In this review we discuss processes of radiative recombination and impact ionization in light emitting structures based on bulk semiconductors, heterostructures with high potential barriers, nanostructures with deep quantum wells, as well as in nanocrystals with quantum dots. It is demonstrated that enhancement of quantum efficiency and optical power of luminescence in all of the structures under study is determined by the common physical mechanism. This mechanism is creation of additional electron-hole pairs during impact ionization process by hot carriers heated at high band offset on the heterointerface at current pumping or due to carrier multiplication in the process of multiexciton generation in nanocrystals at high-energy photons illumination.