CERIUM CONCENTRATION AND TEMPERATURE-DEPENDENCE OF THE LUMINESCENCE OF SRGA2S4-CE,NA, A BLUE-EMITTING MATERIAL FOR ELECTROLUMINESCENT AND HIGH-CURRENT DENSITY CATHODOLUMINESCENT DISPLAYS

The cerium concentration and temperature dependence of the spectral di stribution, quantum yield, and lifetime of the Ce3+ photoluminescence has been investigated in powders having the composition Sr1-2xCexNaxGa 2S4 (x less than or equal to 0.5). With increasing cerium concentratio n the emission shows a strong shift to longer wavelengths caused mainl y by changes in the ligand field. Despite a relatively small Stokes sh ift (2000 cm(-1)), the emission shows a low concentration quenching up to x = 0.10. Because of the size differences between the Ce3+, Na+, a nd Sr2+ ions, cerium ions possess various environments. Energy migrati on to defects is impeded by the transfer df the excitation energy to t he ions having the lowest emitting states, whose emission exhibits red uced overlap with the absorption of other ions. As a result of the sma ll Stokes shift, at low Ce concentration the luminescence is not affec ted by the thermal quenching up to 500 K. The low concentration quench ing and the high thermal stability are favorable characteristics for u se of this phosphor in electroluminescence and high current density CL screens.