The low-temperature terahertz and near-infrared photoluminescence from the near-infrared laser nanostructure with GaAs/AlGaAs quantum wells doped with shallow donors is studied under intense interband optical excitation. The optical electron transitions involving excited and ground donor states in quantum wells are revealed in terahertz and near-infrared photoluminescence spectra. Impurity assisted near-infrared stimulated emission under interband optical pumping and its influence on the terahertz optical electron transitions are observed and investigated. It is demonstrated, that at the various pumping levels the competition between different impurity assisted stimulated optical transitions in the near-infrared range leads to appearance of the different impurity related emission lines in terahertz spectra.