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

Abstract In this work, we report the near infrared and upconversion emissions of Er 3+ –Yb 3+ codoped fluorotellurite TeO 2 –ZnO–ZnF 2 glasses for different YbF 3 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 Yb 3+ and Er 3+ ions is confirmed by the temporal behavior of the near-infrared luminescence of Yb 3+ ions as well as by the enhancement of the 1532 nm emission of Er 3+ ions in the codoped samples. The Yb 3+ →Er 3+ energy transfer efficiency is calculated from the Yb 3+ lifetimes in single and codoped samples. Back transfer from Er 3+ to Yb 3+ ions is present under near infrared and visible excitation of Er 3+ 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 Yb 3+ to Er 3+ 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 YbF 3 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.