Up-Conversion emission in Er-Yb doped transparent oxy uoride nano-glass-ceramics

Abstract

Oxyfluoride glass-ceramics have become increasingly important in the last decades because they combine the advantages of glass processing with the good crystalline properties, such as good mechanical, thermal and optical ones. From the pioneering work of Wang and Ohwaki in 1993, concerning the e cient green and red Up-Conversion (UC) emission in Er3+-Yb3+ doped GCs containing PbxCd1-xF2 nano-crystals (NCs), many fluoride crystal phases have been studied, showing the possibility to e ectively improve the luminescence of Rare-Earth ions (REI) when they are embedded in fluoride NCs. LnF3 [2] or RLnF4 [3] (R= K, Na, Li) crystals phases are especially important because the similar size of ions crystals former and the other REI used as dopants allows their incorporation into the crystals phase. In these work, two oxyfluoride compositions doped with 0.5Er and co-doped with 2 and 4Yb (mol %) have been studied. A structural study, performed by XRD, showed the precipitation of LaF3 or NaGdF4 nano-crystals in the glass. HR-TEM and XANES techniques have allowed evidencing the Er3+ and Yb3+ enrichment in the nano-crystals and estimating their concentration in the crystal phase. Optical measurements of Er3+ singly doped and Yb3+ co-doped samples showed UC emission (green and red) upon NIR excitation at 980 nm. A notable improve in the UC emission intensity is observed from glasses to GCs and the two-photon origin of the process was proved. Moreover, the green/red ratio of the UC emission changes with the heat treatment of GCs and a possible explication related to the REI concentration is given.