Down- and up-conversion emissions in Er3+-Yb3+ codoped TeO2-ZnO-ZnF2 glasses

In this work, we report the near infrared and upconversion emissions of Er3+-Yb3+ codoped fluorotellurite TeO2-ZnO-ZnF2 glasses for different YbF3 concentrations ranging between 0.5 and 2 wt%. The study includes absorption and emission spectra and lifetime measurements for the infrared and visible fluorescence. The energy transfer between Yb3+ and Er3+ ions is confirmed by the temporal behavior of the near-infrared luminescence of Yb3+ ions as well as by the enhancement of the 1532 nm emission of Er3+ ions in the codoped samples. The Yb3+→Er3+ energy transfer efficiency is calculated from the Yb3+ lifetimes in single and codoped samples. Back transfer from Er3+ to Yb3+ ions is present under near infrared and visible excitation of Er3+ ions at 798 and 488 nm respectively. An enhancement of the visible upconversion fluorescence is also observed in the codoped samples due to energy transfer from Yb3+ to Er3+ ions. The standardized value for the efficiency of the green upconversion emission is 1.06×10−4 for the codoped sample with 2 wt% of YbF3 which is comparable to that reported in lead-zinc-tellurite glasses. The possible upconversion processes and mechanisms leading to the population of several excited levels are discussed.