Optical Properties of CdSe/CdZnS Core/Shell Nanoplatelets at High Pressure

The high pressure response of the optical properties of nanomaterials affords unique insight into their mechanical properties and their interplay with the reduced dimensionality of the material. We probe the effects of high hydrostatic pressure on the optical band gap in zincblende CdSe/CdZnS core-shell nanoplatelets with 4 and 6 monolayer thick cores by following the evolution of their photoluminescence spectra from ambient pressure up to ∼6 GPa. We observe that the band gap increases nearly linearly by ∼33 meV/GPa, significantly slower than for bulk CdSe or for colloidal CdSe quantum dots in the same size regime. Using density functional theory and theoretical modeling, we trace this behavior to hardening of the CdSe core due to strain induced by lattice mismatch between core and shell, impacting the electronic structure of the core.