The effects of a thin GaAsSb strain-reducing layer on the optical properties of InAs/GaAs quantum dots (QDs) are investigated. With increasing Sb composition, the room-temperature emission wavelength of the InAs QDs increases to ∼1.43 μm. For Sb compositions above 14%, the system becomes Type II, with a decrease of the photoluminescence (PL) efficiency. At a composition of 14%, the room-temperature PL efficiency is maximized, and is also significantly enhanced when compared to that of conventional InGaAs-capped InAs QDs grown under the same conditions. Room-temperature ground-state lasing at 1.292 μm is demonstrated for an InAs/GaAsSb/GaAs structure.