Dielectric matrix-driven nonlinear optical response in cylindrical core–shell quantum dots: A theoretical insight

Using the effective mass approximation and density matrix formalism, we develop a numerical model that incorporates self-polarization and bandgap discontinuity at the CdSe/ZnS cylindrical core-shell quantum dot/oxide interface. We quantitatively analyze the effects of core-to-shell radius ratio, quantum dot height and oxide permittivity on transition energies, electronic wavefunctions, oscillator strength, dipole matrix elements, and third-harmonic generation (THG) spectra. Our results reveal that surrounding oxide layers introduce additional confinement, modifying the electron energy spectrum. For a fixed shell radius R_S = 4.0 nm, the oscillator strength decreases, exhibiting a minimum near core radii R_C = 2.0 nm and 2.3 nm for HfO₂ and SiO₂, respectively. Under constant geometric conditions, the dipole matrix elements exhibit a pronounced increase with higher surrounding dielectric permittivity. In a dielectrically inhomogeneous environments, oxidation with HfO₂ (SiO₂) induces red (blue) shifts in resonance frequencies, coupled with stronger (weaker) amplitude modulation of THG peaks. These findings underscore the critical role of spatial confinement and dielectric effects in shaping the optical response of coated or solvent-dispersed nanostructures.