Spectroscopic properties of ytterbium, praseodymium-codoped fluorozirconate glass for laser emission at 36 μm

Excitation of the F27/2→F25/2 transition of the Yb3+ ion in Yb3+, Pr3+-doped fluorozirconate glass at 974 nm results in efficient excitation of the G41 level of Pr3+ ion that in turn emits in the middle infrared at ∼3.6 μm. The energy transfer (ET) process Yb3+(F25/2)→Pr3+(G41) is assisted by fast excitation migration among the Yb3+ ions. An upconversion process involving ET from the F25/2 level to the G41 excited state populates the P03 excited state that produces emission at 481, 521, 603, 636, and 717 nm. A study of the behavior of the fluorescence from the G41 level at 1325 nm and from the P03 level at 603 nm allowed the estimation of the ET rate constants for the processes involved after short-pulsed laser excitation at 974 nm. A rate-equation model was employed to evaluate the population inversion relating to the G41→F43 transition of the Pr3+ ion at 3.6 μm under continuous wave pumping.