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

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(Eg) level of the Ce 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 Eg to the lower level of T2g in the excited state of 5d electrons.