Multimodal Photoluminescence in Ca2Nb2O7-based Glass–Ceramics

Lanthanide-doped Ca2Nb2O7 offers versatile and tunable luminescence properties. Previous studies have shown that Pr3+-doped and Pr3+/Er3+ co-doped Ca2Nb2O7 ceramics exhibit non-destructive mechanoluminescence, up- and down-conversion luminescence, and thermoluminescence, with potential for optical temperature sensing. However, to date, niobate glass–ceramics (GCs) remain largely unexplored, although they would offer excellent temperature resistance, high chemical durability, controllable crystallization, and the possibility to combine functional properties. This study investigates Pr3+ single doping and Pr3+/Er3+ co-doping in glass–ceramics prepared from niobium-containing calcium aluminosilicate glasses with the composition 55CaO-(35-x)Al2O3-10SiO2-xNb2O5 (mol%, where x = 0, 10). The aim is to obtain glass–ceramics containing Ca2Nb2O7 crystals with a layered perovskite structure and to evaluate their suitability as hosts for rare-earth ions. The luminescence properties of both parent glasses and GCs were investigated, and it is shown that the glasses show intrinsic luminescence which, when doped, enables sensitization of rare-earth elements via charge transfer. Furthermore, several interesting photoluminescence mechanisms were observed in the doped GCs, including (i) Er3+ up-conversion from the NIR to the visible, (ii) variations in the relative intensities of Er3+ hypersensitive transitions, reflecting changes in site symmetry, and (iii) a charge transfer process to the activator ions under UV excitation. These phenomena extend the accessible excitation range for rare-earth emission. Overall, the developed Ca2Nb2O7 GCs demonstrate efficient dopant integration, confirming their suitability as lanthanide hosts for advanced photonic, sensing and energy conversion applications.