Thermoluminescence and magnetic susceptibility correlation studies of Dy3+ doped CaSO4 phosphors

Journal of Luminescence 40&41 (1988) 179 180 North-Holland, Amsterdam

179

THERMOLUMINESCENCE AND MAGNETIC SUSCEPTIBILITY CORRELATION STUDIES OF 3~DOPED CaSO Dy 4 PHOSPHORS M.R.MULLA

and S. H. PAWAR

Department of Physics, Science College, Karad, KARAD

-

415 110, M.S., India. 3’) in CaSO

The quantitative estimation of paramagnetic activator ions (Dy

4 is made on the basis of

magnetic susceptibility measurements. These findings are correlated with thermoluminescence studies of these phosphors. I. INTRODUCTION The proved applicability

of

alkaline

earth

___________________________________ Table I - Compositions and values of Ks and N

sulphate phosphors doped with rare earths in radia—

for CaSO4 : Dy phosphors

tion dosimetry has revived the interest of many workers to investigate the luminescence phenomenon underlying the process and to improvise 3.

Composition

the luminescence efficiency of these phosphors~ The authors of this paper have earlier investigated

4 CaSO4:0.075 Dy wt.%

the enhancement effects of thermoluminescence

CaSO4:0.5

(TL), photoluminescence (PL), andtrace electrolumines— 3~ with of charge cence (EL) of CaSO4:Dy compensator Na~ ‘~. In the present investigation

CaSO4:0.075 wt.% (with charge Dy compensator

an attempt has been made to estimate the no.of

CaSO

CaSO

Dy wt.%

4:0.5 Dy wt.% 4 on the

basis of magnetic susceptibility measurements and correlate these findings with the results of thermoluminescence studies.

-

0.30 0.15

i134

+

0.30

4377

-

0.02

4404

+

1.12

9891

-

-

+

3~) in the host CaSO activator ions (Dy

Ks x 10f6 N x l0~6 at Room Temperature

(with charge compensator Na+)

2. EXPERIMENTAL The phosphor preparation has been dealt at

It is worth noting that the undoped2~phosphor and S0 2is diamagnetic, as its constituents Ca 4 are diamagnetic. In case of phosphors without charge compensator it could be noted from the

length elsewhere5. The magnetic susceptibility (Ks) measurements of CaSO~phosphors of ambient

table that the addition of Dy3~makes the phosphor less diamagnetic and paramagnetic for higher con-

activator concentration (Dy3~), with and without trace of charge compensatory (Na~) were done

centration of Dy3~.This is understood as follows: Under equilibrium condition of charge balanc3+ ing, two Dy ions may be incorporated at the substitutional positions (as ionic radii for Ca2~ and Dy3~ ions are nearly the same, 0.99 A ) by

in the temperature range 300-600°K after X-irradiation. 3. RESULTS AND DISCUSSION The values of Ks at room temperature

have

been listed in Table-I for the phosphors studied.

removing three Ca2~ions. Incorporation of paramagnetic

activator

ions

(Dy3~) in

diamagnetic

CaSO 4 gives rise to change in magnetic suscepti-

0022 2313/88/$03.50 © Elsevier Science Publishers BY. (North-Holland Physics Publishing Division)

180

MR. Mu/la, S.H Pawar

billty

of

CaSO4

compensator

ion

phosphors.

Addition

of

/

3 * doped CaSO

Studies of Dy

charge

Na~ from Na2SO4 allows more

dysprosium ions to incorporate in the host increas-

with

activator

ions

(N) in diamagnetic

host

is

with

-

magnetism. number ions per unit Accordingly volume is given by of paramagnetic N

=

where

3 K g2 K is

(

Ks.T J(J+l)

)

concentration

and

this

number

charge compensator. The TL studies of these phosphors completely

support

made

on the basis of Langivin’s quantum theory of para

activator

becomes much more pronounced for the phosphors

ing the degree of paramagnetism of these phosphors. The quantitative estimation of paramagnetic

4 phosphors

output

the

above

findings.

The

integrated

TL

(I

TL~ is found to increase with activator the concentration (fig. 1). However, at higher 3F) concentration

of Dy 3+ (above 0.1 wt.% of D y ‘TL is found jto deteriorate despite of high value

of ‘N’ estimated in the magnetic studies. This concentration quenching is explained on the basis

U~

Boltzmann’s constant

(Ks.T) corres-

of resonant transfer of energy from one activator

ponds to the slope of Ks Vs.l/T plots (not shown

ion to another,

here) which obey Curie’s law, g denotes the spec-

getting dissipated without luminescence at quench-

troscopic splitting

factor,

quantum number and U The factor g~ (J+l)

J

is the total

angular

stands for Bohr magneton corresponds to the effe-

I~2~

ctive number of Bohr magnetons (Peff.) has

the

value 10.66 for Dy. Table

1

for phosphors

with and without charge compensator. N increases

probability of

ing site. The magnetic studies reveal

high values

of ‘N’ for the phosphors with charge compensator. The TL studies support this, as the TL output of charge enhanced

lists the values of N

which has greater

compensator with

single

added

phosphor

non-overlapping

is peak

well as

against the multiple peaks of low TL intensities for the phosphor without charge compensator. The enhancement

effect

is explained

on the basis of

charge compensation.4

100

-

90

—

REFERENCES

80

-

1.

K.S.V.Nambi and T.Higashimura, J. NucI. Sd. Technol (Japan), 7, no.11 (1970), 595.

70

-

2.

A.R. Lakshmanan and K. Ayyangar, Proc.Nat.

~ 60

-

3.

M.R.Mulla and S.H. Pawar, Indian and Appl. Phys. 19 (1981), 24-28.

4.

M.R. Mulla and S.H. Pawar, cence 31 & 32 (1984), 239-24i.

5.

M.R. Mulla and S.H. Pawar, Material Research

Experimerd~ —

~

o

-J ‘-

50

-

Calculated

40 Z

30

-

Bulletin 12 (1977) 929.

-

10

Symp. on Thermoluminescence and Its Application, RRC Kalpakkam, Madras, India (1975), 446.

-

I

0 0.1

0.2

0.3

Concentration of Dy (wf

0.4

0.5

‘I.)

FIGURE 1 Concentration quenching observed CaSO 4 phosphor

in

Dy

doped

J.

J.

of Pure

of Lumines-