This work is focused on examining ultrafast photoluminescent properties of InAs quantum dots (QDs) grown on GaAs substrate and covered by GaAs1-xSbx strain reducing capping layer (SRL). The samples were prepared by Stranski-Krastanow growth method. The aim is to understand the processes occurring inside the QDs and wetting layer (WL) and how the SRL influences the energy levels inside the QDs. It was already proven that the SRL of this composition can decrease energies of transitions inside these QDs to the IR range, which makes these structures promising candidate for devices emitting near infrared radiation. It is possible to shift the luminescence wavelength towards 1.3 and even 1.55 μm, which are widely used in telecommunications. Using upconversion method we measured luminescence dynamics of two samples with different concentration of Sb in the SRL with sub-picosecond time resolution. We investigated the effect of temperature, as well as the intensity and wavelength of the excitation pulse. We also compared the properties of the samples after excitation by λ=760 nm pulse and 850 nm pulse – the former one is energetically above the GaAs substrate band gap; in the second case we excited only the QDs and the WL. We consequently derived recombination and relaxation processes occurring inside InAs QDs and also proved that the transport of charge carriers from the substrate and from the WL into the QDs is efficient.