Effective sensitization of Dy³⁺:⁶H_11/2 energy level by Tm³⁺ ions in KPb₂Br₅ crystal for 4.3 µm lasers

To the best of our knowledge, this is the first study to investigate the use of Tm³⁺ to sensitize the Dy³⁺ ion and enhance the ∼4.3 µm emission from Dy³⁺:⁶H_11/2 → ⁶H_13/2 in the KPb₂Br₅ (KPB) crystal. The ∼4.3 µm fluorescence emission properties and energy transfer mechanism of the Dy:KPB and Tm,Dy:KPB crystals were examined. The results show that Tm³⁺ is an excellent sensitizer to the Dy³⁺ ion and can provide an efficient excitation channel; thus, the Tm,Dy:KPB crystal can be pumped by a commercial 808 nm laser diode (LD). Compared with the Dy:KPB crystal, co-doping with the Tm³⁺ ion improves the absorption around 800 nm by an order of magnitude, and the energy transfer efficiency from Tm³⁺:³F₄ to Dy³⁺:⁶H_11/2 is as high as 76.7%, indicating that the Tm,Dy:KPB crystal has great potential application in ∼4.3 µm mid-infrared lasers under a commercial LD pump.