity concentration. The addition of L-arginine leads to decrease electrical
parameters such as ζdc, ζac, εr and tanδ for both KDP and ADP crystals, which has lead
Meena and Mahadevan [139] to conclude that L-arginine addition makes possible for the
KDP and ADP crystals to become low εr value dielectrics.
Moreover, the dielectric study of amino acids (L-glutamic acid, L-histidine and L-
valine) doped KDP crystal was carried out by Kumaresan [144, 153]. The authors found
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that on doping of amino acids the value of dielectric constant of KDP crystals decreased
and also decreased with increase in the frequency of applied field. Moreover, Larginine,
L-histidine and glycine doped KDP crystals were grown by Kumar and Babu [154]. They
have studied the dielectric behaviour and found the dielectric constant and dielectric loss
less in doped crystals when compared to pure KDP crystals. The dielectric constant
values were obtained comparatively low for Li+ ion added KDP crystals than the pure
KDP crystals within the frequency range 8 to 12 GHz. This suggested that the Li+
ion
added KDP crystals were more suitable for high speed electro-optic modulation than pure
KDP crystals [155]. Similarly high frequency dielectric study of thiourea doped KDP
crystals was carried out in X-band region of micro-wave frequency by Hussaini et al
[156]. They also found that the dielectric constant of thiourea doped KDP was less than
the pure KDP crystals. Suresh Kumar et al [53] reported the lower value of dielectric
constant due to doping with L-arginine, L-histidine and glycine in KDP crystal.
Earlier reports on KDP crystals doped with oxalate and chloride impurities have
shown increase in conductivity, which has been explained as due to the replacement of
(H2PO4)- ions by (C2O4)
-2 and Cl
- ions [157,158]. It was found that the activation energy
of KDP crystal does not vary much on adding oxalate impurity of various concentrations
[159]. Udupa et al [160] have found for KDP crystals that the dielectric constant
decreases with the increase of temperature at all frequencies studied. The same authors
also have observed the appreciable increase in the value of dielectric constant after
impurity (MgO) addition and decrease in its value with increase in frequency. It has been
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observed that the KDP system has become complex after ion irradiation and it shows
irregular behaviour with regard to conductivity property.
O‟Keeffe and Perrino [161] had measured the electrical conductivity of pure and
found that there is knee point at 180 0C. The activation energies were 0.72 eV and 0.56
eV for the temperature above and below 180 0C respectively. Harris and Vella [149]
measured the DC conductivity, a knee was found in the thermal evalution of conductivity
at 100 0C with the slightly different activation energies of 0.99 and 0.53 eV. Sharon and
Kalia [162] measured the DC conductivity with activation energy of 0.76 eV without any
anomaly in the conductivity plot. The carrier of the electrical conduction in KDP-type
crystals has been proved to be proton by coulomeric determination [163,164].
Various parameters affect the dielectric properties of the materials. Doping of
various impurity ions changes the dielectric of KDP crystal. Ananda Kumari and
Chandramani [165] have studied dielectric properties of Au+
doped/undoped KDP
crystals containing KI/NaI with varying frequency at room temperature. They have found
that the dielectric constant decreases with increase in frequency of applied field. Parikh et
al [166] have grown L-alanine doped KDP crystals. It was found that the dielectric
constant and dielectric loss values of L-alanine doped KDP crystals were lower than that
of pure KDP crystals. Recently, Ambujam [167] studied the effect of cation doping
(Mg2+
, Cu2+
, Ni2+
and Ca2+
) in KDP crystals on their dielectric properties. The variation
of dielectric constant with frequency suggested that as the frequency increased the
dielectric constant decreased and at high frequency the leveling of the plot to the X-axis
was observed.
