We present a detailed characterization of energy transfer processes in Er 3ϩ -doped and Er 3ϩ ,Pr 3ϩ -codoped ZBLAN bulk glasses. For several Er 3ϩ ͑0.25-8.75 mol%͒ and Pr 3ϩ ͑0.25-1.55 mol%͒ concentrations, we investigate energy transfer upconversion ͑ETU͒ and cross relaxation in Er 3ϩ as well as energy transfer ͑ET͒ from Er 3ϩ to the Pr 3ϩ codopant. The measured parameters of ETU from the Er 3ϩ 4 I 13/2 and 4 I 11/2 levels are comparable to those of LiYF 4 :Er 3ϩ . ETU from 4 I 13/2 , in particular, possesses a factor of 3 larger probability than ETU from 4 I 11/2 . The parameters of ET from the Er 3ϩ 4 I 13/2 and 4 I 11/2 levels to the Pr 3ϩ codopant are larger than the corresponding ETU parameters. ET effectively quenches the 4 I 13/2 intrinsic lifetime of 9 ms down to 20 s for the highest Er 3ϩ and Pr 3ϩ concentrations investigated, and is more efficient than ET from 4 I 11/2 , because the corresponding absorption transition in Pr 3ϩ has a large oscillator strength and back transfer is inhibited by fast multiphonon relaxation from the corresponding Pr 3ϩ level. In both cases, the ET parameters depend on Er 3ϩ concentration in a similar way as the ETU parameters but depend only weakly on Pr 3ϩ concentration. This shows that energy migration within the Er 3ϩ 4 I 13/2 and 4 I 11/2 levels is fast. The presented results are important for the choice of the appropriate operational regime of the erbium 3-m fiber laser.

A detailed characterization of energy level lifetimes and energy-transfer processes in Er3+-doped and Er3+, Pr3+-codoped ZBLAN bulk glasses is presented. Energy transfer upconversion parameters from the Er3+ 4I13/2 and 4I11/2 levels have been measured and are compared to energy transfer from Er3+ to a Pr3+ codopant. To assess the practicality of energy transfer a high power, diode pumped, 3 μm, Er3+, Pr3+-codoped ZBLAN fiber laser is presented.

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