Mechanism of X‐Ray Emission in KBr:Cu Single Crystals

Abstract

AbstractA study is made of the mechanism for Cu‐luminescence in KBr:Cu single crystals excited by ionizing radiation. The following results are obtained: In the spectral range 200 to 1200 nm the same emission band (centred about 392 nm at 77 °K) occurs as is obtained by means of u.v. excitation at 265, 235, and 210 nm. Under optical stimulation in the F band the same emission band at 392 nm is again observed. The build‐up of the 392 nm band under X‐ray and F light stimulation in the temperature‐range 77 to 700 °K is also studied, and the results are found to be complex. KBr:Cu samples which are X‐irradiated at 77 °K, or F‐stimulated at 77 °K after X‐ray irradiation at 290 °K, show four glow peaks of thermoluminescence due to Cuimpurities in addition to the glow peaks of pure KBr crystals. Emission spectra under all glow peaks are also observed; in these spectra the emission band due to Cu is alway present. Measurements of the thermal bleaching of crystals which have been X‐irradiated at 77 °K are correlated with the intensity‐changes of the photoluminescence band of the Cu emitter. The assumption that emission under X‐irradiation can be explained as an alternate trapping of free holes and electrons by the emitter centre Cu+, is consistent with most of the results.Thermoluminescence and thermal bleaching experiments are also discussed. It is suggested that some of the glow peaks due to Cu impurities may be explained in terms of electron traps bound to Cu+ ions substituted in the lattice.The presence of these traps seems to explain the observed build‐up of the 392 nm emission band under X‐irradiation, and the observed effects after an ageing at different temperatures.