Powerful 1.2-µm laser operation was produced in Ho³⁺-doped single-cladding, in-house fabricated ZrF₄-BaF₂-YF₃-AlF₃ (ZBYA) glass fibers. The fibers were fabricated based on ZBYA glass with a composition of ZrF₄-BaF₂-YF₃-AlF₃. Pumped by an 1150-nm Raman fiber laser, the maximum combined laser output power emitted from both sides of a 0.5-mol% Ho³⁺-doped ZBYA fiber was 6.7 W, with a slope efficiency of 40.5%. We also observed lasing at 2.9 µm with an output power of 350 mW, which was ascribed to the transition of Ho³⁺:⁵I₆ → ⁵I₇. The effect of rare earth (RE) doping concentration and the length of the gain fiber were also investigated to determine their effect on laser performance at 1.2 µm and 2.9 µm.