Mechanisms and concentration dependence of Tm3+ blue and Er3+ green up-conversion in codoped glasses by red-laser pumping

Abstract Tm3+-Er3+ codoped tellurite glasses were pumped at 650 nm and the up-conversion characteristics of Tm3+ and Er3+ luminescences were investigated. By Er3+ codoping, the Tm3+-460 nm up-conversion luminescence due to the 1D2→3F4 transition was quenched and the Tm3+-480 nm up-conversion luminescence due to the 1G4→3H6 transition was selectively sensitized, due to which the intensity became more than 20 times larger than in the absence of Er3+. Both Tm3+-480 nm and Er3+-550 nm up-conversion luminescence intensities have a maximum in the range where the ratio of Er3+- to Tm3+-content is about two. The result was discussed in the context of the energy transfer efficiency calculated from the lifetime of the Er3+:4I 13 2 level, the competition between the excited state absorption efficiency of Tm3+:1G4←3F4 and the ground state absorption of Er3+:4F 9 2 ←4I 15 2 estimated from the Judd-Ofelt analyses, and the concentration quenching of the Er3+:4S 3 2 level, mainly due to the cross relaxation. It is concluded that the small optimum ratio of the donor- to acceptor-content (≅2) should be ascribed to the specific mechanisms in the present sensitized up-conversion.