Spectral and Structural Characteristics of (Lu1 – xEux)2(WO4)3 Tungstates
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The structure, luminescence, and IR absorption spectra of (Lu1 – xEux)2(WO4)3 solid solutions are studied in a wide range of europium concentrations (0 ≤ x ≤ 1). As the europium concentration increases, two types of crystalline phases sequentially alternate. An orthorhombic phase (space group Pbcn) of tungstate solid solutions is observed at 0 ≤ x < 0.5. In the range 0.5 ≤ x ≤ 0.8, along with the orthorhombic phase, a monoclinic phase (space group C2/c) appears; at x > 0.8, the solid solution has a monoclinic structure. The correspondence between the structure and spectral characteristics of these compounds is found. A change in the structure state leads to not only changes in luminescence spectra, but also in tungstate luminescence excitation spectra. In connection with the hydrophilicity of (Lu1 – xEux)2(WO4)3 solid solutions, the water adsorption isotherm for tungstate samples and its effect on their spectral and structural characteristics is studied. It is found that the luminescence maximum under resonant excitation of Eu3+ ions is observed in samples with monoclinic structure C2/c at x ~ 0.9.
Keywords:phosphors for light-emitting diodes tungstates of rare-earth elements X-ray diffraction analysis IR spectroscopy luminescence spectra
The authors are grateful to the Shared Service Center of the Institute of Solid State Physics of the Russian Academy of Sciences for IR spectroscopy studies of samples and their morphology. The authors are grateful to N.F. Prokopyuk for assistance in experiments.
This study was performed within the State contract of the Solid State Physics Institute, Russian Academy of Sciences.
CONFLICT OF INTEREST
The authors declare that they have no conflicts of interest.
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