Upconversion luminescence in Yb3+ sensitized Er3+/Yb3+-codoped tellurite glasses

A series of Er3+/Yb3+-codoped，Ho3+/Yb3+-codoped，and Er3+/Yb3+/Ho3+-triply doped tellurite glasses were prepared by high-temperature melting. Under 975nm laser light excitation，intense green and red upconversion luminescence was observed in all the three kinds of codoped tellurite glasses. The influence of Yb3+ ions on the upconversion emission properties of Er3+ and Ho3+ ions was investigated as well as the energy transfer efficiencies of Yb3+→Er3+ and Yb3+→Ho3+. Upconversion luminescence mechanisms of Er3+ and Ho3+ sensitized by Yb3+ in tellurite glasses were discussed. When the concentrations of Er3+ and Ho3+ ions were fixed at low values，the intensity of green and red upcoversion emission in Er3+/Yb3+/Ho3+-triply doped tellurite glasses increases with increasing Yb2O3 content, which are due to the interaction overlap of Er3+：4S3/2→4I15/2 and Ho3+：5S2(5F4)→5I8 transitions，Er3+：4F9/2→4I15/2 and Ho3+：5F5→5I8 transitions，respectively. In Er3+/Yb3+/Ho3+-triply doped tellurite glasses，the upconversion luminescence mechanisms were affected by the interaction energy transfers of Er3+/Yb3+, Ho3+/Yb3+ and Er3+/Ho3+. The cross-relaxation between Er3+ and Ho3+ enhances the upconversion emission intensities of Ho3+ in the visible region.