Cooperative energy transfer in Tb 3+/Yb 3+- and Nd 3+/Yb 3+/Tb 3+-codoped oxyfluoride glasses

Abstract

This paper reports on cooperative energy transfer and upconversion luminescence properties of Tb 3+/Yb 3+- and Nd 3+/Yb 3+/Tb 3+-codoped oxyfluoride glasses. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence along with weak ultraviolet (UV)–visible emissions has been observed in Yb 3+/Tb 3+-codoped oxyfluoride glasses. Power dependence of UV–visible upconversion luminescence intensity has been examined, revealing that a cooperative energy transfer mechanism from Yb 3+ ions is responsible for the excitation of Tb 3+ ions. Meanwhile, it is noticed that Tb 3+ upconversion emission bands have also been clearly detected at 487, 542, 587 and 620 nm in Nd 3+/Yb 3+/Tb 3+-codoped oxyfluoride glasses upon excitation with a 808 nm laser diode. The quadratic dependence of the upconversion luminescence on the pump-laser power indicates two-photon process for the population of Tb 3+: 5D 4 state via Nd 3+→Yb 3+→Tb 3+ energy transfer. However, no emission has been observed in the oxyfluoride glasses codoped with Yb 3+/Tb 3+ or Nd 3+/Tb 3+, respectively, upon excited at a 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd 3+ to Yb 3+, and then a cooperative energy transfer process from two excited Yb 3+ to Tb 3+ has been presented.