Hydrogenated silicon nitride (SiNx:H) thin films are deposited on p-type silicon substrates by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of ammonia and silane at 230 °C. The chemical compositions and optical properties of these films, which are dealt at different annealing temperatures, are investigated by Fourier transform infrared (FTIR) absorption spectroscopy and photoluminescence (PL) spectroscopy, respectively. It is shown that the FTIR presents an asymmetric Si-N stretching mode, whose magnitude is enhanced and position is shifted towards higher frequencies gradually with the increase of the annealing temperature. Meanwhile, it is found that the PL peak shows red shift with its magnitude decreasing, and disappears at 1100 °C. The FTIR and PL spectra characteristics suggest that the light emission is attributed to the quantum confinement effect of the carriers inside silicon quantum dots embedded in SiNx: H thin films.