Temperature dependence of Cu⁺ luminescence in barium-phosphate glasses: Effect of rare-earth ions (Sm^3 +, Nd^3 +) and correlation with glass structure

Glasses activated with Cu⁺ ions and rare-earth (RE) metals are attractive as luminescent materials for down shifting in solar cells and various photonic applications. Yet, the thermal stability of the Cu⁺ emission in such, in connection with the effects of RE co-dopants has remained unexplored. Hence, this work reports on the influence of temperature on Cu⁺ luminescence in melt-quenched barium-phosphate glasses, where the effect on such of RE co-dopants Sm^3 + and Nd^3 + is evaluated. Further, the basic structural features of the Cu⁺ and RE-containing glasses is assessed by ³¹P nuclear magnetic resonance (NMR) spectroscopy. The data shows that the PO₄ tetrahedra belonging to terminal units (Q¹) increase upon RE addition, with the most significant structural modification being produced by the large-radius Nd^3 + ions. Moreover, the data shows that the activation energy for the thermal quenching of Cu⁺ emission decreases after RE inclusion, most dramatically for the Cu⁺/Nd^3 + co-doped glass. An observed correlation suggests that the distinct sensitivity of the Cu⁺ luminescence to temperature arises from an indirect effect, namely, the changes in glass structure induced by the RE ions.