Monovalent copper-mediated UV to NIR luminescence down-shifting in Yb3+-doped glass

Abstract

The down-shifting of ultraviolet (UV) photons to the near-infrared (NIR) relevant to solar spectral converters and IR lasers is demonstrated for the first time in Yb³⁺-containing glass via monovalent copper. Glass with a barium phosphate matrix was prepared by melt-quenching, adding 2 mol% Yb₂O₃ alongside CuO and SnO at 10 mol% to stabilize Cu⁺ ions. The effect of heat treatment (HT) promoting the precipitation of Cu nanoparticles (NPs) was also investigated. This study entailed measurements by differential scanning calorimetry (DSC), UV-Vis-NIR absorption, X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy with an emission dynamics assessment. The DSC data indicate an influence from Yb³⁺ increasing the glass transition and crystallization temperatures in the copper co-doped glass. The optical absorption and PL data supported the presence of Cu⁺ ions, and in the heat-treated glass the presence of Cu NPs was evidenced by the surface plasmon resonance and XRD data. The NIR PL data showed that exciting Cu⁺ ions in the near-UV preferentially around 375 nm results in the sensitized NIR emission from Yb³⁺ near 1000 nm. However, it becomes diminished in the heat-treated glass. The Yb³⁺ decay curves revealed a rise time for the ²F_5/2 emitting level followed by a single exponential decay. An energy transfer process proceeding via a Cu²⁺–Yb²⁺ charge transfer state is proposed to account for the UV-excited NIR emission from Yb³⁺ ions. Possible interactions ensuing the weaker NIR emission following the HT are discussed.