Colour centres and luminescence in KCl:Ni crystals

Optical absorption, thermoluminescence (TL), and monochromatic thermoluminescence (MTL) glow curves, TL and X‐ray luminescence spectra of KCl:Ni crystal are measured. Strong absorption bands appear at 218 and 275 nm due to the transition of an electron from adjacent Cl − ion to Ni ++ ion. The reduction of these bands upon X‐irradiation shows the trapping of electrons by the divalent impurity ions. Only the first peak at 90 °C appears in the TL and MTL glow curve. F bleaching neither produces Z centres nor reduces the V band appreciably but decreases the TL glow curve heavily. These results are also interpreted in terms of electron trapping by impurity ions. Emissions due to decay of STE (Cl   2 −ion trapping an electron in the excited state) near free cation vacancy (445 nm) or unperturbed lattice sites (545 nm) are very weak while those near Ni ++ ions, free (585 nm) or associated with cation vacancies (380 nm), are very strong. This is due to the high mobility of STE and Cl   2 −centres towards Ni ++ ions.