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Chen et al [168] studied the electrical conduction and dielectric relaxation of KDP
crystals. The author found that the conduction mechanism in KDP crystal is due to the
protonic hopping between hydrogen vacancies at temperatures below 179 0C. Sekar
Ramasubramanian and Mahadevan [169] found that the doping of KCl increases the
dielectric constant with the increase in supersaturation of the solution, from which the
KDP crystal is grown. Deepa et al [170] observed that the impurity (NaCl and NaBr)
reduced the conductivity of KDP crystal. The author found that the non-observance of
systematic variation of conductivity with impurity concentration and impurity addition
due to the complex situation created by the halide impurity ions in the electrical
conduction of KDP crystal. Priya et al [171] have grown pure and impurity (urea and
thiourea) added KDP single crystals and reported the electrical conductivity
measurements along a- and c- directions at various temperatures. Goma et al [172] have
studied the variation of dielectric parameters when urea is added in KDP single crystals.
It was determined that the inclusion of urea leads to the low value of dielectric
permittivity. Balamurugan and Ramasamy [173] found that the dielectric constant was
higher and dielectric loss was less in SR method-grown KDP crystal as against
conventional method grown KDP crystal. The large value of dielectric constant at low
frequency is due to the presence of space charge polarization [174].
2.5 Mechanical Properties
Hardness is one of the important mechanical properties of the materials. The
hardness of a material is defined as the resistance it offers to the motion of dislocations,
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deformation or damage under an applied stress [175]. The most common measurement of
hardness is the indentation type. In order to describe the ISE (Indentation Size Effect) and
RISE (Reverse Indentation Size Effect) behaviours of materials, several models for
relation between applied indentation test load and indentation diagonal length have been
reported in the literature [176]. The hardness test methods used to determine the hardness
consist of indenting a solid surface by a loaded indenter of a definite geometrical shape
and measuring the contact area between the indenter and the material. It is used to
determine the stress needed to produce plastic flow in the brittle material. The ratio of the
load and the contact area is the experimental definition of hardness.
The hardness is not a simple property but rather a complex of mechanical
properties and at the same time a measure of intrinsic bonding of the material [177].
There are clear connections between chemical bonding, hardness and dislocation mobility
[178]. Resistance to the movement of dislocations will determine the hardness of the
materials [179].
Potassium dihydrogen phosphate (KDP) is relatively soft and brittle as compared
to other optical materials, including glasses. Anbukumar et al [180] have measured
Vickers micro-hardness on {100} face of KDP within the load range from 5 to 50 g and
found the variation of hardness from 1.77 to 1.57 GPa. They have also observed that the
indentation increased with increase in applied load. Rao and Sirdeshmukh [181]
measured the Vickers hardness of KDP crystal and reported a Vicker hardness of 1.45
GPa at 200 g. Shaskol‟skaya et al [182] reported measurement of both hardness and
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cracking in the Vickers measurement of KDP and KD2xH2-2xPO4 (deuterated KDP, with
x=0 to 0.95). They used load of 50 to 200 g and reported a hardness reduction from 1.44
to 1.22 GPa as the extent of deuteration x increased from 0 to 0.95. They also measured
the length of crack due to Vickers intents. Marion [183] has reported measured values of
fracture toughness in KDP crystals. Marian apparently used the direct crack method and
reported fracture toughness Kc of 0.2 MPa.m1/2
, as well as 0.09 MPa.m1/2
along the
weakest direction (longest crack). Shanmugham et al [184] observed a value of 187.5
kgmm-2
for the Vickers hardness number of KDP crystal. Joshi and Antony [185] as well
as Joshi et al [186] have studied dependence of hardness on indentation load and
anisotropy of {100} and {011} faces of KDP crystals. They also indicated the presence of
crack patterns around the indentation mark; which were found to be dependent on the
indenter orientation [186].
