The effect of impurities on TL emission wavelengths of NaCl crystals

We report emission spectra during thermoluminescence of NaCl crystals doped with Eu, Sr, Ca, Cr and Ni impurities. Crystals were irradiated at ambient temperature with X- or γ-rays prior to measurement. Isometric plots in the wavelength range 200–800 nm reveal only small differences in patterns of TL emission for pure samples and samples doped with Eu, Sr and Ca. However samples doped with Cr and Ni show significant variations characterized by suppressed emission between 390 nm and 520 nm. This is discussed in terms of the efficiency of colouration of the crystals and the state of aggregation of impurity–vacancy dipoles.