Spectral and structural characteristics of $\beta$-NaGd$_{1-x}$Eu$_x$F$_4$ at different concentrations of Eu$^{3+}$ ions

Samples of $\beta$-NaGd$_{1-x}$Eu$_x$F$_4$, where 0 $\le x\le1$, were synthesized by the hydrothermal method for the first time. The obtained materials are characterized by methods of X-ray phase analysis, electron microscopy, IR and Raman spectroscopy. For the first time, luminescence spectra and luminescence excitation spectra of $\beta$-NaGd$_{1-x}$Eu$_x$F$_4$ were studied in the entire range of europium concentrations. The absence of complete quenching of the luminescence of the $\beta$-NaGd$_{1-x}$Eu$_x$F$_4$ system was found and it was shown that the excitation of the luminescence of this system by excitation of donor ions (Gd$^{3+}$) leads to a high quantum yield of luminescence.