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The potassium double tungstates KGd(WO4)2, KY(WO4)2, and KLu(WO4)2 are excellent candidates for solid-state lasers, see Ref. [1] and Refs. therein, because of their high refractive index of ~2.02.1, the large transition cross-sections of rare-earth (RE) ions doped into these hosts, the possibility to incorporate very large concentrations of RE 3+ ions, reaching the stoichiometric structure KRE(WO4)2, a long inter-ionic distance of ~0.5 nm that allows for large doping concentrations without lifetime quenching, and a reasonably large thermal conductivity of ~3.3 W m -1 K -1 . These advantages have been exploited to demonstrate thin-disk lasers, broadly tunable and high-energy ultrashort-pulse lasers, and low-quantum-defect lasers.