Near and Mid-Infrared Emission Characteristics of Er³⁺/Tm³⁺/Ho³⁺-Doped LiYF₄ Single Crystals Excited by Laser Diode.

Yttrium lithium fluoride (LiYF₄) single crystals triply doped with Er³⁺/Tm³⁺/Ho³⁺ are synthesized by a vertical Bridgman method. Absorption spectra, emission spectra, and decay curves are measured to investigate the luminescent properties of the crystals. Compared with Er³⁺ singly doped and Er³⁺/Tm³⁺ and Er³⁺/Ho³⁺ doubly doped LiYF₄ crystals, an intense emission around 2.7 µm can be obtained in the triply doped LiYF4 crystal under excitation of 980 nm laser diode. Meanwhile, the near infrared emission at 1.5 µm from Er³⁺ in the triply doped crystal is effectively reduced. The possible energy transfer processes and the luminescent mechanisms for enhancing emission at 2.7 µm and quenching emission at 1.5 µm in the Er³⁺/Ho³⁺/Tm³⁺ triply doped crystals are proposed. The large energy transfer efficiency of 82.0% and excellent optical transmission indicate that this Er³⁺/Tm³⁺/Ho³⁺ triply doped crystal can be considered as a promising material for a mid- infrared laser at 2.7 µm.