Micro-hardness studies on {100} face of gel grown KDP and ADP crystals have
been reported by Sengupta and Sengupta [187]. They observed slip lines on the {100}
face of ADP crystal at corners of the impression mark. However, micro-cracks were
observed around the indentation on {100} face of KDP crystals from 10 g load, which
spread out as the load increased. The Vickers micro-hardness decreased as applied load
increased for both crystals and the work hardening coefficient was less than 2, which
indicated the soft material nature. Hardness value of solution grown KDP crystal are less
than that of gel grown KDP crystals [187]. This implies that solution grown crystals are
softer than gel grown crystals which apparently contain more defects. Recently,
Balamurugan and Ramasamy [173] have observed the hardness value for SR method
44
grown crystal which is very much higher (≥ twice) than the hardness of the conventional
method grown crystal. Due to the application of mechanical stress by the indentor,
dislocations are generated locally at the region of indentation. Thus the major
contribution to hardness is attributed to the high stress required for homogeneous
nucleation of dislocation in the small dislocation-free region indented [188]. Larger
hardness value for SR method grown KDP crystals indicates greater stress required to
form dislocation thus confirming greater crystalline perfection.
Further, it has been observed that the hardness value of KDP crystals is greater
than that of ADP crystals [184,187]. This could be attributed to the difference in their
molecular structures. Crystallographically, both ADP and KDP are similar in H2PO4
network. In ADP crystals, N-H…O bond occurs between ammonium and phosphate
groups, whereas KDP structure is a polar structure consisting of K+ and H2PO4
- ions. The
ionic bonding between K+ and H2PO4
- ions is stronger than N-H…O bond existing in
ADP molecules. As a result, KDP shows increased hardness.
The variation of Vickers micro-hardness with load was studied for KDP crystals
grown with organic additives; it was found that the hardness value of KDP is increased
with organic additive via the order urea, thiourea and EDTA respectively [189]. Kannan
et al [50] have studied the influence of La3+
ions on the growth of KDP crystals. They
confirmed by using Vickers micro-hardness that the presence of La3+
ions in the
superfacial crystal growth layers produced weak lattice stress. Recently, Ramakrishna
Murthy and Venkateshwar Rao [190] have reported the study of He+ ion beam
modification of the {100} surfaces of KDP and ADP crystals relative to the as-grown to
45
assess the nature and extent of radiation damage. Moreover, Balamurugan et al [191]
have studied the effect of KCl doping and measured the micro-hardness of KDP crystals.
Rajesh et al [189] have reported that the organic additives improved the
mechanical strength of KDP crystals. Dhanaraj et al [192] found that the hardness value
of potassium thiocyanate doped KDP crystal is lower than that of pure KDP crystal and it
decreases with the increase in dopant concentration. This may be the result of loosely
packed lattice with reduced bond energy due to the introduction of the additive into the
crystal. Here increase in additive (dopant) concentration into parent material leads to the
increase in interatomic distances which results in the diminishing of hardness value with
the additive concentration. Kumaresan et al [193] have reported that the hardness value of
copper thiourea complex doped KDP is less than the other semi-organic crystals.
Rahman and Podder [194] have observed that the hardness and work hardening
coefficient increases with the addition of EDTA in KDP crystal. Jagdish and Rajesh [195]
have grown L-proline doped KDP crystal with improved mechanical hardness. As L-
proline possesses ring structure, which is a stable molecular structure and hence good
mechanical hardness is observed in the doped crystals. Saravanan et al [196] have
reported that the L-arginine doping in KDP crystal improves the hardness. Delci et al
[145] have found that the microhardness value of the pure KDP crystal increases with
doping of boron. This is because of the incorporation of the boron ions into superficial
crystal lattice and removing defect centers which reduce the weak lattice stress on the
surface. Pritula et al [60] have reported room temperature Vickers micro-hardness studies
on {100} and {001} faces of KDP crystals grown from urea doped solutions. They found
46
increase in hardness values for doped crystals compared to pure KDP crystals. Similarly,
Podder [86] earlier concluded in his study that Vicker microhardness exhibited higher
mechanical stability of urea doped crystals than KCl doped.
2.6 Optical Properties
Nonlinear optical (NLO) materials play a vital role in the fabrication of
optoelectronic devices. Recent interest is focused on the development of materials which
have suitable NLO properties for use as the active media in efficient second harmonic
generators, tunable parametric oscillators and broadband electro-optic modulators. In this
regard, a large number of compounds are needed to be screened for NLO applications.
