Excitation mechanism of Bi3+ luminescence centres in CaS

A systematic approach to investigate the excitation mechanism of Bi³⁺ luminescence centres in CaS has been made from simultaneous measurements of photoluminescence (PL) and photoconductivity (PC), thermoluminescence (TL) and thermally stimulated conductivity (TSC). Changes in PL and PC have been studied in the temperature range 295–505 K. An attempt has been made to explain the correlation between these phenomena with a simple trapped-carrier-free-carrier recombination model. It is found that the charge transfer process dominates in all these phenomena. Conductivity is primarily due to electron traffic through the conduction band, whereas their subsequent recombination through the excited state (³P₁) accounts for the characteristic emission of Bi³⁺.