Photoluminescence of Si nanosolids near the lower end of the size limit

Understanding the blue shift in the photoluminescence (PL) of the nanosolid near the lower end of the size limit (D < 5 nm) seems difficult with the currently available models. This challenges are not simply numerical convergency but importantly new physics hiding behind. We examined hereby the PL blue shift of Si nanosolids smaller than 3 nm both experimentally and theoretically, leading to a conclusion that a recent "bond order-length-strength" (bond-OLS) correlation mechanism is necessary. Agreement between predictions and observations reveals that the Si-Si surface bond contracts more significantly (by ∼20%) for the smallest Si nanosolid of which the PL blue shift corresponds directly to the rise of a single bond energy of the surface atom with much lowered coordination.