A method for preparation of ZnS: (Cu, La) and ZnS: (Ag, La) phosphors is described. Photo and electroluminescence of these phosphors have been studied. The voltage and frequency variation of EL brightness have also been reported. The results agree with the collision-excitation mechanism in the Schottky barrier. The emission of blue, green and yellow bands has been interpreted in terms of different electronic transitions. Simultaneous action of both the field and the 3650 Å radiation has been studied. An attempt has also been made to explain the quenching and enhancement.

ZnS:Gd, ZnS: Cu, Gd and ZnS: Mn, Gd phosphors have been prepared by firing the samples in argon atmosphere. Spectral distributions in these phosphors are discussed with appropriate mechanism. ZnS:Cu, Gd and ZnS:Mn, Gd are found to be examples of multiple band phosphors. Enhancement and quenching of the emission band intensities of all these phosphors have been studied inpel emission. It is observed that Gd³⁺ ions play an important role in transferring their excitation energy to other centres. The voltage and frequency variation ofel brightness are in agreement with collision excitation mechanism in Schottky barrier at the metal semiconductor interface. Studies in phosphorescence and thermoluminescence of these phosphors have also been carried out. It is observed that trap-depth changes slowly with temperature and dopant concentration. The values of trapping parameters have been evaluated. The irregular variation of the life-time of electrons in the traps. with temperature shows the existence of retrapping in these phosphors.

The photo (PL) and electro (EL) luminescence in ZnS: MnLa and ZnS: La have been studied. The enhancement and quenching of emission bands have been observed on the simultaneous application of sinusoidal field and photons. The wave shape, voltage, frequency and temperature dependence of EL brightness have been reported. A study of the phosphorescence and thermoluminescence of these phosphors is also carried out and it is observed that the trap-depth changes slowly with temperature and activator concentration. An attempt has been made to calculate the trap depth by studying temperature dependence of EL brightness. The results are reported and discussed.