^{1}

^{*}

^{2}

Free rotating impurity-vacancy (IV) dipoles in an alkali halide matrix are polarized to the extent of 1/3 of the total number of IV dipoles. An experimental procedure is suggested in this article which will help in the polarization of IV dipoles to the extent of 2/3 of the total number of IV dipoles. In the suggested experimental procedure, the electric field will be applied at first in one direction and then will be applied in succession in opposite direction. Ionic thermocurrent technique is employed to ascertain the increase in polarization of IV dipoles.

Whenever a divalent impurity ion is introduced in an alkali halide matrix, a vacancy is created in its neighborhood for the sake of charge compensation. Vacancy created at the next nearest neighbour position with respect to the impurity ion forms an impurity-vacancy (IV) dipole. It would be justified to mention that at any instant of time, the vacancy will be located at one of the twelve equivalent sites around the impurity ion along <110> di-

rection. The dipole moment (p) of the created IV dipole will be

the interatomic distance. In the absence of electric field, IV dipoles are randomly oriented in the system. In the presence of polarizing electric field

where

where

free rotating dipoles,

After the application of electric field

sented by Equation (3). Saturation polarization

at the polarization temperature

the range C to M of

temperatures, more time is needed because of large relaxation time at these temperatures in accordance with the Arrhenius relation [

where

After getting the frozen-in polarized IV dipoles at the point D of

Consequently, the temperature T increases from _{F} corresponding to point R of

rimentally as a function of T. Plot of I versus T is known as an ITC spectrum [_{F} and

where Q_{o} is the total charge released during an ITC run and _{F} to T. The value of Q_{o} is determined from the area of the ITC spectrum using the relation [

where

obvious from _{m} of ITC spectrum appears at the temperature _{m}, _{F}. Below _{F} will, hence, be represented by

where

polarization because lowering down of the temperature from

tion will be zero and will remain equal to

by Christodoulides [

rature,

Corresponding to recorded ITC spectrum expressed through Equation (6), depolarization current density (J) is represented by

where S is the area of the crystal specimen. Obviously J is depolarization current per unit area. The quantity (Q_{o}/S) in Equation (9) represents the frozen-in polarization

Combination of Equations (8) and (10) gives

Obviously, Q_{o} depends on the area of the crystal specimen under investigation.

To get the number of polarized IV dipoles increased, an experimental procedure is proposed in this article. Frozen-in polarized IV dipoles are obtained following the experimental steps up to point D of _{P} will be applied in the opposite direction with reversed polarity. At the point F of ^{rd} of the total number of IV dipoles. Obviously, one will thus get more number of frozen-in polarized IV dipoles through the suggested experimental procedure. Expression for net frozen-in polarization due to IV dipoles of catagories (a) and (c) will hence be given by

The specimen will now be kept at the temperature ^{st} ITC spectrum of ^{nd} ITC spectrum is recorded after following the experimental steps up to point K of

ITC spectrum recorded corresponding to the polarization conditions up to point D of

may be different than that recorded during ITC spectra. Higher value of

ing in less value of I_{m} and vice-vresa. Higher value of _{m}. If the value of ^{st} run than that of 2^{nd} run due to different rates of rapid cooling in the two cases, one would observe the peak value of ITC spectrum in 2^{nd} run > 2I_{m.}^{ }It is obvious from Equations (2) and (3) that the polarization P is inversely proportional to T. If

_{o} through Equation (10). Higher value of Q_{o} leads to more value of I_{m} according to [

It has to be taken care of in Equation (13) that ^{nd} run after following different experimental steps up to point K of _{m}. It would be justified to mention that it is experimentally very difficult to maintain the same rate of rapid cooling in the two cases being a very fast changing process. However, constant linear heating rate can be maintained easily while recording the ITC runs resulting in the location of ITC peak at the same temperature_{2} crystals doped with Tb^{3+}. While recording the TSPC spectra on this system they have kept (i)

Increment in the number of polarized IV dipoles is also obtained during photo-induced polarization (PIP) when the specimen is simultaneously polarized and irradiated in its suitable absorption band [^{rd} of the total number of IV dipoles can be polarized through the suggested experimental procedure proposed in this article.

The authors are thankful to Dr. R.A Agrawal, the chairman of the institute, for providing necessary facilities. They are also thankful to Mr. A. K. Srivastava, Mrs. Vandana Gupta and Mr. A.K. Arya for their help in computer graphics.

JaiPrakash,11,DevendraPrasad, (2016) A Method for Polarizing More Number of Impurity-Vacancy Dipoles. Journal of Applied Mathematics and Physics,04,461-468. doi: 10.4236/jamp.2016.42051