Tunability Limit of Photoluminescence in Colloidal Silicon Nanocrystals

Abstract

Luminescent silicon nanocrystals (Si NCs) have attracted tremendous research interest. Their size dependent photoluminescence (PL) shows great promise in various optoelectronic and biomedical applications and devices. However, it remains unclear why the exciton emission is limited to energy below 2.1 eV, no matter how small the nanocrystal is. Here we interpret a nanosecond transient yellow emission band at 590 nm (2.1 eV) as a critical limit of the wavelength tunability in colloidal silicon nanocrystals. In the "large size" regime (d > ∼3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size. In the "small size" regi..