Laser-induced phosphorescence studies of doubly-doped CaS phosphors

Effect of killer impurities (Fe, Co and Ni) on excited state life-times in CaS phosphors, doped with copper and having variable concentrations of iron, cobalt and nickel has been studied in this paper. The phosphors have been synthesized, and, then using a nitrogen laser as the excitation source, their decay-curve analysis has been done. Various strong emissions have been detected and the corresponding excited state life-time values measured. These studies are conducted at room temperature. Very interesting results are obtained with the addition of killer impurities in the phosphors with single impurity. Life-time values found to decrease appreciably with the addition of killer impurities (at lower concentration) in the singly doped phosphors. These studies are important as the excited state life-time of the sulphide phosphors prepared by flux method converge to the longer side only, but with the addition of killer impurities at a particular concentration, values of the life-times decreases up to large extent. At higher concentration of killer impurities deeper traps contribute to the phosphorescence, leading to the much higher increase in life-time values.