Spectral and Structural Characteristics of (Lu1 – xEux)2(WO4)3 Tungstates

The structure, luminescence, and IR absorption spectra of (Lu 1 – x Eu x ) 2 (WO 4 ) 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 C 2/ 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 (Lu 1 – x Eu x ) 2 (WO 4 ) 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 Eu 3+ ions is observed in samples with monoclinic structure C 2/ c at x ~ 0.9.