ESR and luminescence studies on formation of S2− ions through photochemical reactions in potassium halide crystals doped with sulfur and manganese

Abstract

Remarkable photochemical reactions in potassium halide crystals doubly-doped with sulfur and manganese were investigated by electron spin resonance (ESR) and photoluminescence (PL) measurements. It was found from the PL excitation spectrum that manganese ions were dispersed into lattices as divalent Mn2+ ions and it was further determined by ESR measurements that they were displaced with potassium ions in the form of an Mn2+-vacancy in the quenched sample. After irradiated with deep uv light, it was found by observation of the characteristic vibronic structure of PL emission spectrum, these Mn2+-vacancy ESR centers were disappeared and in tum S2- molecular ions were effectively formed. Then, it was concluded from the analysis of different types of ESR spectra that monovalent Mn+ ions and neutral Mn0 atoms existed at the same time in the lattice. Furthermore, the isolated Mn2+ ions were formed from these Mn+ ions and Mn0 atoms by irradiation of visible light. Such photochemical reactions exhibited the extremely reversible behavior between uv and visible light irradiations. It was confirmed from the angulardependence of corresponding ESR spectra that these three types of manganese centers except for Mn2+-vacancy centers were all isotropic. By the present method, S2- molecular ions were efficiently introduced into potassium halide crystals for the first time.