optical properties of rare earth-activated ca3(po4)2:re
TRANSCRIPT
Optical properties of rare earth-activated Ca3(PO4)2:RE (RE = Eu3+
and Dy3+) phosphors prepared by wet chemical synthesis
S K RAMTEKE1, A N YERPUDE1,* , N S KOKODE2 and S J DHOBLE3
1Department of Physics, N.H. College, Bramhapuri, Chandrapur 441206, India2N.H. College, Bramhapuri, Chandrapur 441206, India3Department of Physics, RTM Nagpur University, Nagpur 440033, India
*Author for correspondence ([email protected])
MS received 2 December 2020; accepted 24 February 2021
Abstract. Optical properties of rare earth-activated Ca3(PO4)2:RE (RE = Eu3? and Dy3?) phosphors obtained by wet
chemical synthesis method, are reported in this paper. The phase confirmation of synthesized phosphor host is done by
X-ray diffraction study. SEM images of the sample host reveal irregular morphology with collection of particles and
porous nature. The crystal structure is not viewed with naked eyes, although particle size ranges from 2–5 micrometres.
Photoluminescence characterization of Ca3(PO4)2:Eu3? gives characteristic orange–red emission at wavelengths of 594,
613 and 617 nm upon near UV excitation at 397 nm attributed to 5D0 ?7F1,
7F2 transition of rare earth Eu3? ion.
Whereas Ca3(PO4)2:Dy3? gives blue–yellow emissions at wavelengths 483 and 574 nm due to near UV excitation at
wavelength of 351 nm, which are corresponding to 4F9/2 ?6H15/2,
6H13/2 transitions of dopant ion Dy3?. Colour
coordinates from CIE diagram of 483 and 574 nm are obtained at (x = 0.0781, y = 0.1704) and (x = 0.471, y = 0.527) for
the Ca3(PO4)2:Dy3? phosphor. Whereas in the case of Ca3(PO4)2:Eu
3? for an emission wavelength of 613 nm, the colour
coordinates are found to be (x = 0.674, y = 0.325). The presented optical investigation of phosphor displays that the
reported phosphor can be a potential contender for ecofriendly solid-state lighting.
Keywords. Phosphate; rare earth; wet chemical method; solid-state lighting.
1. Introduction
In routine occurrence, luminescence materials have enacted
an inestimable position with its utmost accessible application
that is self-lit signalization. This phenomenon indicates the
ability of a material to accumulate energy from (artificial)
lighting, along with visible and ultraviolet (UV) spectrum
close to it and moderately emit it as luminous in the murk at a
normal temperature [1]. Over the previous decade,
advancement in synthesis and characterization of alkaline
earth phosphate phosphors has resulted in significant atten-
tion in this class of materials because solid-state lighting has
many advantages over fluorescent and incandescent lights,
for example, its durability, efficiency and environmentally
friendly characteristics [2–4]. Now, research area including
the white light-emitting diode (wLED) and phosphor con-
verted light emitting diode (pcLED) has become an area of
enormous interest to the researchers all over the world [1–4].
Generally, for the production of white light, a combination of
a blue LED with yellow luminescence from Y3Al5O12:Ce3?
(YAG:Ce3?) phosphor compound is used [5,6].Nevertheless,
white light emission can be obtained usingRGBphosphors by
exciting with near UV chip, which can improve the lumen
output and also enhances colour rendering index (CRI) [7,8].
Recently, it is found that phosphate-based phosphor has
exquisite thermal and hydrolytic stabilities. In particular,
phosphates havingmolecular formula (ABPO4,A = K?, Li?,
Na? and B = Ca2?, Sr2?, Mg2?) materials are found to be
relevant hosts for white light-emitting phosphors [9–11].
Over recent years, several lanthanides activated phosphate-
based phosphors were reported which are useful in wLED
applications [12–15]. Amongst the rare earth elements
available as activators, Eu and Dy are the most commonly
used activators as they give rise to sharp emissions in the
visible blue–green–red region of the electromagnetic spec-
trum [16–19]. Recently, Nagpure et al [20] reported lumi-
nescence properties of phosphate-based Ca3(PO4)2 phosphor
doped with Eu and Dy by solid-state synthesis. Zhang et al[21] reported steep brightness in Eu3?-activated Ca3(PO4)2red phosphor for near UV light emitting diode appliances.