Kurtz and Perry [197] proposed a powder SHG method for comprehensive analysis of the
second order nonlinearity. Employing this technique, Kurtz surveyed a very large number
of compounds. A good NLO crystal should also possess good transmission in ultraviolet
and visible region. It is also important to find the UV cut-off limit for particular crystal.
For this purpose UV-Vis spectroscopy is usually employed.
Traditionally, the materials used to measure second order nonlinear optical
behaviour are inorganic crystals such as lithium niobate (LiNbO3), potassium dihydrogen
phosphate (KDP), ammonium dihydrogen phosphate (ADP), potassium titanyl phosphate
(KTP). KDP is among the most widely used NLO material. It is characterized by good
UV transmission, high damage threshold but still their NLO coefficients are relatively
low. These crystals are distinguished by rather high efficiency of non-linear conversion
and wide optical transparency range which extends far to the short-wavelength region of
47
the spectrum [198]. Various techniques have been employed to study the nonlinear
optical behaviour of KDP crystals. To improve the NLO property of KDP crystal,
researchers have attempted to modify KDP crystal by doping with different type of
impurities. Ganeev et al [199] studied the third order susceptibilities χ(3)
and the non-
linear refractive indices (n2) of KDP at wavelengths 1064 nm and 532 nm by Z-scan
technique. The measurements were carried out at different pulse energies, focusing
conditions and crystal lengths. It was shown by the authors that the increase of phase
matching angle leads to decreasing of χ(3)
of KDP crystals. Also, the self and gross-phase-
modulation coefficients in KDP crystals were measured by the Z-scan technique by
Zheng and Meyerhofer [200].
Guohui et al [57] have grown KCl and EDTA doped KDP crystals by rapid
growth technique. Higher NLO efficiency and laser damage threshold were observed
when the crystals were annealed. Podder [86] observed that the KCl doped KDP crystals
show better non-linear optical properties than the pure KDP crystals. Pure and L-Lysine
doped KDP crystals were grown by Kanagathara and Anbalagan [201]. It was found that
the transmittance percentage is increased for the doped KDP crystals. The effect of
doping of amino acids such as L-glutamic acid, L-valine, L-histidine [144], L-arginine,
L-histidine and glycine [154] in KDP crystals have been reported. Jagdish and Rajesh
[195] have studied the growth of L-proline doped KDP crystals. They found that the
optical transparency increases due to doping and transmittance percentage increases with
the increase in dopant concentration. High conjugation and delocalized π bonding orbitals
of L-proline are responsible for absorption in UV visible region. As the concentration of
48
dopant increases, the zwitter ionic property decreases due to the interaction between
opposite charge ends of L-proline which reduces the delocalized π bonding orbitals. As a
result, the electron jump takes high energy and absorption occurs. Suresh Kumar and
Babu Rajendra [53] have reported that the amino acid doped crystal enhances
transparency and NLO efficiency of KDP crystals.
Lin et al [202] studied the mechanism of the optical behaviour of KDP crystals
theoretically by using the plane wave pseudo-potential total energy software package.
The origin of non-linear effects has been explained through the real space atom cutting
analysis of KDP. In another study, Xue and Zhang [203] have studied the hydrogen
bonds such as O-H---O, N-H---O in KDP and ADP. The second order NLO behaviour of
crystals studied and it is found that hydrogen bonds play very important roles in NLO
contributions to the total nonlinearity.
Mulley et al [134] have studied the growth of L-arginine and L-alanine doped
KDP crystals. Modifications in the lattice parameters and improvement in SHG
efficiency was observed. Parikh et al [166] have investigated the effect of L-alanine on
the growth of KDP crystals. They observed higher SHG efficiency and percentage optical
transmission in KDP crystal by doping with L-alanine, with a slight sacrifice in the UV
cut-off limit. Prasanyaa and Haris [204] have grown L-arginine trifluoroacetate (LATF)
doped KDP single crystals. The enhancement in the transmittance of grown KDP with the
addition of LATF at different ratios was determined by UV-visible spectral analysis.
