Structural, optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO2–ZnO–ZnF2 glasses. ErF3 nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the 4I13/2 → 4I15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω2 parameter, as compared to the glass, confirm the presence of Er3+ ions in a crystalline environment in glass-ceramic samples. The analysis of the 4I13/2 decays suggests that a fraction of Er3+ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the 4F9/2 → 4I15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.