Temperature Dependent Spectroscopic Properties of Cu⁺ and Dy³⁺ Co-Doped Phosphate Glass: Band Gap Analysis and Cu Nanocluster-Enhanced Dy³⁺ Luminescence

This paper reports on the effects of temperature on light absorption and emission in Cu⁺ and Dy³⁺ co-doped phosphate glass, which is of interest for photonic applications. First, the temperature dependence of the absorption edge of the glass in connection with Cu⁺ ions absorption was assessed. A thermally- induced red shift attributed to Cu⁺ ion-lattice interactions was observed and analyzed through optical band gap determinations in the context of indirect-allowed transitions. Application of the Varshni model for the dependence of the energy gaps with temperature allowed to estimate the 0 K energy gap at 2.87 (±0.01) eV. Furthermore, Dy³⁺ photoluminescence (PL) along with Cu nanoparticles (NPs) absorption was monitored in real-time during an isothermal treatment by the in situ concurrent PL and absorption microspectroscopy technique. Periods of enhancement and quenching of Dy³⁺ emission linked to bidirectional energy transfer processes involving nonplasmonic Cu clusters and plasmonic Cu NPs were revealed. The formation of Cu NPs was promoted by tin(II) used as reductant. It is the first time to the author’s knowledge that the 0 K energy gap is estimated for a highly Cu⁺-doped glass and that the enhancement of Dy³⁺ PL by Cu clusters is exposed.