Fast photoluminescence decay processes of doped ZnS phosphors at low temperature

Singly and doubly doped ZnS phosphors have been synthesized in the laboratory. The crystal structure has been determined by X-ray diffraction (XRD) studies. Laser-induced photoluminescence has been observed in ZnS-doped phosphors when these were excited by the pulsed UV N2 laser radiation at liquid nitrogen temperature (77 K). The temperature dependence of lifetimes, trap-depths and decay constant values were investigated for quencher impurities doped ZnS:Mn phosphors. The lifetimes of the orange emission from 4T1-6A1 transition of Mn2+ ions has been found to decrease at liquid nitrogen temperature. Due to downconversion phenomenon fast phosphorescence /fluorescence emission in the visible region is recorded in milliseconds time domain for ZnS:Mn while in case of ZnS:Mn, X (X=Fe, Co and Ni) phosphors lifetime reduces to nanoseconds time domain. A thermally activated carrier-transfer model has been proposed to explain the observed abnormal temperature behaviour of the lifetimes in ZnS:Mn, X (X=Fe, Co and Ni) phosphors. The high efficiency and fast recombination times observed in doped ZnS phosphors make these materials very attractive for optoelectronic applications