Temperature and Strain Effects on Core Bandgap and Diameter of Bare CdSe Core and CdSe/ZnS Heterostructure Core/Shell Quantum Dots

We investigated the effect of temperature dependent interface strain on the bandgap and diameter of spherical bare CdSe core and CdSe/ZnS heterostructure core/shell quantum dots (QDs) that are synthesized by colloidal technique and characterized by UV-Vis absorption spectroscopic technique. The measured band gap is used in strain dependent two band effective mass approximation to determine the core diameter of bare CdSe core and CdSe/ZnS core/shell QDs. It is found that lattice vibration dominates the shift in bandgap of CdSe core QD. On the other hand, mismatch strain due to difference between thermal expansion coefficients and lattice constants of core and shell regions dominates the core band gap shift in CdSe/ZnS QDs, causing about 0.15-0.30 eV increase in band gap (0.35-45 nm decrease in diameter) relative to unstrained value in CdSe/ZnS QD at any temperature.