Abstract: The GaAs_1-ySb_y/GaAs quantum well is one of the most promising active materials for 1.3 μm vertical-cavity surface-emitting lasers grown on GaAs. This work focuses on the determination of the band alignment, bandgap bowing parameters, temperature dependent characteristics, and the spontaneous recombination lifetimes for GaAs_1-ySb_y/GaAs quantum well structures. To fulfill these tasks, a novel and robust method, variable barrier spectroscopy, is proposed. Two sets of samples with different harrier configurations are grown by molecular beam epitaxy. The optical spectroscopy combining with the theoretical calculations reveals that a considerable amount (58%) of the -1.58 eV bandgap bowing being distributed to the conduction band. As a suitable active material for 1.3 μm emission, pseudomorphic GaAs _0.643Sb_0.357 grown on GaAs is determined to have a weak type-I conduction band offset over the entire temperature range, with conduction band offset of 4.5 ± 23.8 meV at 0 K and 23 ± 23 meV at 300 K. The spontaneous recombination lifetimes are determined in the range of 2.0 ∼ 3.2 ns for the samples at 12 K using time-resolved photoluminescence. The luminescence refrigeration in semiconductors has attracted widespread interest and has become a new and active area of research. Another aim of this dissertation involves the theoretical investigation of the cooling characteristics in semiconductor luminescence refrigeration. To fulfill this task, a model that takes into account photon recycling and the rate equations for both carriers and photons is used to do the analysis. General expressions for cooling efficiency, cooling power density, and internal quantum efficiency and extraction efficiency required to achieve net cooling can then be derived. The boundaries for luminescence refrigeration are defined for the case where the absorption of recycled photons is spectrally uniform across the luminescence linewidth. The cooling characteristics are evaluated for the photoluminescence refrigeration in an intrinsic GaAs slab as well as the electroluminescence refrigeration in an AlGaAs/GaAs/AlGaAs double-heterojunction light emitting diode, which shows that cooling is accessible when the extraction and internal quantum efficiency are sufficiently high.