Effect of temperature on lyoluminescence of divalent impurity doped sodiumchloride

The effect of temperature on the lyoluminescence (LL) of divalent impurity doped sodium chloride has been reported. When the NaCl crystallites irradia ted using Co-60 source are dissolved in distilled water, initially the LL i ntensity increases with time, attains a maximum value, then it decreases an d finally disappears. The peak I-m of LL intensity versus time curve initia lly increases with temperature, attains an optimum value at a particular te mperature and then it decreases with further increase in temperature. Howev er, the total intensity I-T and time t(m) corresponding to the peak of LL i ntensity versus time curves decrease with increasing temperature of the sol ution. The peak intensity I-m is maximum at a particular temperature becaus e of the competition between increase in rate of dissolution of NaCl with t emperature and decrease in efficiency eta and density of F-centres with tem perature. The value of time t(m) decreases with increasing temperature of t he solution because of the increasing rate constant for the recombination o f hydrated electrons with holes. The efficiency eta and n(F) decrease with temperature and therefore, the total intensity I-T decreases with increasin g temperature of the solution. The decay time tau depends inversely on the rate of dissolution alpha, of solute in the solvent. Since alpha increases with increasing temperature of the solution, tau decreases with increasing temperature of the solution.