Synthesis and optical properties of cerium doped Li7La3Hf2O12 with tetragonal garnet structure

Abstract

The new polycrystalline samples of Li7La3Hf2O12:xCe (x = 0.00–3.30%) with tetragonal garnet structure have been prepared using a conventional solid state reaction. The phase composition, morphology and optical properties of undoped and cerium doped compounds have been characterized by powder X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance, diffuse reflectance and photoluminescence spectroscopy. The absorption bands at 2.5eV (496nm) and 3.3eV (375nm) are associated with processes of light absorption in F-centers in tetragonal Li7La3Hf2O12. The origin of luminescence in Li7La3Hf2O12 can be explained by the creation and relaxation of self-trapped exciton localized in [HfO6]8- system. The Ce ions in Li7La3Hf2O12:xCe (x = 0.00–3.30%) have predominantly the Ce4+ valence state, and no luminescence of Ce3+ is observed. The increase in the cerium concentration in Li7La3Hf2O12 leads to a reduction of the photoluminescence intensity associated with intrinsic luminescence centers. Using the temperature dependence of luminescence, the activation energy of temperature quenching of intrinsic luminance was calculated.