The sensitization effects of Ni2+ on Ho3+ 3.9 μm luminescence in PbF2 single crystal

Abstract

To enhance the 3.9 μm emission of Ho:⁵I₅ → ⁵I₆ transition, this work proposes for the first time the use of Ni²⁺ as a sensitizer. Ni²⁺, Ho³⁺, and Ni²⁺/Ho³⁺ co-doped PbF₂ single crystals were grown by the Bridgman method for verification. Spectroscopic characterization confirmed the effective enhancement of Ho³⁺ emission at 3.9 μm by Ni²⁺, with the emission cross-section increasing from 0.3 × 10⁻²⁰ cm² to 0.51 × 10⁻²⁰ cm². Fluorescence lifetime measurements of the lower ⁵I₆ level revealed a Ho³⁺:⁵I₆ → Ni²⁺:³T_2g(F) energy transfer efficiency of up to 79.7%, significantly surpassing previous Nd³⁺/Ho³⁺ co-doped systems. Furthermore, simulation experiments for a 3.9 μm laser based on the Ni²⁺/Ho³⁺ co-doped PbF₂ crystal were conducted. The simulations further demonstrated the sensitization effect of Ni²⁺ on Ho³⁺ 3.9 μm emission, predicting a theoretical output energy value of 2.88 mJ under a 500 mJ pump input. Therefore, the Ni²⁺/Ho³⁺:PbF₂ single crystal is demonstrated to be a promising gain medium for 3.9 μm solid-state lasers.