Heavily Er3+-doped and Er3+/Pr3+ co-doped Gd3Ga5O12 (abbreviated as Er : GGG and Er,Pr : GGG, respectively) laser crystals were synthesized by the Czochralski method. The synthesized laser crystals were characterized by absorption, up-conversion fluorescence, near-infrared (NIR) and mid-infrared (Mid-IR) fluorescence, and luminescence decay measurements. The optical parameters related to absorption and emission cross-sections and fluorescence lifetimes were evaluated and compared. It was found that the up-conversion and NIR fluorescence weaken, at the same time Mid-IR fluorescence intensity strengthens with the increment of Er dopant concentration or co-doping with Pr3+ in Er : GGG crystals. Furthermore, the self-termination bottleneck was broken successfully in the Er,Pr : GGG crystal, and the energy transfer efficiencies of Er3+ : 4I11/2 → Pr3+ : 1G4 and Er3+ : 4I13/2 → Pr3+ : 3F4 were determined.

We report passively Q-switched ∼2 and ∼3  μm mid-infrared (MIR) solid-state lasers with a self-assembly solvothermal-synthesized Bi₂Te₃/graphene heterostructure saturable absorber (SA) for the first time. Based on the oxidation resistance and high thermal conductivity of graphene, and large modulation depth of Bi₂Te₃ nanosheets, two high-performance Q-switching lasers were realized. One is a Tm:YAP laser with a maximum average output power of 2.34 W and a pulse width of 238 ns at ∼2  μm. The corresponding maximum pulse peak power was 91 W, which was much improved in comparison with the pure graphene-based Tm laser. The other one is an Er:YSGG laser producing a pulse width of 243 ns, which is the shortest among the 2D SAs-based ∼3  μm solid-state lasers, as far as we know. Our results indicate that such a composite Bi₂Te₃/graphene material is a promising SA for generating high-performance mid-infrared pulse lasers.

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