X-ray diffraction experiments, luminescence measurements and first-principles GGAÂ +Â U calculations on YTaO4

The structural and electronic properties of yttrium tantalate (YTaO4) crystal are studied using experimental and first-principles total energy calculations. The band gap of the host lattice from absorption and luminescence experiment is measured to be 5.1 eV. This is close to 5.14 eV reproduced by means of GGA + U approach. In our calculation, we tune both the Hubbard energy U and the exchange parameter J to reproduce the energy gap measured experimentally. It is found that the Hubbard energy U plays a major role in reproducing the experimentally measured energy gap but the exchange parameter J does not. We also calculate the density of states (DOS) using the optimized U to interpret the experimentally measured luminescence spectra. Both the experimental and DOS calculation show that the valence band of tantalate (Ta) system is mainly composed of oxygen (O) 2p states. The lower conduction band is mainly composed of Ta 5d states, while the upper conduction band involves contribution mainly from yttrium (Y) 4d states, with the middle conduction band mainly a mixture of Ta and Y states.