Optical properties, fluorescence mechanisms and energy transfer in Tm3+, Ho3+ and Tm3+-Ho3+ doped near-infrared laser glasses, sensitized by Yb3+

The optical properties of the rare elements Tm3+, Ho3+ and Yb3+ were systematically investigated in various glasses. The Tm3+ doped aluminozircofluoride glass shows higher quantum efficiency, longer lifetime and stronger fluorescence intensity than Tm3+ doped YSGG crystal and other Tm3+ doped glasses for the H-3(4) --> H-3(6) transition. Similar quantum efficiency, longer lifetime and stronger fluorescence intensity were also found in Ho3+ doped aluminozircofluoride glass for the I-5(7) --> I-5(8) transition. The higher quantum efficiencies of Tm3+ and Ho3+ in aluminozircofluoride glass are due to the longer lifetime and the lower phonon energy. The fluorescence mechanisms and energy transfer in the Yb3+-Tm3+ system, Yb3+-Ho3+ system and Yb3+ Tm3+-Ho3+ system were studied. The very strong fluorescence intensities in the Yb3+-Tm3+ system for Tm3+ and the Yb3+-Tm3+-Ho3+ system for Ho3+ which are 1.68 times that of Tm3+ doped YSGG crystal and 2.25 times that of Tm3+-Ho3+ codoped YSGG crystal are attributed to the efficient Yb3+ --> Tm3+, Yb3+ --> Ho3+ and Tm3+ --> Ho3+ energy transfer processes. The fluorescence processes are described by cross relaxations of F-2(5/2) --> H-3(5) --> H-3(4) --> H-3(6) --> F-2(7/2) and F-2(5/2) --> H-3(5) (or F-2(5/2) --> I-5(6) --> H-3(5)) --> H-3(4) --> I-5(7) --> I-5(8) --> H-3(6) --> F-2(7/2).