Optical-Absorption in Undoped Yttrium-Aluminum-Garnet

Room‐temperature optical absorption over a large dynamic range is reported for single‐ crystal undoped yttrium aluminum garnet (Y3Al5O12 or YAG). Absorption results are presented for the energy ranges 1.8 to 3.0 and 4.5 to 6.5 eV. For this work, ultraviolet (UV) absorption measurements were performed on four different boules of Czochralski‐grown undoped YAG. Absorption features were observed at 4.8 and 5.6 eV which can be attributed, at least in part, to trace impurity concentrations. Along with the UV measurements, calorimetric absorption results are presented at several laser wavelengths in the visible and near infrared (IR). The calorimetric results suggest a value of 1.5×10−3 cm−1 for the absorption coefficient of undoped YAG in the red and near IR. From the combination of UV and calorimetric measurements, an empirical estimate of the absorption coefficient from the visible to the UV is presented for undoped YAG. In addition to the absorption spectra, detailed chemical analyses and sample histories are given for the as‐grown optical quality YAG utilized herein

Electrical Conductivity in Magnesium-Doped Al_2 O_3 Crystal at Moderate Temperatures

AC and DC electrical measurements between 273 and 800 K were used to characterize the electrical conductivity of Al_2 O_3:Mg single crystals containing [Mg]^{0} center. At low fields contacts are blocking. At high fields, electrical current flows steadily through the sample and the I-V characteristic corresponds to a directly biased barrier whit a series resistance (bulk resistance). AC measurements yield values for the junction capacitance as well as for the sample resistance, and provide perfectly reproducible conductivity values. The conductivity varies linearly whit the [Mg]^{0} concentration and a thermal activation energy of 0.68 eV was obtained, which agrees very well with the activation energy previously reported for motion of free holes.Comment: LaTeX, 6 pages, 3 eps figures included. Contributed Paper to the "International Conference on Defects in Insulating Materials" (ICDIM 2000), Johannesburg, South Africa, 3-7 April, 200

Room-temperature Optical Absorption In Undoped α-al2o 3

Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α-Al2 O 3 single crystal. Absorption data are presented in two energy ranges: 0.94-3.5 eV and 4.5-8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochralski-grown single-crystal Al 2 O3 with differing starting material purities. The initial powder purities were 99.99%, 99.999%, and 99.999999%. In addition to the vuv measurements, calorimetric absorption results obtained in the visible and near-infrared (ir) are presented. An empirical formula is obtained that provides an estimate of the absorption coefficient from the near-ir to the vuv for undoped Al2 O3. Detailed impurity analyses and sample histories are given for the optical-quality α-Al2 O3 utilized herein.67127542754

Room-Temperature Optical-Absorption in Undoped Alpha-AL2O3

Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α‐Al2 O3 single crystal. Absorption data are presented in two energy ranges: 0.94–3.5 eV and 4.5–8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochralski‐grown single‐crystal Al2 O3 with differing starting material purities. The initial powder purities were 99.99%, 99.999%, and 99.999999%. In addition to the vuv measurements, calorimetric absorption results obtained in the visible and near‐infrared (ir) are presented. An empirical formula is obtained that provides an estimate of the absorption coefficient from the near‐ir to the vuv for undoped Al2 O3 . Detailed impurity analyses and sample histories are given for the optical‐quality α‐Al2 O3 utilized herein

Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics

Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044