Colour centres and luminescence in KCl:Ni crystals

Abstract

AbstractOptical 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 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 centres towards Ni++ ions.