Increasing the intensity of the glow of the phosphor Gd$_2$O$_2$S : Tb(3–7 mol.%), caused by a change in the distribution of the Tb$^{3+}$ activator over the real crystal lattice

Luminophores Gd$_2$O$_2$S : Tb(3–7 mol.%), obtained through the stage of sol-gel formation of Gd$_2$O$_3$ : Tb precursors with their subsequent sulfidation in sulfur vapor with LiF flux at 700oC, showed high luminescence efficiency. The characterization of the obtained samples by a set of physicochemical methods established that an increase in the concentration of the Tb$^{3+}$ activator leads to its specific distribution: over gadolinium vacancies ($V_{\mathrm{Gd}}$)"', by replacing Gd$^{3+}$ ions and concentrating it at the boundaries of crystallites. It is noted that in this case, the morphology of crystallites changes, the short-range order of the structural unit of the lattice (Gd$_2$O$_2$) changes with the introduction of S$^{2-}$ ions into oxygen vacancies [$V_{\mathrm{O}}$]$^{\bullet\bullet}$ or the substitution of S$^{2-}$ anions, as a result of which the long-range order of the anionic sublattice is violated and the band gap decreases. At high concentrations of the photoluminescence activator Tb$^{3+}$ 7 mol.%, radiation quenching does not occur due to the presence of the GdOF and TbOF phases. Variations of these effects with an increase in the Tb$^{3+}$ concentration lead to an increase in the intensity of the emission in the green region of the $^5D_4\to^7F_j$ transitions and a decrease in the intensity of the emission in the blue region of the $^5D_3\to^7F_j$ transitions.