Si/SiO2 multilayers were fabricated by RF plasma enhanced chemical vapor deposition system, and phosphorus/boron (P/B) co-doped silicon nanocrystals (Si NCs) were obtained under the constricted crystallization of multilayers structures. Microstructures of P/B co-doped Si NCs/SiO2 multilayers and impurities distributions were studied by Raman, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Low temperature electron paramagnetic resonance (EPR) results indicate that the non-radiative defects on Si NCs surfaces can be passivated by P and B impurities. Hall effect manifests that P and B impurities can substitutionally incorporate into Si NCs inner. Meanwhile, P impurity exhibits higher doping efficiency than B. Near-infrared photoluminescence near 1 200 nm with the wavelength compatible for optical telecommunication was detected in the small-sized P/B co-doped Si NCs. The emission intensity can be enhanced by regulating the nominal P-doping concentration. According to the time-resolved photoluminescence and EPR results, the physical mechanisms of P-doping on the radiative and non-radiative recombination processes of Si NCs were discussed, which are responsible for the enhancement of 1 200 nm photoluminescence.