Acta Physica Hungarica 71 (3"5), PP. 153-I�91 (1992)

THERMALLY AND DEFORMATION INDUCED FLUORESCENCE IN SODIUM IODIDE

T. R. JOSHI, A. K. NEHATE, MAHMOOD TAHER and L. H. H. PRASAD

ApT)licd PhysicJ Department, Facult~ o… Technology and Engineering M. S. Uni~ermity of Baroda

Baroda 390001, India

(Received 22 April 1991)

The present paper reports the excitation and en¨ spectra of sodium iodide phosphor in three different physical conditions nmne]y (i) as-rece]ved powder forro, (ii) thermally treated NaI powder condition and (iii) NsI tableted condition. The fluores- cence spectr& have been recorded by means of Anª spectrophoto-fluorometer supplied by American Instrument Co. Inc. The examination of fluorescence spectra in different physical conditions of NaI phosphor revewls the fact that fluorescence spectra axe formal significantly influenced by pretreatments. It is presumed that the ch~nge in density of v~cancy, v~cancy pair and dislocation in lattice of NaI on application of pre-treatments is responsib|e for the observed chmage in fluorescence spectra of NaI in different physical conditions.

I n t r o d u c t i o n

The progress made in the ¡ of luminescence of solids has been known for a long time. Nowadays the phenomenon of luminescence is one of the impor- tant branches of solid state physics in the present scientific world. Luminescence materials ate used in a variety of applications like medicine, agriculture, radiation applications, archaeological and geological dating, etc. The luminescence from alks- lihalides has been found very interesting and useful in different fields. Luminescence of alkalihalides, particularly iodides [1-3] has been studied extensively. However, the survey of literature indicates that there is no systematic study of sodium iodide (NaI). Therefore, the present paper reports the fluorescence spectra of pure NaI in different physical conditions.

E x p e r i m e n t a l

This paper discusses the effer of different physical treatments on the fluores- cence spectra of sodium iodide (NaI). The specimens were prepared by the method of recrystallization from squeous solution. They were subjected to thermal and/or mechanical pretreatments. The NaI material was examined for its luminescent be- haviours in the following physical conditions:

Acta Ph~Jica H~ngarica 71, 199~ Akad› Kiad£ Budapcst

144 T . R . 3 0 S H I et a l

240-

210-

180-

T 150-

P,

>. 120- ,,m..,

c

g0- 272

f~ i I !

60- I 248/

30- /

0 200 300

A

370

.~.

200 360 520 wavetength (nm)

Fig. 1. Fluoresce~ce spectra of NaI powder: in u-receJved condition; A - excitation spectra, B - emi~ion spr

(i) As-obtained NaI powder obtained from aqueous solution through recrystal- ]ization.

(ii) As-obtained NaI, annealed and rapidly cooled to room temperature from 500 ~ in open air.

(iii) NaI pe]let obtained from as-obtained material through p]astic deformation. (iv) NaI tablet prepared from 500 ~ air-quenched powder through meehanical

compression. The emission and excitation spectra were recorded for the above mentioned

specimens at room temperature under identical experimental conditions. The in- strument used to study the excitation and emission spectra is Aminco-Bowmann spectrophoto-fluorometer supplied by American Instrument Co. Inc. Sodium iodide

Acta Pkyeiea H~~14rica 71, 199~

THERMALLY AND DEFORMATION INDUCED FLUORESCENCE 145

240 -

210-

180 -

150- e s

o

12o- t ~ r -

.E 9 0 -

I 6 0 - j ! I I !

30- Ÿ I /

/ !

0 200

296

272~ t% I q I t l

A

396 f% �9 �9

I I l i I I

t

I I I 300 200 360 520

waveLength (nm)

Fig. 2. Fluorr162 spectr& of Nazi powder =dter mmealed at 500 "C =red then cooled to r o o m tempr162 in a~r; A - excit~tion spectra , B - e m i u i o a spectr~

in powder forro used in the present work was supplied by 'Loba Chemi Wien-Fi- schamed Austramal-Preparate' Company.

In all cases, the excitation spectrum of a given specimen was flrst observed and subsequently its emission spectrum stimulated by observed excitation was recorded. Each excitation and emission band is specified by the wavelength at which its peak appears.

Acfa PhT#ic" Hvng~vic~ 71, 199J~

1 4 6 T . R . JOSHI et al

3004

270-

240-

210-

I 180-

~ 150-

c

120-

90-

60 -

3 0 -

272

I

I I I I I ! I

232Ÿ ^ ! ~V

/~72

! i ! i ! i I \ ,

i i I i

! 1 ! i t

t F t

0 i i i 200 300 200 400 600

wavetength (nm)

Fig. 3. Fluorescence spectra of NaI pellet, obtained from M-received Na[ powder; A - exci tat ion spectr~, B - emissŸ spectra

Resu l t s and discuss ion

The fluorescence characteristŸ exhibited by sodium iodide in different phys- ical conditions ate as follows:

(i) Untreated NaI phosphor exhibits two excitation bands at 248 and 272 nm. These excitstion bands produce dominant emission �91 370 nm along with a hump st 460 nm (Fig. 1).

Acta Phy*ics H~.gs~ca 71, 199,~

THERMALLY AND DEFORMATION INDUCED FLUORESCENCE 147

4000-

1 3000

> ,

c ~ 2000

1000

296

II I I

I … I Ÿ ,Ÿ

200 520

A

420

. / '~ . ~ " , j ,

300 200 350 wavetength (nm)

Fig. 4. Fluorescence spectra of NaI pellet obtained from the powder annealed at 500 eC, then cooled to room temperature in air, A - excitation spectra, B - enª spectra

(ii) The fluorescence spectra displayed by NaI phosphor are found sensitive to thermal treatment. The main emission, 370 nm, shifts towards the higher wavelength side, i.e. to 396 nm on execution of pre-heat-treatment. The overall intensity of the fluorescence spectrum also increases with thermal treatments. The corresponding excitation wavelengths are 272 and 296 nm (Fig. 2).

(iii) Like pre-heat-treatment, mechanical pre-treatment also enhances the overall intensity of luminescence and shifts the dominant emission band on the higher wavelength side (Figs 3 and 4).

Acta Ph~sir H~nga~'ica 71, 199~

148 T .R. JOSHI et al

(iv) It is very clearly found that the pellet of 500 ~ air quenched NaI material exhibits optimum fluorescence output among the specimens under examina- tion. It is believed that the emission band exhibited by pure NaI powder may be

associated with the crystallinity of the material or ah inherent metallic impurity present in the phosphor. The change in fluorescence behaviours of NaI specimens on application of thermal and/or mechanical treatment may be on account of the change in density of point defect, migration of point defects, and diffusion of ah inherently present impurity in NaI material. It is quite obvious that the concentra- tion of point defect and dislocation density is high in pretreated specimens due to thermal or mechanical shock. This new situation is responsible for the high fluo- rescence output and other changes in fluoresecence spectra of NaI in the thermally and/or mechanically treated specimens.

References

1. R. V. Joehi, J. K. Wmly, Acta Cryst., A-33, 344, 1977. 2. W. R. S. Gm-to~t, The Astrophysics Journal, 165, 23, 1971. 3. H&yuhi T. Salid, Solid State Comm., 17, 945, 1975.

Acta PhTsica H~noarice 71, I99Z