They also prepared the same phosphor with different mor-
phologies by using surfactants and shown that fluorescence
intensity was highly affected by the use of specific surfactants
[22]. Li et al [23] studied the phase transformation obtained
by the controlled quenching and increasing the Eu2? content
in Ca3(PO4)2:Eu2?. They also found that cooling rate
parameter automatically impacts luminescence properties
with improved thermal emission stability. Furthermore,
Bull. Mater. Sci. (2021) 44:174 � Indian Academy of Scienceshttps://doi.org/10.1007/s12034-021-02476-5Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)
tunable blue–green emission was also reported recently in b-Ca3(PO4)2:Eu
2? and Tb3? phosphor due to energy trans-
mission mechanism between the co-dopants, which was
responsible for high quantum efficiency reaching up to 90%
[24]. The phosphate host, Ca3(PO4)2 phosphor has the prop-
erty of heterovalent substitution of Ca2? by various cations to
form the new phases and its copious crystallographic sites for
the doped activator tunable to photoluminescence. Because
of this property, it caughtmuch attention of researchers. Thus,
these phosphors have much ability and potential in the uti-
lization ofwLEDs for their tunable emission. In this paper,we
report the wet chemical synthesis of Ca3(PO4)2:RE3?
(RE3? = Eu3?, Dy3?) phosphors and their photolumines-
cence characterization.
2. Experimental
Both the rare earth-activated phosphate phosphors, Ca3(PO4)2:Eu
3? and Ca3(PO4)2:Dy3? were prepared by wet
chemical method. The doping concentrations of Eu3? and
Dy3? were 1 mol%. For the preparation of Ca3(PO4)2:Eu3?,
calcium nitrate (Ca(NO3)2�6H2O) (analytical reagent (AR)),
ammonium dihydrogen phosphate (NH4H2PO4) (AR) and
europium oxide (Eu2O3) (AR) were used as reactants. The
calcium nitrate and ammonium dihydrogen phosphate were
taken in separate borosil beakers and dissolved in relevant
ratios of distilled water. In a test tube dopant, Eu2O3 was
taken and it dissolved with dilute HNO3. Then, Eu2O3 is
converted to nitrate form. Afterwards, europium nitrate
solutions were then mixed into a beaker and stirred until the
solution becomes transparent. The beaker is then kept on a
magnetic stirrer at 80�C for 10 h. After complete dehy-
dration of the solution mixture, crystalline powder was
obtained as a product. This crystalline powder was taken in
agate mortar and pestle, and grinded to obtain a fine pow-
dered sample. The powder thus obtained was annealed at
800�C for 3 h in a muffle furnace which was then utilized
for further characterization.
3. Results and discussion
3.1 XRD pattern of Ca3(PO4)2 phosphor
X-ray diffraction (XRD) pattern of as-prepared Ca3(PO4)2host is shown in figure 1. The ICCD standard data file no.
861585 is also given for comparison with the obtained XRD
pattern of the prepared compound. The standard data file is
compatible with the sample XRD pattern indicating that the
desired host lattice was obtained from the wet chemical
synthesis. The XRD peaks showed the position of atoms
within lattice structure and crystal size of prepared sample.
From this observation, Ca3(PO4)2 powder was formed with
no impurity phases and implies the accomplish formation of
the homogeneous compound.
3.2 SEM micrographs of Ca3(PO4)2 phosphor
Figure 2 shows SEM images of Ca3(PO4)2 host samples for
two different magnifications. Although the crystal structure
is not visible, morphology and average particle size of the
sample are evident from the SEM imaging. The sample has
an irregular surface structure with a collection of particles.
The porous nature of the sample is visible which may be
due to the evolution of gases during the chemical reaction.
The size of the particles is in the range of 2–5 lm.
3.3 Photoluminescence properties of Ca3(PO4)2:Dy3?
phosphor
The photoluminescence excitation and emission spectra of
Ca3(PO4)2:Dy3? phosphor are shown in figures 3 and 4,
respectively. Multiple peaks are obtained in the excitation
spectra sighted at 483 nm emission wavelength. The exci-
tation peaks were obtained at 326, 351, 366 and 389 nm in
UV region. One of the most prominent peaks which is at
351 nm wavelength is used for the measurement of emis-
sion spectra. Strong emission at 483 and 574 nm in the
blue–yellow region is obtained upon UV excitation attrib-
uted to 4F9/2 ?6H15/2,
6H13/2 transitions of dopant ion
Dy3? [25–27]. The origins of Dy3? emissions at 483 and
574 nm are due to magnetic and electric dipoles. In most of
the compounds studied that, when Dy3? is situated at a low
symmetry (with an omission of inversion centre), the yellow
emission is effective, while the blue emission is tenacious
when Dy3? is situated at a high symmetry (with an inver-
sion centre). From the depicted figure 4, observed blue
emission is more durable than yellow emission.
