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We have performed a density functional calculation for the centrosymmetric neodymium gallate using a full-potential linear augmented plane wave method with the LDA and LDA+U exchange correlation. In particular, we explored the influence of U on the band dispersion and optical transitions. Our calculations show that U = 0.55 Ry gives the best agreement with our ellipsometry data taken in the VUV spectral range with a synchrotron source. Our LDA+U (U = 0.55) calculation shows that the valence band maximum (VBM) is located at T and the conduction band minimum (CBM) is located at the center of the Brillouin zone, resulting in a wide indirect energy band gap of about 3.8 eV in excellent agreement with our experiment. The partial density of states show that the upper valence band originates predominantly from Nd-f and O-p states, with a small admixture of Nd-s/p and Ga-p B-p states, while the lower conduction band prevailingly originates from the Nd-f and Nd-d terms with a small contribution of O-p-Ga-s/p states. The Nd-f states in the upper valence band and lower conduction band have a significant influence on the energy band gap dispersion which is illustrated by our calculations. The calculated frequency dependent optical properties show a small positive uniaxial anisotropy.

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, seems to be an ideal candidate to supercede Lu 3 Al 5 O 12 :0.2%Pr (19000 ph/MeV, 4.6%, 6.7 g/cm 3 ) in various applications. The observed enhancement of light output following the partial substitution of lutetium by yttrium is most probably related to some specific differences in distributions of shallow traps in particular materials.

Experimental results on the growth and characterization of single crystals of mixed perovskite (La,Sr)(Al,Ta)O3 (LSAT), a promising material to prepare substrates for GaN epitaxial layers, growth by the Czochralski method, are reported. The single crystals obtained along <111> orientation up to 20 mm in diameter and 50 mm in length were free of inclusions and macroscopic defects. The optical transmission was measured in the region 200 nm – 3000 nm. For the of <111> oriented LSAT single crystals, its measured unit cell parameter (a = 7.730 Å) matches well to the GaN lattice. The chemical composition was checked by electron microprobe analysis. It was found that it is close to the stoichiometric one. With Lang transmission topography growth striations and dislocations were examined. Data on Vickers microhardness, thermal expansion coefficient, etch pit density and temperature dependence of electrical conductivity and capacitance are reported.

X-ray photoelectron spectroscopy was used to study the chemical composition and electronic structure of the Y 3 Al 5 O 12 :Yb (YAG:Yb) crystals. The contamination of the crystal with carbon and oxygen in the broken under UHV sample was found. The dopant concentration of Yb, in the mixed valence state, was determined as 12 %. The aluminium concentration is lower than a nominal value. The chemical shift analysis shows more ionic bond of Y-O than Al-O.