Spectral and structural characteristics of molybdates (Lu$_{1-x}$Eu$_{x}$)$_{2}$(MoO$_{4}$)$_{3}$

The structure, the photoluminescence, and IR absorption spectra of solid solutions (Lu$_{1-x}$Eu$_{x}$)$_{2}$(MoO$_{4}$)$_{3}$ have been studied over a wide range of europium concentrations $(0\le x\le1)$. It has been found that there is a correlation between the structure and the spectral characteristics of these compounds. Three types of crystal phases are sequentially changed as the europium concentration increases. The photoluminescence and IR absorption spectra of the monoclinic phase with space group $P2_1/a$ have been studied for the first time. The glow maximum at a resonant excitation of Eu$^{3+}$ ions is shown to be observed in the samples with orthorhombic structure $Pba$ 2 at $x\sim$ 0.8. The samples existing in monoclinic $P2_1/a$ phase at $x\sim$ 0.2 demonstrate the maximum luminescence intensity upon excitation in the band with the charge transfer.