Physicochemical Properties of Tin and Neodymium Co-Doped Phosphate Glasses: Tuning the UV-Excited Nd³⁺ NIR Emission via Sn²⁺

This work reports on various physicochemical properties and energy conversion processes in phosphate glasses containing Sn²⁺ and Nd³⁺ ions of interest for luminescence-based applications. The glasses were prepared by melting with 50P₂O₅-(49 - x)BaO-1Nd₂O₃-xSnO (x = 0, 1.0, 3.0, 5.0, 7.0, and 9.0 mol %) nominal compositions and characterized by X-ray diffraction, ¹¹⁹Sn Mössbauer spectroscopy, density and related physical properties, Raman spectroscopy, differential scanning calorimetry, dilatometry, optical absorption, and photoluminescence (PL) spectroscopy. X-ray diffraction confirmed the noncrystalline nature of the glasses. The ¹¹⁹Sn Mössbauer evaluation allowed for estimating the relative amounts of Sn²⁺ and Sn⁴⁺ in the glasses, which showed that Sn²⁺ occurrence was favored. The densities showed variations without definite trends; additional physical parameters were then determined such as Sn²⁺-Nd³⁺ distances based on ¹¹⁹Sn Mössbauer results. The characterization by Raman spectroscopy showed no significant structural variation was induced as SnO replaced BaO. The thermal properties of the codoped glasses assessed were however found to be impacted mostly by Sn²⁺ at high nominal SnO contents. Absorption spectra supported consistent occurrence of Nd³⁺ ions among the codoped glasses. The PL evaluation showed that exciting Sn²⁺ centers in the UV (e.g., near 290 nm) results in near-infrared emission from Nd³⁺, which was maximized for SnO added at 5 mol %. The visible PL data were consistent with the presence of Sn²⁺ in the glasses and showed dips in the emission spectra, indicating the energy transfer to Nd³⁺ ions. The Nd³⁺ decay times were however similar among the different samples.