The results of experimental studies of low-temperature impurity-assisted photoluminescence of n-dopedGaas/alGaas quantum well structures both in near- and far-infrared (terahertz) spectral ranges under interband optical excitation are presented. In the near-infrared photoluminescence spectra the opticalelectron transitions from the donor ground state to the hole subband are revealed. The depopulation of the impurity ground states due to these transitions allowed us to observe photoluminescence in terahertz spectralrange related to electron transitions from the first electron subband to the donor state as well as to intracenteroptical transitions. Experimental results in near- and far-infrared spectral ranges are well-consistent with the results on terahertz photoconductivity and theoretical calculations.