Synthesis of full-visible-spectrum luminescent silicon nanocrystals and the origin of the luminescence

An efficient synthesis route for highly luminescent silicon nanocrystal (Si-nc) films is presented. Si-ncs in the films are synthesized in the gas phase by using an argon-silane radio-frequency dielectric-barrier discharge (RF-DBD) plasma. The size of Si-ncs is well tunable by changing the resident time. The resulting Si-nc films with different oxidation degree exhibit emission across the full visible spectrum. Structural and optical characterization indicates that the red-to-green luminescence from big particles show quantum confinement effect (QCE), while this effect disappears in blue luminescence from small ones. A model is presented to explain this result. In this model, the radiative process in big particles is Band-to-Band recombination, in which surface states have a negligible impact on the QCE, while the blue emission from small Si-ncs is due to the Band-to-Bound recombination, in which surface state plays an important role, resulting in the disappearance of QCE. Additionally, obvious double-exponential decay from midsize particles is observed, in which the two kinds of recombination may coexist.