Energy transfer processes in Er3+-doped and Er3+,Pr3+-codoped ZBLAN glasses

We present a detailed characterization of energy transfer processes in Er3-doped and Er3+,Pr3+-codoped ZBLAN bulk glasses. For several Er3+ (0.25-8.7 5 mol%) and Pr3+ (0.25-1.55 mol%) concentrations, we investigate energy tra nsfer upconversion (ETU) and cross relaxation in Er3+ as well as energy tra nsfer (ET) from Er3+ to the Pr3+ codopant. The measured parameters of ETU f rom the Er3+ I-4(13/2) and I-4(11/2) levels are comparable to those of LiYF 4:Er3+. ETU from I-4(13/2), in particular, possesses a factor of 3 larger p robability than ETU from I-4(11/2). The parameters of ET from the Er3+ I-4( 13/2) and I-4(11/2) levels to the Pr3+ codopant are larger than the corresp onding ETU parameters. ET effectively quenches the I-4(13/2) intrinsic life time of 9 ms down to 20 mu s for the highest Er3+ and Pr3+ concentrations i nvestigated, and is more efficient than ET from I-4(11/2), because the corr esponding absorption transition in Pr3+ has a large oscillator strength and back transfer is inhibited by fast multiphonon relaxation from the corresp onding Pr3+ level. In both cases, the ET parameters depend on Er3+ concentr ation in a similar way as the ETU parameters but depend only weakly on Pr3 concentration. This shows that energy migration within the Er3+ I-4(13/2) and I-4(11/2) levels is fast. The presented results are important for the c hoice of the appropriate operational regime of the erbium 3-mu m fiber lase r.