Superlattices of Si 3 N 4 and Si-rich silicon nitride thin layers with varying thickness were prepared by plasma enhanced chemical vapor deposition. After high temperature annealing, Si nanocrystals were formed in the former Si-rich nitride layers. The control of the Si quantum dots size via the SiN x layer thickness was confirmed by transmission electron microscopy. The size of the nanocrystals was well in agreement with the former thickness of the respective Si-rich silicon nitride layers. In addition X-ray diffraction evidenced that the Si quantum dots are crystalline whereas the Si 3 N 4 matrix remains amorphous even after annealing at 1200 C. Despite the proven Si nanocrystals formation with controlled sizes, the photoluminescence was 2 orders of magnitude weaker than for Si nanocrystals in SiO 2 matrix. Also, a systematic peak shift was not found. The SiN x /Si 3 N 4 superlattices showed photoluminescence peak positions in the range of 540–660 nm (2.3–1.9 eV), thus quite similar to the bulk Si 3 N 4 film having peak position at 577 nm (2.15 eV). These rather weak shifts and scattering around the position observed for stoichiometric Si 3 N 4 are not in agreement with quantum confinement theory. Therefore theoretical calculations coupled with the experimental results of different barrier thicknesses were performed. As a result the commonly observed photoluminescence red shift, which was previously often attributed to quantum-confinement effect for silicon nanocrystals, was well described by the interference effect of Si 3 N 4 surrounding matrix luminescence. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4830026]