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The spectral properties of lightly doped Er:CaF 2 and Er,Pr:CaF 2 single crystals were investigated. Benefited from particular clustering effect, 2.79 μm continuous-wave (CW) laser operation was demonstrated in lightly doped 3 at.% Er:CaF 2 crystal. After co-doping small amount of Pr 3+ , the lifetime gap between Er 3+ : 4 I 11/2 and Er 3+ : 4 I 13/2 was shortened from 7.86 ms to about 1 ms. Moreover, the near-infrared and up-conversion fluorescence were significantly quenched. Thus, the CW laser performance was greatly improved. The slope efficiency was effectively improved from 8.0% to 15.8%. [ABSTRACT FROM AUTHOR]

• After co-doping Tb3+ ions, the Ω4/Ω6 increased 1.57 from to 1.66. • The branching ratios of the 3H 4 →3F 4 transition also strengthened. • The decay curve of 3F 4 level doped with different Tb3+ ions concentration decreased. • Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. Tm3+ and Tb3+ co-doped Y 3 Al 5 O 12 (YAG) ceramics were fabricated by high temperature solid state reaction under oxygen sintering. The absorption spectra, fluorescence spectra and fluorescence decay curves of Tm,Tb:YAG ceramics were measured. The spectral parameters of Tm,Tb:YAG ceramic were calculated. The lifetimes of Tm3+:3F 4 level of Tm,Tb:YAG ceramics were calculated to be 11.28, 2.12, 1.24, 0.63 and 0.49 ms for the Tb3+ doping concentration of 0, 0.1, 0.2, 0.35 at 0.5 at%, respectively. The co-doping Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. These results indicate that the addition of Tb3+ ions in Tm,Tb:YAG ceramic could be a promising technique for laser operation around 1.5 µm. [ABSTRACT FROM AUTHOR]