Preparation and optical properties of transparent glass-ceramics containing LiGa5O8∶ Cr3+
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Transparent glass-ceramics containing LiGa5O8∶Cr3+ crystallites have been prepared by heat treatment of Li2O-Ga2O3-SiO2-Cr2O3 glassy material. Average crystallite size evaluated from the full-width at half-maximum of the X-ray diffraction lines varies from about 3–7 nm as the heat-treatment temperature increases from 650 °C to 800 °C. The ligand field strength of the Cr3+ ion estimated from optical absorption measurements increases with an increase in the heat-treatment temperature. The fluorescence spectra of the glass-ceramics resemble that of LiGa5O8∶ Cr3+ polycrystal. In particular, for the specimen containing a crystallite of 7 nm, intense emission due to the 2E→4A2 transition has been observed. These optical measurements demonstrate that the Cr3+ ions are incorporated into LiGa5O8 microcrystals in the present glass-ceramics. For the transparent glass-ceramics and LiGa5O8∶Cr3+ polycrystal, the temperature dependence of the peak position of the zero-phonon line (R-line) has been analysed assuming that the electronic transition is described by the Raman process and the vibrational density of state is expressed by the Debye model. The Debye temperature of the transparent glass-ceramics is slightly lower than that of LiGa5O8∶ Cr3+ polycrystal, indicating that the softening of the phonon occurs in the LiGa5O8∶Cr3+ microcrystal precipitated in the transparent glass-ceramics.
KeywordsCrystallite Size Fluorescence Spectrum Optical Absorption Electronic Transition Optical Measurement
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