Infrared-to-red upconversion luminescence in samarium-doped antimony glasses

A new antimony-based glass system (K2O–B2O3–Sb2O3) having low phonon energy (about 600 cm−1) doped with Sm3+ ions has been developed. Infrared reflection spectroscopic (IRRS) studies have been employed to establish its low phonon energy. Ultraviolet–Visible–near infrared (UV–Vis–NIR) absorption and photoluminescence upconversion properties with the spectrochemistry of the 15K2O–15B2O3–70Sb2O3 (mol%) glasses have been studied doping with different concentrations (0.1–1.0 wt%) of Sm2O3. UV–Vis–NIR absorption band positions have been justified with quantitative calculation of nephelauxetic parameter and covalent bonding characteristics of the host. NIR to visible upconversion has been investigated by exciting at 949 nm at room temperature. Three upconverted bands originating from the 4G5/2→6H5/2, 4G5/2→6H7/2 and 4G5/2→6H9/2 transitions are found to be centered at 566 (green, weak), 602 (orange, weak) and 636 (red, remarkably strong) nm, respectively. These bands have been explained from the evaluation of the absorption, normal (downconversion) fluorescence and excitation spectra. The upconversion processes have been explained by the excited state absorption (ESA), energy transfer (ET) and cross-relaxation (CR) mechanisms involving population of the metastable (storage) energy level (4G5/2) by multiphonon deexcitation effect. It is evident from the IRRS study that the upconversion phenomena are expedited by the low multiphonon relaxation rate in antimony glasses owing to their low phonon energy (602 cm−1, the main and highest intensity Sb–O–Sb stretching band) which is very close to that of fluoride glasses (500–600 cm−1).