Excitation processes of trivalent cerium ions in calcium thiogallate crystals by hot photocarriers

Excitation spectra for the 5d → 4f emission of Ce3+ ions in CaGa2S4 crystals have been measured at 300 K by using vacuum ultraviolet (VUV) photons, together with reflectivity and absorption-edge spectra. X-ray photoelectron spectroscopy (XPS) experiment has also been performed in order to clarify the contribution of shallow core states to the excitation and reflectivity spectra. Furthermore, cluster calculation by a relativistic discrete variational Xα (DV-Xα) method has been carried out to elucidate the optical transitions resulting in the creation of multiple e-h pairs in CaGa2S4. The excitation processes of Ce3+ ions in CaGa2S4 by hot photocarriers are discussed on the basis of the electronic structure determined from the experiments and calculation.