The optical properties of silicon quantum dots (QDs) embedded in a SiO₂ matrix are investigated at various temperatures using photoluminescence (PL) and time-resolved photoluminescence. Two broad luminescence bands, the S-band located at 600–850 nm and the F-band located at 450–600 nm, are observed. In the S-band a stretched exponential time evolution is observed and the short wavelengths have significantly shorter lifetimes than the long wavelengths. In the low temperature regime, the process of carrier delocalization from the defect states and capture into the QDs is dominant, which results in a decrease in PL intensity from the F-band and an increase from the S-band. In the high temperature regime, the carriers captured into the QDs decrease due to competition between the defect states, which results in a PL intensity decrease for both bands. The PL intensity on the high energy side of the S-band decreases more strongly than that on the low energy side due to the state filling effect, which results in a 30 nm red shift. The S-band is attributed mainly to zero-phonon electron–hole recombination due to enhancement of the quantum confinement effect. The F-band has a single exponential evolution with a much shorter lifetime of nanoseconds and is attributed to defect states of silicon oxide.