Energy transfer processes in doubly doped Yb, Pr:KPb 2Cl 5 for mid-infrared laser applications

Abstract

Mid-infrared emission at 4–5 μm, originating from the first excited state of Pr 3+, was generated by means of Yb 3+ sensitization in Yb, Pr:KPb 2Cl 5 crystals. The mechanisms involved in sensitizing Pr 3+ ions were determined by studying the decay kinetics of the 2F 5/2 → 2F 7/2 transition of Yb 3+. It was observed that emission lifetime of the 2F 5/2 → 2F 7/2 transition was reduced considerably from 492 μs in singly doped Yb:KPb 2Cl 5 to 139 μs (2 wt.% Pr) and 30 μs (5 wt.% Pr) in doubly doped Yb, Pr:KPb 2Cl 5 crystals. The significant reduction in the decay time of Yb 3+ 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:KPb 2Cl 5 crystal. The main energy transfer mechanisms in Yb, Pr:KPb 2Cl 5 were tentatively assigned to direct Yb → Pr energy transfer and Yb → Yb energy migration to distant Pr 3+ ions.