Upper limit of blue shift in the photoluminescence of CdSe and CdS nanosolids

Adding the effect of surface bond contraction to the Hamiltonian of an extended solid leads to a new mechanism indicating that the blue-shift in the photoluminescence (PL) of CdS and CdSe nanosolids arises from the surface-relaxation-enhanced binding energy and the PL shift depends on the portion of surface atoms of the solid. Consistency between predictions and observations evidences that a surface bond contracts more than it does on a flat surface when the surface curvature increases and that the Cd-Se bond contracts faster than the Cd-S bond when the solid approaches to the lower end of size limit.