Tm3+-activated transparent oxy-fluoride glass–ceramics: structural and spectroscopic properties

Ultra-transparent glass–ceramics activated with thulium ions were fabricated employing different heat treatments of precursor oxy-fluoride glass. The spectroscopic properties of the thulium ions, studied through UV–Vis–NIR absorption and luminescence spectroscopy, showed that most of the active ions were embedded in the crystalline phase. The size of nucleated nanocrystals, controlled by the temperature and time of annealing and measured by low-frequency-Raman spectroscopy, was found to range from 7 to 18 nm. From the absorption measurement we extracted the cross-sections of Tm3+ ions embedded in the crystalline and glassy phases. Judd–Ofelt analysis was carried out on precursor glass and crystal. Comparing calculated and experimental lifetimes, before and after the heat treatment procedure, we found that the ceramming increases the quantum efficiency of the Tm3+ electronic transitions.