Radiative and non-radiative processes of Ce related transitions in CaGa2S4 and SrGa2S4

The Ce emission appearing in the blue-green region was investigated for CaGa2S4 and SrGa2S4. The room temperature quantum efficiency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa2S4 single crystal grown by the melt method. The quantum efficiency decreased for a 0.8 wt% Ce-doped CaGa2S4 crystal and clear photoacoustic signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds, ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(E-g) level of the Cc ion. Temperature dependent intensity changes observed in this UV emission and in the blue-green emission suggest temperature dependent population transfer from the upper level of E-g to the lower level of T-2g in the excited state of 5d electrons. (C) 2003 Elsevier Ltd. All rights reserved.