Wide wavelength range of upconversion fluorescence at 360 nm, 450 nm, 475 nm, 647 nm, and 800 nm were observed in Tm3+ and Yb3+ codoped ZBLAN glass when pumped by a laser diode at approximately 970 nm. Those emissions are from three metastable states 1D2, 1G4 and 3F4, respectively. Three samples with varying Tm3+ and Yb3+ ion doping were investigated. It was shown that the luminescence intensity, as well as the dependence of intensity on laser power density, vary strongly with rare earth ion concentrations. And the mechanism for the population of 1D2 level is clarified further.
|