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

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 2.5 eV (496 nm) and 3.3 eV (375 nm) 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.