UV to NIR Down-Shifting in Yb3+-Doped Phosphate Glass via Divalent Tin Centers

The conversion of ultraviolet (UV) to near-infrared (NIR) photons is demonstrated for the first time in Yb3+-containing glass via Sn2+. Glasses with barium phosphate matrix were prepared by melt-quenching adding 2 mol % Yb2O3 alongside SnO up to 10 mol %. The investigation encompassed X-ray diffraction (XRD), UV–vis-NIR absorption, 119Sn Mössbauer spectroscopy, and photoluminescence (PL) spectroscopy measurements with emission dynamics assessment. XRD data showed that the amorphous nature of the glasses is maintained within the range of dopant concentrations considered, while the optical absorption, 119Sn Mössbauer, and PL data supported the occurrence of divalent tin centers. The NIR PL data showed that exciting Sn2+ centers around 290 nm results in the NIR emission from Yb3+ near 1000 nm which becomes more intense with the increase in SnO. The Yb3+ decay curves revealed a rise time for the 2F5/2 emitting level followed by a single exponential decay. An energy transfer process proceeding via charge transfer states involving tin (donor) and ytterbium (acceptor) was proposed to account for the enhanced UV-excited NIR emission from Yb3+ ions.