3.4 Photoluminescence properties of Ca3(PO4)2:Eu3?
phosphor
Figure 5 delineates the photoluminescence excitation
spectra of Ca3(PO4)2 phosphor activated by Eu3? ion
sighted at an emission wavelength of 613 nm. Three char-
acteristic peaks are found at 364, 385 and 397 nm in the
Figure 1. XRD pattern of Ca3(PO4)2 host.
174 Page 2 of 5 Bull. Mater. Sci. (2021) 44:174
near UV wavelength range. The most prominent peak of the
excitation spectrum which is at 397 nm is used to obtain the
photoluminescence emission spectra as shown in figure 6. It
was observed that powerful emission of wavelengths at 594,
613, 617 nm peaked in the orange–red region of the visible
spectrum. These emission wavelengths are assigned to5D0 ?
7F1,7F2 transitions of rare earth Eu3? ion [28–31].
In the second and prominent emission peak, a doublet is
evident; this may be due to the crystal field splitting effect
during the incorporation of dopant ion in the host lattice.
3.5 Chromaticity coordinates of Ca3(PO4)2:Eu3?
and Ca3(PO4)2:Dy3? phosphors
The CIE chromaticity diagram of Ca3(PO4)2:Eu3? and
Ca3(PO4)2:Dy3? phosphors excited by near UV wavelength
Figure 2. SEM images of Ca3(PO4)2 phosphor.
Figure 3. Photoluminescence excitation spectrum of Ca3(PO4)2:
Dy3?, kem = 483 nm.
Figure 4. Photoluminescence emission spectrum of Ca3(PO4)2:
Dy3?, kex = 351 nm.
Figure 5. Photoluminescence excitation spectrum of Ca3(PO4)2:
Eu3?, kem = 613 nm.
Bull. Mater. Sci. (2021) 44:174 Page 3 of 5 174
is shown in figure 7. The colour coordinates of the Ca3(PO4)2:Dy
3? phosphor of the blue colour (483 nm) is
(x = 0.0781, y = 0.1704) and of the yellow colour (574 nm)
is (x = 0.471, y = 0.527). The colour coordinates of the
Ca3(PO4)2:Eu3? phosphor of orange–red colour (613 nm) is
(x = 0.674, y = 0.325). The obtained CIE colour coordi-
nates for Ca3(PO4)2:Eu3? and Ca3(PO4)2:Dy
3? phosphors
are around the edge of the CIE diagram signify the immense
colour purity of their corresponding emissions [32,33]. Both
the Ca3(PO4)2:Eu3? and Ca3(PO4)2:Dy
3? phosphors can be
efficiently excited by near UV wavelength giving strong
visible emissions. Further, the CIE colour coordinates of
synthesized phosphor suggest that these contenders can be
utilized for solid-state lighting [34].
4. Conclusion
The rare earth Ca3(PO4)2:RE (RE = Eu3? and Dy3?) phos-
phors synthesized by wet chemical synthesis. The synthesized
phosphor was characterized for XRD to confirm the phase;
SEM to study morphology, PL excitation and emission. The
colour chromaticity properties were studied using CIE. Colour
coordinates are calculated from the CIE diagram and found
around the edge of the CIE diagram. Ca3(PO4)2:Eu3? phos-
phor gives characteristic orange–red emission, whereas Ca3(PO4)2:Dy
3? gives blue–yellow emissions due to near UV
excitation. The optical properties of the synthesized phosphor
indicate that the reported phosphor can be a potential con-
tender for environmentally friendly based solid-state lighting.
Acknowledgements
A N Yerpude is thankful to Gondwana University,
Gadchiroli, India (project ref. no./GUG/DIIL/609/2020,
dated 14/02/2020), for financial assistance and Gondwana
University, Gadchiroli, for constant encouragement.
