The origin of coloration of CaGdAlO 4 crystals and its effect on their physical properties

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Abstract
CaGdAlO4 (CGA) single crystals have been grown in different oxygen concentration atmospheres by the Czochralski method. Crystals grown under an oxygen-containing atmosphere presented an inconsistent brown coloration. The origin of coloration was studied by density functional theory, and the simulated results show the oxygen defects and the absorption matched well with the experimental results. The brown coloration of CGA is due to the interstitial oxygen atoms. The fundamental properties of CGA crystals with different colors, including the crystal density, hardness, thermal and optical properties, were systematically investigated and compared when taking into account the effect of color center inside. The colorless CGA was grown under an inert gas atmosphere and exhibits a wide transparency range of 227–7140 nm. The maximum phonon energy was determined to be as low as 618 cm−1. The colorless CGA host crystal with a disordered structure, good thermal conductivity, low maximum phonon energy and wide transparency is promising for ultrafast ultraviolet and visible laser applications.

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