Thermal quenching, cathodoluminescence and thermoluminescence study of Eu²⁺ doped CaS powder

In order to determine the suitability of Eu²⁺ doped CaS for phosphor-converted light emitting diodes, photoluminescence, cathodoluminescence mapping, thermal quenching of luminescence and thermoluminescence studies of this phosphor were carried out. Thermal quenching in CaS:Eu²⁺ is ascribed to energy transfer to impurities and to electrons activated to the conduction band states. The decay time of Eu²⁺ was partially influenced by oxygen impurities present in the phosphor. Persistent luminescence was observed, originating from trapping and detrapping of electrons by the sulfur or oxygen ion vacancies. The kinetic parameters of the persistent luminescence, namely activation energy (E) and order of kinetics of γ-irradiated CaS:Eu²⁺ were determined using initial rise and repeated dose methods, respectively.