Single crystals of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 were grown by the Czochralski method. Structure analysis of the single crystals by X-ray diffraction (XRD) revealed that (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 crystalize in monoclinic cells (space group P21/c), a = 5.3905(8) Å, b = 8.5605(11) Å, c = 13.957(2) Å, β = 112.223(6)º, and a = 5.3921(7) Å, b = 8.5688(10) Å, c = 13.9172(14) Å, β = 111.980(5)º, respectively. One of the two different rare-earth sites is preferentially occupied by La and Gd atoms or by La, Ce and Gd atoms, and the other is occupied by Gd atoms only. Peaks attributed to the 4f-4f transitions (8S7/2–6G7/2 and 8S7/2–6Ix) of Gd3+ and 4f-5d transitions of Ce3+ were observed in the absorption spectra of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 single crystals.
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