Luminescence and energy transfer in thin films of SrGa2S4:Ce

Excitation and photoluminescence (PL) spectra of both nominally undoped and Ce3+-activated SrGa2S4 thin films have been measured at various temperatures between 10 and 300 K. The undoped film shows a complex emission band which appears to involve emission from different defect states. Each defect center effects the recombination kinetics and luminescence spectra in a different temperature region. At 77 K, recombination is dominated by the highly associated defect centers producing an intense red emission band. At higher temperatures, thermalization effects reduce the net capture rates at the competitive defect centers, and recombination through the defect centers at room temperature produces a broad emission band with the peak in the blue spectral region. Evidence of the interaction and energy exchange between defect centers and Ce3+ activator states is inferred from the rise and decay rime measurements of PL emission in SrGa2S4:Ce thin films. As a result of thermalization, the efficiency of energy transfer to Ce3+ ions increases at room temperature but at the expense of introducing a long afterglow into the activator decay. Measurements of temperature dependence of PL intensity suggest that the kinetic model for energy transfer in SrGa2S4:Ce combines aspects of long-range resonance transfer and indirect thermalization from defect stares with subsequent retrapping at the activator sites. In addition, possible mechanisms are discussed which may explain the observed concentration dependence of the Ce3+ fluorescence decay rime. Preliminary results are reported for a thin-film electroluminescent device with a SrGa2S4:Ce, Li phosphor layer prepared by the low-temperature deposition from binary vapors process. (C) 1999 The Electrochemical Society. S0013-4651(97)06-090-4. All rights reserved.