The present study revealed that the photoluminescence (PL) of copper-doped calcium metaphosphate glasses is influenced by the formation of low-coordinated \({\text{O}}^{2 - }\) anions ( \({\text{O}}_{LC}^{2 - }\) ). Herein, 50CaO·50P₂O₅ (CaP) and 1CuO·49CaO·50P₂O₅ (CuCaP) glasses were prepared by the melt-quenching technique at different melting times (0–40 min). XRD analysis confirmed their amorphous nature, whereas SEM, ATR-IR, and UV–Vis/PL analyses showed simultaneous changes in their structural and optical properties. At 0 and 20 min, SEM micrographs showed aggregate formations likely enriched in CaO, which almost disappeared at 40 min. This was accompanied by strong blue emission at 0–20 min due to the formation of \({\text{O}}_{LC}^{2 - }\) and \({\text{Cu}}^{1 + }\) ions, which almost disappeared at 40 min. This coincided with a slight decrease in the ATR-IR intensity of the \({\text{P}} = {\text{O}}\) peak, thus a slight decrease in \({\upnu }_{{{\text{sy}}}} \left( {{\text{P}} - {\text{O}} - {\text{P}}} \right)\) / \({\upnu }_{{{\text{as}}}} \left( {{\text{P}} = {\text{O}}} \right)\) and an increase in \({\upnu }_{{{\text{as}}}} \left( {{\text{PO}}_{3}^{2 - } } \right)\) relative concentrations. These changes indicate that a prolonged melting time of 40 min leads to aggregate dissolution through the interaction of CaO with BOs in the P-O-P and P = O units. This increases the NBOs formation, resulting in redshifts in the UV–Vis absorption edges and oxidation of \({\text{Cu}}^{1 + }\) to green \({\text{Cu}}^{2 + }\) ions. Overall, the simultaneous changes in the emission intensities of CuCaP and CaP indicate that the formed \({\text{O}}_{LC}^{2 - }\) ion donates its negative charge to \({\text{Cu}}^{2 + }\) , reducing it to a photoluminescent \({\text{Cu}}^{1 + }\) ion. The developed metaphosphate glasses are potentially nontoxic phosphors for biomedical and optoelectronic applications.
