Do excited silicon-oxygen double bonds emit light?

Oxidation of the surface of well-passivated silicon nanocrystals introduces defects which dramatically affect the optical properties of the material. One such defect is the silicon-oxygen double bond, which has been implicated as the source of the unusual particle-size-independent S-band photoluminescence of oxidized silicon nanocrystals. Herein, we investigate the photodynamics of this defect by application of a first-principles nonadiabatic molecular dynamics approach to a cluster model containing a silicon-oxygen double bond. Upon excitation, pyramidalization occurs about the double-bonded silicon atom, leading to a conical intersection between the ground and first excited state. This conical intersection facilitates nonradiative decay, resulting in the internal conversion of 7% of the excited population in the first picosecond after excitation. Extrapolation to longer times suggests that nonradiative decay via conical intersection proceeds faster than the microsecond photoluminescence lifetime of silicon nanocrystals and thus that silicon-oxygen double bonds are unlikely to be responsible for the experimentally observed emission.