Suresh Kumar and Babu Rajendra [53] have studied the effect of L-arginine, L-histidine
and glycine on the growth of KDP single crystals. Enhanced SHG efficiency was
49
observed in the case of doped crystals. Pritula et al [129] have investigated the optical
properties of KDP crystals grown from urea doped solutions. It was found that the laser
damage threshold value increases by 25 % on doping. Kumaresan et al [205] have grown
metal ions and dyes doped KDP single crystals. It was observed that dye doping
improves the nonlinear optical properties of the grown crystals. Shirsat et al [54] have
studied the influence of lithium ions on the NLO properties of KDP single crystals.
Enhancement of SHG efficiency after the addition of lithium ions was observed. Delci et
al [145] have reported that the boron addition improves the optical transparency of KDP
crystals.
Rajesh et al [189] have investigated the transmission spectra of pure and organic
additives added KDP crystals. They found that the percentage of transmission has
increased in the order of KDP with urea, KDP with thiourea and KDP with EDTA system
respectively. They also observed that the cut off wavelength is almost the same for pure
and organic additive added KDP crystals. Mulley [206] have found that the transparency
and SHG efficiency of KDP crystal increase by doping with urea phosphate. The increase
in doping level improves the fine cut off at lower wavelength side but no change in the
cut off wavelength has been observed. Dhanaraj et al [85] have studied the potassium
acetate and potassium citrate doped KDP crystals. The optical transparency and SHG
efficiency of KDP crystal are increased by the addition of potassium acetate and
potassium citrate. They have also observed the cut off wavelength is the same for pure
and additive added KDP crystals. The addition of dopants in the optimum condition to
the solution is found to suppress the inclusion and improve the quality of crystals with
50
higher transparency. Kumaresan [207] have investigated the irradiation effect on second
harmonic generation of dyes doped KDP crystals. It has been observed that the NLO
efficiency is increased in dyes doped KDP crystal after irradiation and cut off wave
length is same for pure and dyes doped KDP crystals. The π-conjugation electrons in
dyes after the irradiation alter the lattice orientation in the doped crystal and irradiation
effect diffuses the dyes uniformly in the crystal due to lattice disorder. Kumaresan et al
[193] have observed the transmission is higher for L-valine doped KDP crystals grown at
an optimized pH value of 4.2. They also reported that L-valine doped KDP crystals have
higher NLO efficiency. Akhtar and Podder [208] have reported the enhancement of
optical transmission of L-alanine doped KDP crystals. Dave et al [146] have reported, as
the doping of L-threone increases in KDP crystals, the percentage transmission increases
and the UV cut off frequency are not getting affected due to doping. They have also
found that the SHG efficiency increases due to the doping of L-threone in KDP crystals.
Dhanaraj et al [192] have grown potassium thiocynate added KDP crystals by seed
rotation technique. They observed that the measured SHG efficiency of KSCN added
KDP crystal was 1.31 times that of pure KDP crystal. Neutralization of OH group by
KSCN might be the cause for enhanced NLO property, as electron delocalization to be
much more enhanced than in pure KDP crystal. Saravanan et al [196] have observed a
lower cut off wavelength for L-arginine (235 nm) doped KDP crystal. They also found
the improved SHG efficiency of L-arginine doped KDP crystal. Justin Raj et al [209]
have grown potassium dihydroge phosphate from aqueous solution along {001} plane
with the aid of modified growth assembly of SR method. They have observed the
51
improved transparency of SR method grown KDP crystals than that of conventional
solution grown KDP crystals. Robert et al [210] have also reported the high optical
transparecy of SR method grown KDP crystals.
