We present a detailed characterization of energy transfer processes in Er3+-doped and Er3+,Pr3+-codoped ZBLAN bulk glasses. For several Er3+ (0.25-8.75 mol%) and Pr3+ (0.25-1.55 mol%) concentrations, we investigate energy transfer upconversion (ETU) and cross relaxation in Er3+ as well as energy transfer (ET) from Er3+ to the Pr3+ codopant. The measured parameters of ETU from the Er3+ 4I13/2 and 4I11/2 levels are comparable to those of LiYF4:Er3+. ETU from 4I13/2, in particular, possesses a factor of 3 larger probability than ETU from 4I11/2. The parameters of ET from the Er3+ 4I13/2 and 4I11/2 levels to the Pr3+ codopant are larger than the corresponding ETU parameters. ET effectively quenches the 4I13/2 intrinsic lifetime of 9 ms down to 20 μs for the highest Er3+ and Pr3+ concentrations investigated, and is more efficient than ET from 4I11/2, because the corresponding absorption transition in Pr3+ has a large oscillator strength and back transfer is inhibited by fast multiphonon relaxation from the corresponding Pr3+ level. In both cases, the ET parameters depend on Er3+ concentration in a similar way as the ETU parameters but depend only weakly on Pr3+ concentration. This shows that energy migration within the Er3+ 4I13/2 and 4I11/2 levels is fast. The presented results are important for the choice of the appropriate operational regime of the erbium 3-μm fiber laser.
|Number of pages
|Physical Review B: Condensed Matter and Materials Physics
|Published - 2000