Energy transfer processes in doubly doped Yb, Pr:KPb2Cl5 for mid-infrared laser applications

Mid-infrared emission at 4–5 μm, originating from the first excited state of Pr3+, was generated by means of Yb3+ sensitization in Yb, Pr:KPb2Cl5 crystals. The mechanisms involved in sensitizing Pr3+ ions were determined by studying the decay kinetics of the 2F5/2 → 2F7/2 transition of Yb3+. It was observed that emission lifetime of the 2F5/2 → 2F7/2 transition was reduced considerably from 492 μs in singly doped Yb:KPb2Cl5 to 139 μs (2 wt.% Pr) and 30 μs (5 wt.% Pr) in doubly doped Yb, Pr:KPb2Cl5 crystals. The significant reduction in the decay time of Yb3+ indicates efficient energy transfer between Yb → Pr under 970 nm excitation. Under similar experimental conditions, no 4–5 μm emission was observed from singly doped Pr:KPb2Cl5 crystal. The main energy transfer mechanisms in Yb, Pr:KPb2Cl5 were tentatively assigned to direct Yb → Pr energy transfer and Yb → Yb energy migration to distant Pr3+ ions.