2.7 Recent Trends in Crystal Growth
The nanocrystals (NCs) are supermolecules with nanometric size, arranged
periodically in three directions of space. The importance of the NCs is that when the
dimensions of crystallites approach the atomic scale, significant changes can occur in the
electronic and the optical properties compared to those of bulk materials [211]. There is a
little research on nanocrystals embedded in crystalline lattices. More recently, a strong
interest has been devoted to NCs of semiconductors embedded in wide gap matrix, such
as glass [212–214] and alkali halide matrices [215–217]. Harada et al [218] fabricated
ZnO NCs embedded in thin alkali halide crystals from their melts. In their PL
measurement, the bound exciton (BE) and free exciton (FE) appeared clearly. The BE
was located at 3.363 eV, the FE appeared at 3.373 eV and the 1 phonon and 2 phonon
replica were observed at 3.32 and 3.25 eV, respectively. However, the authors indicated
that the PL signals have never been detected for the ZnO NCs embedded in bulk alkali
halide matrices grown by usual Bridgeman technique.
Recently, Boudine and his co-workers [219-222] successfully embedded
nanocrystals into the crystalline matrix. Halimi et al [219] have investigated ZnO NCs
embedded in KBr single crystal fabricated by using the Czochralski method. The X-ray
diffraction analysis demonstrated that the KBr cell has not been deformed after the
52
incorporation of ZnO NCs. The optical density measurements indicated a shift of the
absorption edge about 0.71 eV. Moreover, they showed that ZnO NCs present an
intermediate confinement. The study of PL at 1.6 K of ZnO NCs embedded in KBr single
crystal showed that the signals are dominated by the BE exciton lines. This work
indicates that Czochralski method allows the fabrication of semiconductor NCs
embedded in alkali halide matrices with a high crystalline quality. Boudine et al [220]
have elaborated CdS NCs embedded in an NaCl single crystal matrix, performed using
the Czochralski method. They observed that the incorporated CdS is in nanocrystalline
form, as indicated by the optical density spectrum, which exhibits a significant blue shift
of the energy band gap of the CdS NCs. Boudine et al [221] have also successfully grown
CdS nanocrystals (NCs) embedded in bulk KCl single crystal matrix performed using the
Czochralski method. They found the incorporation of CdS NCs with a cubic structure
inside the KCl matrix. The optical density measurements of the CdS NCs embedded in
KCl single crystal show a shift of the absorption edge towards higher energies. The
optical band-gap is estimated to be about 2.60 eV. The photoluminescence (PL) spectrum
of the CdS NCs embedded in KCl single crystal presents four emission bands in the range
of 2.20–2.56 eV. It is useful for NLO applications. Bensouici et al [222] report the
experimental results on the fabrication and optical characterization of Czochralski (Cz)
grown KBr single crystals doped with CdTe crystallites. Optical absorption results
confirm a partial chemical decomposition of CdTe showing two absorption bands at 250
and 585 nm, revealing, respectively, Cd and CdTe incorporation in the KBr lattice.
Photoluminescence spectra at room temperature after annealing show a luminescence
53
band located at 640 nm due to size increasing of CdTe aggregates during temperature
treatment. Balasubramanian et al [223] found that the density and mechanical properties
of TGS crystals were improved by doping water soluble CdS nanoparticle dispersed in
water. They observed the absorption band in the range 490-520 nm in the UV-visible
transmission spectra which indicate the presence of impurity (water soluble CdS) in the
lattice of CdS added TGS crystals.
