The work considers the methods for increasing the intensity of low temperature terahertz luminescence in semiconductor structures with bulk epitaxial n-GaAs layers doped with silicon donors under interband optical pumping. Such  an increase can be realized due to the accelerated depopulation of the ground impurity level by stimulated near-infrared radiation, which is created in the same structure. Stimulated interband emission was induced by a total internal  reflection optical resonator. Samples were investigated by measuring the near-infrared photoluminescence and terahertz photoluminescence at liquid helium temperature. Impurity-assisted near-infrared spontaneous and stimulated photoluminescence and their dependences on optical pumping power was demonstrated. Impurity-assisted generation of terahertz radiation was observed in further intention to investigate the influence of near-infrared stimulated emission on it. Obtained results can be used in the development of new semiconductor terahertz emitters.