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 Mossbauer 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 Mossbauer 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 Mossbauer 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.