Spectroscopic properties of ytterbium, praseodymium-codoped fluorozirconate glass for laser emission at 3.6 μm

Excitation of the ²F_7/2 → ²F _5/2 transition of the Yb³⁺ ion in Yb³⁺, Pr ³⁺-doped fluorozirconate glass at 974 nm results in efficient excitation of the ¹G₄ level of Pr³⁺ ion that in turn emits in the middle infrared at ∼3.6 μm. The energy transfer (ET) process Yb³⁺(²F_5/2) → Pr ³⁺(¹G₄) is assisted by fast excitation migration among the Yb³⁺ ions. An upconversion process involving ET from the ²F_5/2 level to the ¹G₄ excited state populates the ³P₀ excited state that produces emission at 481, 521, 603, 636, and 717 nm. A study of the behavior of the fluorescence from the ¹G₄ level at 1325 nm and from the ³P₀ 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 ¹G₄ → ³F₄ transition of the Pr³⁺ ion at 3.6 μm under continuous wave pumping.