Size dependent optical properties of Si quantum dots in Si-rich nitride/Si3N4 superlattice synthesized by magnetron sputteringWe report on the radiative cooling of an indirect band gap semiconductor through its absorption of interband incoherent light and subsequent spontaneous emission of multiple longer-wavelength photons ͑optical down-conversion͒ in conditions when the energy deficit of the process is covered by the thermal energy. The 10ϫ 10ϫ 5 mm 3 Si slab kept at 473 K in an evacuated up to 10 −3 torr chamber was cooled by 3.8 K when pumped with light of 1.06 m wavelength. First-principles estimates and several advantages of the down-conversion approach over possible cooling of direct band gap semiconductors through the optical upconversion and negative luminescence are discussed.