UV-stimulated near-IR emission of Pr3+ in phosphate glass via twofold-coordinated Sn centers

The optical properties of Pr2O3 and SnO co-doped barium–phosphate glass prepared by the melt-quenching technique have been investigated. Optical absorption and X-ray photoelectron spectroscopy (XPS) are employed in the characterization of tin species. The prevalence of divalent tin is indicated by the XPS data in accord with a conspicuous absorption band detected around 287 nm ascribed to twofold-coordinated Sn centers (isoelectronic with Sn2+). Upon ultraviolet (UV) photoexcitation of the tin centers, near-infrared (IR) emission from Pr3+ ions is realized. An excitation spectrum acquired by monitoring Pr3+ emission from the 1D2 state at 1.03 μm revealed a broad band around 290 nm consistent with a SnPr donor–acceptor energy transfer channel. The data supports a mechanism starting with the singlet-to-singlet UV excitation of Sn centers, followed by the intersystem crossing populating their triplet states emitting in the visible. From these, energy transfer occurs to 3P0, 3P1, 1I6, and 3P2 resonant states in Pr3+, from which the near-IR emitting states 1D2 and 1G4 are populated.