Photo-Electro-Luminescence of ZnS: (Cu, Ce) and ZnS: (Ag, Ce) Phosphors

Abstract

The enhancement and quenching of the prominent emission bands at 4700 A and 5300 Ä of ZnS: (Cu, Ce) and 4600 A and 5200 A of ZnS: (Ag, Ce) on single or simultaneous application of a sinusoidal electric field and 3650 A UV radiation have been studied. The cell was a parallel plate type condensor consisting of a glass plate with a transparent conducting surface, a suspension of the phosphor in castor oil, a mica sheet (about 100 |im thick) and an aluminium plate. Sinusoidal voltage for field excitation was obtained from an audio frequency oscillator coupled to a wide band amplifier. The PL excitation was done by 3650 Ä radiation from a high pressure murcury lamp operated at constant voltage. A constant deviation spectrograph was used as a Reprint requests to Dr. L. N. Tripathi, Department of Physics, University of Gorakhpur, Gorakhpur 273001/ Indien. monochromator for studying the spectral distribution of the luminescence emission. PEL was obtained by combining the excitation of EL and PL. The PEL intensity was measured at 4700 and 5300 A in ZnS: (Cu, Ce) and at 4600 and 5200 A in ZnS: (Ag, Ce). At these wavelengths the phosphors give maximum EL and PL emissions.For detecting the integrated light output of EL, PL and PEL emission, an RCA IP21 photomultiplier tube was used. The output terminals of the photomultiplier were connected to a sensitive galvanometer whose deflections give the integrated light intensity in arbitrary units.Figures 1 and 2 represent the variation of PL, EL and PEL emission intensities with excitation time. It is apparent that PEL first increases sublinearly with time of excitation. From a comparison of the PL, EL and PEL emission intensities it is found that in PEL both bands (4600 Ä and 5200 Ä) are enhanced in ZnS: (Ag, Ce) (Fig. 1), that the 5300 Ä band in ZnS:(Cu, Ce) is quenched at all concentrations (Fig. 2)