The optical emission and gain properties of Ga(AsSb) quantum-islands are investigate. These islands form during growth in a self-organized process in a series of Ga(AsSb)/GaAs/(AlGa)As heterostructures, resulting in an additional in-plane hole confinement of several hundreds of meV. The shape of the in-plane confinement potential is nearly parabolic and thus yields almost equidistant hole energy levels. Transmission electron microscopy reveals that the quantum islands are 100nm in diameter and exhibit an in-plane variation of the Sb concentration of more than 30 %. Up to seven bound hole states are observed in the photoluminescence spectra. Time-resolved photoluminescence data are shown as function of excitation density, lattice temperature, and excitation photon energy and reveal fast carrier capture into and relaxation within the quantum islands. Furthermore, the optical gain is measured using the variable stripe-length method and the advantages of such structures as active laser material are discussed.