Optical properties of manganese-doped yttrium orthoaluminate crystals (Mn:YAlO 3 ), grown by the Czochralski technique, are reported. Luminescence and absorption spectra indicate the presence of Mn 4ϩ ions in as-grown crystals, and Mn 3ϩ , Mn 4ϩ , and Mn 5ϩ ions simultaneously in photoexcited crystals. A permanent diffraction grating, erasable by heating, was obtained in the crystals with diffraction efficiency of more than 50% at 514.5 nm reading wavelength and 1-2 % in 632-930 nm wavelength range. Reading at wavelengths longer than 630 nm did not damage the recorded grating. The electro-optical effect observed in the photoexcited crystals implies that manganese ions disturb the YAlO 3 crystal structure so that it becomes noncentrosymmetric.

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We report on the synthesis and characterization of ZnO and Er-doped ZnO nanostructures. ZnO powders were synthesized by the coprecipitation and the combustion techniques. ZnO powders prepared by the coprecipitation method exhibit sheet-like nanostructures. The sheet thickness is found to be less than 100 nm. The structural and spectroscopic properties of ZnO powders and sheetlike nanostructures have been investigated and discussed. The x-ray and Raman studies show the effects of Zn deficiency on sintering the ZnO samples at about 1300 • C in air. The luminescent properties of ZnO:Er 3+ nanostructures have been illustrated through emission and Raman spectroscopy.

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Blue and green cw upconversion lasing in Er:YLiF 4

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