References
[1] Holsa J, Laamanen T, Lastusaari M, Malkamaki M, Welter E
and Zajac D A 2010 Spectrochim. Acta Part B 65 301
[2] Krishna R H, Nagabhushana B M, Nagabhushana H,
Chakradhar R P S, Suriyamurthy N, Sivaramakrishna R et al2014 J. Alloys Compd. 589 596
[3] Yerpude A N and Dhoble S J 2012 J. Lumin. 132 2975
[4] Lin C C and Liu R S 2011 J. Phys. Chem. Lett. 2 1268
[5] Pushpendra, Suryawanshi I, Kalia R, Kunchala R K,
Mudavath S L and Naidu B S 2021 J. Rare Earth 26 102144
[6] Ratnam B V, Jayasimhadri M, Jang K , Lee H S, Yi S S and
Jeong J H 2010 J. Am. Ceram. Soc. 93 3857
[7] Ju Z H, Wei R P, Ma J X, Pang C R and Liu W S 2010 J.Alloys Compd. 507 133
[8] Rama Raju G S, Yu J S, Park J Y, Jung H C and Moon B K
2011 J. Am. Ceram. Soc. 95 238
[9] Wu Z C, Shi J X, Gong M L, Wang J and Su Q 2007
Nanosized Mater. Chem. Phys. 103 415
[10] Palan C B, Bajaj N S, Soni A, Kulkarni M S and Omanwar
S K 2015 Int. J. Lumin. Appl. 5 12
[11] Palan C B, Bajaj N S, Soni A, Kulkarni M S and Omanwar
S K 2016 J. Lumin. 176 106
[12] Ramteke S K, Kokode N S, Kohale R L, Yerpude A N and
Dhoble S J 2020 Mater. Today: Proc. 29 876
[13] Hu J, Xie H, Huang Y, Wei D and Seo H J 2014 Appl. Phys.B 114 461
[14] Zhang S, Huang Y and Seob J 2010 J. Electrochem. Soc. 157J261
[15] Naidu B S, Vishwanadh B, Sudarsan V and Vatsa R K 2013
Dalton Trans. 41 3194
[16] Yerpude A N and Dhoble S J 2012 J. Lumin. 132 1781
[17] Yerpude A N, Nikhare G N, Dhoble S J and Kokode N S
2019 Mater. Today: Proc. 15 511
Figure 6. Photoluminescence emission spectrum of Ca3(PO4)2:
Eu3?, kex = 397 nm.
Figure 7. CIE chromatic diagram showing the chromatic
coordinates.
174 Page 4 of 5 Bull. Mater. Sci. (2021) 44:174
[18] Dhoble S J and Kore Bhushan P 2015 Optik 126 1527
[19] Wan C and Menga J 2010 Solid State Commun. 150 1493
[20] Nagpure I M, Saha S and Dhoble S J 2009 J. Lumin. 129 898
[21] Zhang X, Zhou L and Gong M L 2013 Optic. Mater. 35 993
[22] Ji H, Huang Z, Xia Z, Molokeev M S, Chen M, Atuchin V V
et al 2015 J. Am. Ceram. Soc. 98 3280
[23] Li K, Zhang Y, Li X, Shang M, Lian H and Lin J 2015
Dalton Trans. 44 4683
[24] Nagpure I M, Pawade V B and Dhoble S J 2010 Lumines-cence 5 9
[25] Jiao Y, Wu X, Ren Q, Hai Q, Lin F and Wenni B 2019 Opt.Laser Technol. 109 470
[26] Xiang D, Chu Y, Xiao X, Xu J, Zhang Z, Liu Z et al 2018 J.Solid State Chem. 268 130
[27] Panse V R, Yerpude A N and Dhoble S J 2018 J. Mater. Sci.:Mater. Electron. 28 6880
[28] Baig N, Dhoble N S, Yerpude A N, Singh V and Dhoble S J
2016 Optik 127 6574
[29] Liu Q, Li X, Guo J, Wang L, Song J and Zhang Q 2019 DyesPigm. 160 165
[30] Yerpude A N, Dhoble S J and Kokode N S 2019 Optik 179774
[31] Naidu B S, Vishwanadh B, Vasantakumaran S and Vatsa
R K 2011 J. Am. Ceram. Soc. 94 3144
[32] Yerpude A N and Dhoble S J 2013 Micro Nano Lett. 7 268
[33] Yerpude A N and Dhoble S J 2013 J. Lumin. 138 153
[34] Ramteke S K, Kokode N S, Yerpude A N, Nikhare G N and
Dhoble S J 2020 Luminescence 35 618
Bull. Mater. Sci. (2021) 44:174 Page 5 of 5 174