The photoluminescence and stimulated emission during interband transitions in quantum wells based on HgCdTe placed in an insulator waveguide based on a wide-gap CdHgTe alloy are studied. Heterostructures with quantum wells based on HgCdTe are of interest for the development of long-wavelength lasers in the range of 25–60 μm, which is currently unattainable for quantum-cascade lasers. Optimal designs of quantum wells for attainment of long-wavelength stimulated emission under optical pumping are discussed. It is shown that narrow quantum wells from pure HgTe appear to be more promising for long-wavelength lasers in comparison with wide (potential) wells from the alloy due to the suppression of Auger recombination. It is demonstrated that molecular-beam epitaxy makes it possible to obtain structures for the localization of radiation with a wavelength of up to 25 μm at a high growth rate. Stimulated emission is obtained for wavelengths of 14–6 μm with a threshold pump intensity in the range of 100–500 W/cm2 at 20 K.