Rare-Earth-Doped Phosphate Glasses as Upconversion Platforms: The Role of Network Modifiers on Photoluminescent Performance

Upconversion luminescent materials convert near-infrared radiation into higher-energy visible emission, enabling applications in optical thermometry, bioimaging, solar energy conversion, and anti-counterfeiting technologies. In this work, phosphate-based oxide glasses doped with Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ are proposed as tunable host matrices for UC emission. The study focuses on the systematic variation of network modifiers, namely ZnO, Al₂O₃, and Ga₂O₃, in NaPO₃-based glass compositions. These modifiers are expected to influence the local environment of lanthanide ions, affecting energy transfer from Yb³⁺ sensitizers to Er³⁺ or Tm³⁺ activators, and consequently determining emission color and efficiency. Preliminary observations indicate that ZnO-containing glasses enable blue emission through a three-photon upconversion process, although they do not fully suppress the hygroscopic nature of phosphate glasses. Overall, this investigation seeks to establish compositional guidelines for designing phosphate glass hosts with optimized upconversion performance for advanced photonic applications, while simultaneously balancing optical response and structural stability.