Down-conversion process in Tb3+-Yb3+ co-doped Calibo glasses

► The down-conversion process was observed for the first time in Tb3+-Yb3+ co-doped Calibo glasses. ► Excitation power measurements allowed identification of the one-photon process in the energy transfer from Tb3+ to Yb3+. ► An enhanced near-infrared emission was observed from Yb3+ with almost 32% for the energy transfer efficiency. ► Tb3+-Yb3+ cross-relaxation and multiphonon decay processes explain all these results. ► This system has potential application as a down-converter material for the near-infrared region.