It is demonstrated that capping InAs self-assembled quantum dots with a thin GaAsSb layer allows the emission to be extended beyond 1.5 um at room temperature. This behaviour is attributed to the formation of a type-II system for Sb composition above -15%. Magneto-optical spectroscopy suggests that the type-II excitons remain compact and it is postulated that strain modulation of the GaAsSb layer results in hole localization immediately above the quantum dots.