The oxidation and passivation of freshly prepared silicon nanocrystals Si NCs have been studied by exciting them with a low-fluence violet laser at 406 nm and measuring both the heat generated by nonradiative transitions and the photoluminescence PL resulting from radiative charge carrier recombination over a period of 31 days. Laser-induced deflection was employed as a sensitive tool to determine the heat transferred to the phonon bath. The PL quantum efficiency of Si NCs passivated in air was found to develop with a time constant of 8 d from zero to a terminal saturation value of approximately 65%.