Investigation of the structural aspects in the formation of optical properties of the GeO$_2$–Eu$_2$O$_3$–Ag nanosystem

The structural characteristics of the 95GeO$_2$–5Eu$_2$O$_3$, 94.9GeO$_2$–5Eu$_2$O$_3$–0.1Ag, and 99.9GeO$_2$–0.1Ag xerogels annealed in air at the temperature $T_{\mathrm{an}}$ = 850$^\circ$C have been studied using X-ray diffraction and small-angle neutron scattering. It has been established that the significant change in the relative intensity of the $^7F_0$ $\to$ $^5L_6$ and $^7F_0$ $\to$ $^5H_6$ luminescence excitation bands of Eu$^{3+}$ ions upon introduction of silver correlates with the decrease in the characteristic sizes of polydisperse clusters formed during annealing. The character of the changes in chemical bonds in the system due to the clustering and their role in the formation of optical properties have been analyzed.