A promising trend in the development of up-to-date functional optical materials
based on dielectrics is incorporation of nanoparticles into the crystalline matrixes of
traditional nonlinear optical materials, for the improvement of the efficiency of their
nonlinear optical response. Very recently, Pritula and his co-workers [224-230] have
grown KDP crystals doped with TiO2 nanocrystals by the method of temperature
reduction from aqueous solution and studied the effect of titanium dioxide nanoparticles
on the functional properties of KDP single crystals. They found the possibility to grow
KDP single crystals containing incorporated anatase (TiO2) nanocrystals. The KDP single
crystalline matrix was chosen for the TiO2 incorporation under the assumption of:
(1) The possibility to input the anatase nanoparticles into mother liquor at the stage of the
crystal matrix growth;
(2) The possibility of strong coupling of protons, potassium and H2PO43-
ions with active
sites (in particular, with oxygen vacancies) on the surface of the nanoparticles both in the
growth solution and in the crystal matrix;
54
(3) The possibility to control the hydrogen bonds system in the crystalline matrix by
means of photoinduced giant local fields at the TiO2 nanocrystal surface with resonance
excitation of their surface defect states due to the „„soft‟‟ hydrogen bonding structure of
the KDP crystal;
(4) The possibility of the creation and annihilation of pair defects in the KDP crystal due
to reduction–oxidation processes at the nanoparticles surface, i.e. the generation of
hydrogen vacancy and the creation of interstitial hydrogen atom (typical intrinsic
defects).
It has been found that the effect of giant nonlinear optical response of anatase
nanoparticles in KDP crystal matrix substantially depends on the character of
incorporation and distribution of these nanoparticles in the matrix and on the structure
perfection of the matrix itself [224]. They have observed the concentration of the
nanoparticles in the solution does not influence the growth rate of the doped crystals
when the growth is realized under the conditions of natural convection. It is established
that the nanoparticles with adsorbed phosphate-ions are incorporated predominantly into
the pyramidal growth sector of KDP crystals. The process of the growth of TiO2 doped
KDP crystals is that the nanoparticles are rejected by the crystallization front and then
“captured” by the boundaries between the growth layer packets. It was found that the
nanoparticles have no essential influence on the laser damage threshold of KDP with
10-5
wt% [226]. The investigation shows the incorporation of TiO2 nanoparticles slightly
changes the optical quality of KDP crystals and reported the high optical quality crystals
55
with transmittance in the visible range ~90 %, scattering loss < 3 %, and the anomalous
biaxiality value 2V<20' [225]. The presence of TiO2 nanoparticles in the crystal matrix
results in the cubic nonlinear response enhancement and the sign inversion of the
nonlinear refraction index in the intensity range up to 20 MW/cm2 [227]. For the first
time they have obtained the frequency conversion efficiency enhancement in the “thick”
(10 mm) KDP:TiO2 in comparison with KDP crystal due to the internal self-focusing
effect that was observed as the jump beam spatial profile narrowing at moderate peak
intensities up to 100 MW/cm2 [229, 230].
For instance, an attempt [231] was made to design a composite optical material
possessing the properties of both active laser and nonlinear optical media, the
combination “KDP crystal-SiO2 particles” being used as a model system. The influence
of the size of paricles on the probability of their capture was studied, and the growing
crystal was shown to be able to capture effectively 1x10-2
-250 µm SiO2 particles. A study
was performed to prove the possibility of embedding II-VI compound CdTe nanoparticle
in KDP crystalline matrix. They found that CdTe inclusion has been obtained with an
average size of about 24 nm. They observed large blue shift of the band gap of CdTe NCs
from 1.56 eV (bulk) to 2.85 eV (CdTe~2 nm size) which reveals the intrinsic quantum
confinement effect of these nanocrystals [232]. Some of the recent research works done
in the field of nanocrystals embedded in crystalline matrix are listed in Table 2.1.
56
Table 2.1: Recent research work in nanocrystals embedded in crystalline matrix
SI.
No
Title of the work Authors Journal name
1. Structural and optical
properties of CdTe
nanocrystals
embedded in KDP
dielectric crystal
A.Bensouici, J.L.Plaza,
O.Halimi, B.Boudine,
M.Sebais, E.Dieguez
J.Optoelectronics
and Advanced
Materials 10, 2008,
3051-3053.
