Photostimulated Thermoluminescence in Additively Colored KCl

Abstract

Thermoluminescence is observed in additively colored alkali-halide crystals following illumination at low temperature with light of wavelength in the absorption bands of the sample ($F,K$, and $L$ bands) and subsequent heating. In this method one deals with only one type of carrier (electrons) and with one type of activator (negative-ion vacancies). Thus, the nature of the trap and the trapping mechanism can be studied under circumstances which avoid the complications intrinsic to the thermoluminescence of x- or $\gamma$-irradiated samples. At least two types of traps are present besides the $F^{\prime }$ in KCl in the temperature range 55-300°K. Hence the quantum yield of the $F\to F^{\prime }$ optical conversion is less than 2. No traps were found associated with fresh dislocations. Two different mechanisms of trap filling have been observed, one through the conduction band, and another through tunneling from the lower excited state of the $F$ center to a neighboring trap.