Selective sensitization of 480-nm blue upconversion by Tm3+-Er3+ energy transfer in tellurite glass

Abstract

Blue upconversion luminescence at 480 nm resulting from Tm3+:1G4 → 3H6 by 650-nm pumping was selectively sensitized with Er3+ codoped in a tellurite glass. Codoping of Er3+ also quenched the 1D2 → 3F4 luminescence at 450 nm, leading to a single-line blue upconversion. To investigate this sensitized upconversion mechanism, the excitation spectra and the concentration dependence of the lifetimes of the Tm3+ and the Er3+ levels were measured for various doping levels. The Tm3+:3H4 level, which is the intermediate level of excited-state absorption to 1D2, to was found to be depopulated by the energy transfer of Tm3+:3H4 → Er3+:4I9/2 and the Tm3+:3F4 level, which is the intermediate level of excited-state absorption to 1G4, was found to be sensitized by the Er3+:4I13/2 → Tm3+:4F4 energy transfer. The concentration dependence of the transfer rate and of the efficiency of related levels was obtained, and it was concluded that the codoped Er3+ ion is a selective sensitizer in terms of quenching 1D2 upconversion and activating 1G4 upconversion by acting as an acceptor or as a donor for the initial level of each excited-state absorption of the Tm3+ ion.