Luminescence, absorption, and site symmetry of Ce activated SrGa2S4 phosphors

Ce activated SrGa2S4 blue emitting phosphors were examined using electron paramagnetic resonance and x-ray diffraction to determine the local environment and oxidation state of the Ce ion. Photothermal deflection and photoluminescence spectroscopies were applied to determine absorption and emission characteristics. It is found that the majority of the Ce3+ ions substitute for the eightfold coordinated antiprismatic Sr2+ cations in the structure. Our results show that the Ce ions exhibit C3h symmetry; this suggests that they are ninefold coordinated. This coordination may arise from a nearby S interstitial, energetically favorable because of charge compensation. To achieve this symmetry, only minor rearrangements of the eight S atoms in the antiprismatic configuration are required.