Based on the quantum confinement-luminescence center model, to ensembles of
spherical silicon nanocrystals (nc-Si) containing two kinds of luminescenc
e centers (LCs) in the SiOinfinity layers surrounding the nc-Si, the relati
onship between the photoluminescence (PL) and the thickness of the SiOinfin
ity layer is studied with the excitation energy flux density as a parameter
. When there is no SiOinfinity layer surrounding the nc-Si, the electron-he
avy hole pair can only recombine inside the nc-Si, then the PL blueshift wi
th reducing particle sizes roughly accords with the rule predicted by the q
uantum confinement model of Canham. When there presences a SiOinfinity laye
r, some of the carriers may tunnel into it and recombine outside the nc-Si
at the LCs to emit visible light. The thicker the SiOinfinity layer is, the
higher the radiative recombination rate occurred outside the nc-Si will be
. When the central scale of the nc-Si is much smaller than the critical sca
le, the radiative recombination rate outside the nc-Si dominates, and visib
le PL will be possible for some nc-Si samples with big average radius, grea
ter than 4 nm, for example. When there is only one kind of LC in, the SiOin
finity layer, the PL peak position does not shift with reducing particle si
zes. All these conclusions are in accord with the experimental results. Whe
n there are two or more kinds of LCs in the SiOinfinity layer, the PL peak
position energy and intensity swing with reducing particle sizes.