Conoscopic study of strontium-barium niobate single crystals

Optically transparent single crystals of strontium-barium niobate, Sr xBa1-xNb2O6, of different compositions (x 0.26...0.7) were examined with the aid of conoscopic light interference figures. A regular change of the isochrome concentric ring number and diameters consistent with the temperature variation of the value of birefringence is demonstrated by direct observations of polar cuts of optically uniaxial samples. Anomalous violations of the conventional (uniaxial) interference patterns occur occasionaly in some samples being indicative of the existence of biaxial trait in their behaviour even though no voltage is applied. These features may depend on annealing treatments at elevated temperatures. The results of the study show that conoscopic images may serve as a sensitive indicator of the structural state of SBN crystals related to the effects of stress-induced change of optical anisotropy and temperature dependent birefringence parameters

33000 Photons per MeV from Mixed (Lu0.75Y0.25)3Al5O12:Pr Scintillator Crystals

(LuxY1-x)3Al5O12:Pr (x = 0.25, 0.50, 0.75) crystals have been grown by the Czochralski method and their scintillation properties have been examined. Compared to the well-respected LuAG:Pr scintillator, which has so extensively been studied in the recent years, the new mixed LuYAG:Pr crystals display markedly higher light yields, regardless of the value of x. In particular, (Lu0.75Y0.25)3Al5O12:0.2%Pr characterized by a yield of 33000 ph/MeV, an energy resolution of 4.4% (at 662 keV), and a density of 6.2 g/cm3, seems to be an ideal candidate to supercede Lu3Al5O12:0.2%Pr (19000 ph/MeV, 4.6%, 6.7 g/cm3) 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

X-ray photoelectron spectroscopy studies of PrAlO3 crystals before and after thermal treatment

The as-grown PrAlO3 single crystals grown by the Czochralski method are brown colored and after annealing in the reducing atmosphere (20%) H2/N2 they change the color to green. The X-ray photoelectron spectroscopy was used to study the chemical composition and electronic structure of PrAlO3 single crystals before and after the thermal treatment. The core electron lines of praseodymium, aluminum and oxygen were measured and deconvoluted into the synthetic peaks to determine the chemical shifts. The mixed ionic and covalent character of bonds was found. The praseodymium valency may influence the coloration of the PrAlO3 crystal. In the as-grown sample an additional Pr 3d3/2 peak at about 965 eV has higher intensity than that in the annealed one and is attributed to the presence of Pr4+ ions. The measurements showed the reduction of oxygen during thermal treatment and that interstitial oxygen was not removed in this process

Effect of Nitrogen Doping on the Growth of 4H Polytype on the 6H-SiC Seed by PVT Method

score: 0collation: 29-3