The impact of lattice strain on optical properties of CdS nanocrystals

• ZnS shell formation on CdS NCs compresses core by 3% as shell thickness increases.
• Stoke׳s shift of these NCs indicate redistribution of oscillator strength.
• The Stoke׳s shift also indicates mixing of s-type and p-type hole levels.
• Life times show sudden change with shell thickness larger than two monolayers.

CdS nanocrystals (NCs) with size 4.3 nm, were coated with ZnS to form CdS/ZnS core shell in order to examine the effect of lattice strain due to lattice mismatch of 7%. Besides structural analysis, the optical absorption spectrum red-shifts with increasing ZnS shell thickness affirming core–shell nanostructure formation. Radiative life time of CdS NCs remains invariant up to two monolayers of ZnS on CdS NCs and reduces to half the value at three monolayers onwards. The experimental finding is indicative of strain induced change in symmetry of hole wave-function in ground state.