Optical characterization of a strained GaAs0.64Sb0.36/GaAs and a strain-compensated GaAs0.64Sb0.36/GaAs0.79P0.21 triple quantum well (TQW) structures grown by metal organic vapor phase epitaxy has been carried out by using photoreflectance (PR), surface photovoltage spectroscopy (SPS) and photoluminescence (PL) techniques. For the GaAs0.64Sb0.36/GaAs TQW, only a very weak PR feature was observed in the vicinity of fundamental transition. A large blueshift of the peak position of PL feature of the sample at low temperature with increasing of excitation power density has been attributed to a weakly type-II heterojunction formed between GaAs0.64Sb0.36 and GaAs. The PR and surface photovoltage spectra of GaAs0.64Sb0.36/GaAs0.79P0.21 TQW display a series of features originated from interband transitions which is a typical characteristic of type-I QW structure. In order to identify the interband transitions, a calculation was performed based on the envelope function approximation using the conduction band-offset Q(c) and strain compensation factor gamma as adjustable parameters. Good agreement between experimental results and theoretical calculation is achieved by taking Q(c) = 0.30 +/- 0.05 and gamma = 0.60 +/- 0.05. The results indicate that the energy band of the strain-compensated QW structure is significantly influenced by replacing GaAs barrier by GaAs0.79P0.21 layers, which changes the weakly type-II to a type-I structure. The strain-compensated GaAs0.64Sb0.36/GaAs0.79P0.21 TQW has a larger overlap integral and hence a higher transition probability, providing a possibility for fabricating high efficiency near infrared laser diodes. (c) 2012 Elsevier B.V. All rights reserved.