Influence of Interfacial Strain on Optical Properties of PbSe/PbS Colloidal Quantum Dots

The interface in PbSe/PbS core/shell colloidal quantum dots (CQDs) is subject to strain forces due to a 3% crystallographic mismatch between the constituents. The strain profile in PbSe/PbS CQDs was simulated using the classical linear elasticity model, under the assumption of spherical-symmetric dot and isotropic materials. The derived strain profile was incorporated into a band structure calculation to evaluate the influence on the electronic band-edges of the core/shell CQDs. The electronic energy states evaluated were in close agreement with the absorption edges of various core/shell CQDs with different core diameters and shell thicknesses. Furthermore, the synthesized CQDs underwent thermal annealing at various temperatures, thereby creating the alloying interface; consequently, their absorption and photoluminescence spectra exhibited spectral red-shift compared with the untreated samples. The band gap energy red-shift was simulated by the theoretical model, including smoothing potential at the interface. Measurements of the photoluminescence decays indicated an extension of the radiative lifetime after a controlled annealing process, denoting removal of defect quenchers around the core shell interface. Thus, the study suggests practical means for mitigating interface strain to leverage the quality of core/shell structures.