2. Growth and
characterization of
KDP single crystals
doped with TiO2
nanocrystals
I.Pritula, V.Gayvoronsky,
M.Kopylovsky, M.Kolybaeva,
V.Puzikov. A.Kosinova,
V.Tkachenko, V.Tsurikov ,
T.Konstantiniva, V.Pogibko
Functional Materials
12, 2008, 420-428.
3. Solution growth of
KDP single crystals
doped with titanium
dioxide nanoparticles
I.Pritula, O.Bezkrovnaya,
M.Kolybaeva, A.Kosinova,
D.Sofronov, V.F.Tkachenko,
V.Tsurikov
Materials Chemistry
and Physics 129,
2011, 777-782.
4. Peculiarities of the
growth of KDP single
crystals with
incorporated
aluminium hydroxide
nanoparticles
I.M.Pritula, A.V.Kosinova,
D.A.Vorontsov,M.I.Kolybaeva,
O.N.Bezkrovnaya,
V.F.Tkachenko, O.M.Vovk,
E.V.Grishina
Journal of Crystal
Growth 355, 2012,
26-32.
5. Impact of
incorporated anatase
nanoparticles on the
second harmonic
generation in KDP
single crystals
V.Ya.Gayvoronsky,
M.A.Kopylovsky, M.S.Brodyn,
I.M.Pritula, M.I.Kolybaeva,
V.M.Puzikov
Laser Physics
Letters 10, 2013,
035401(1-5).
57
SI.
No
Title of the work Authors Journal name
6. Optical quality
characterization of
KDP crystals with
incorporated TiO2
nanoparticles and
laser scattering
experiment
simulation
V.Ya.Gayvoronsky,
V.N.Starkov,
M.A.Kopylovsky, M.S.Brodyn,
E.A.Vishnyakov,
A.Yu.Boyarchuk, I.M.Pritula
Ukr. Journal of
Physics 55, 2010,
875-884.
8. Self-focusing effect on
the second harmonic
generation in the
KDP single crystals
with incorporated
anatase nanoparticles
V.Ya.Gayvoronsky,
M.Kopylovsky,V.O.Yatsyna,
A.S.Popov, A.Kosinova,
I.M.Pritula
Functional Material
19, 2012, 54-59.
9. Macroscopic and
microscopic defects
and nonlinear optical
properties of KH2PO4
crystals with
embedded
TiO2nanoparticles
V.G.Grachev, I.A.Vrable,
G.I.Malovichko, I.M.Pritula,
O.N.Bezkrovnaya,
A.V.Kosinova, V.O.Yatsyna,
V.Ya.Gayvoronsky
Journal of Applied
Physics 112, 2012,
014315(1-11)
10. Characterization of
CdS nanocrystals
embedded in KCl
single crystal matrix
by Czochralski
method
B.Boudine, M.Sebais,
O.Halimi, A.Bensouici,
J.L.Plaza, A.Bensouici
Optical Materials
25, 2009, 373-377.
13 Structural and optical
characterization of
ZnO nanocrystals
embedded in bulk
KBr single crystals
O.Halimi, B.Boudine,
M.Sebais, A.Chellouche,
R.Mouras, A.Boudrioua
Material Science
and Engineering,
C23, 2003, 1111-
1114.
58
SI.
No
Title of the work Authors Journal name
11. Structural and optical
properties of CdS
nanocrystals
embedded in NaCl
single crystals
B.Boudine, M.Sebais,
O.Halimi, A.Bensouici,
J.L.Plaza, A.Bensouici
Elsevier Science
Catalysis Today 89,
2004, 293-296.
12. Characterization of
triglycine sulphate
crystals grown in
water-soluble CdS
nanoparticles
dispersed in water
K.Balasubramanian,
P.Selvarajan, E.Kumar
Indian Journal of
Science and
Technology 3, 2010,
41-43.
13 CdTe aggregates in
KBr crystalline
matrix
A.Bensouici, J.L.Plaza,
E.Dieguez, O.Halimi,
B.Boudine, S.Addala,
L.Guerbous, M.Sebais,
Journal of
Luminescence 129,
2009, 948-951.