Sensitized thulium blue and red upconversion emission and energy-transfer processes in Nd/sup 3+//Yb/sup 3+//Tm/sup 3+/-codoped PbGeO/sub 3/-based glass excited around 800 nm

This paper reports on the generation of bright blue and red upconversion luminescence through the sensitization of thulium ions in Nd/sup 3+//Yb/sup 3+//Tm/sup 3+/ triply-doped 70%XoPbGeO/sub 3/:15%PbF/sub 2/:15%CdF/sub 2/-glass excited by a diode laser source around 800 nm. The upconversion fluorescence spectra of Tm/sup 3+/ ions under 800 nm excitation is presented, for a sample codoped with Yb and a Nd/sup 3+//Yb/sup 3+//Tm/sup 3+/ triply-doped sample. It is observed that the presence of Nd/sup 3+/ in the system, produces a tenfold enhancement in the blue emission associated to the /sup 1/G/sub 4/ - /sup 3/H/sub 6/ transition of Tm/sup 3+/ ions, as compared to samples doped with Tm/sup 3+//Yb/sup 3+/. The dependence of the upconversion emission intensity as a function of the excitation power was examined and a quadratic power law behavior was obtained indicating the participation of two pump photons in the upconversion excitation mechanism. The upconversion excitation process of the Tm/sup 3+/ ion /sup 1/G/sub 4/ emitting level was achieved by an initial energy-transfer process from the 800 nm excited Nd/sup 3+/ to Yb/sup 3+/. The excited Yb/sup 3+/ then, transfer its energy to a Tm/sup 3+/ ion at the /sup 3/H/sub 4/ level excited by a pump photon at 800 nm.