Stark effects of the fluorescence spectra in InP core and InP/ZnSe core/shell quantum dots under an external electric field.

Investigating the optical response of quantum dots subjected to an external electric field offers key insights into their suitability for nanoelectronic device integration. In this study, we employ first-principles calculations to elucidate the Stark effect in both InP core and InP/ZnSe core/shell quantum dots. Our analysis reveals three characteristic Stark shift behaviors, including quadratic, linear, and hybrid quadratic-linear responses, where each is directly linked to the evolution of the excitonic dipole moment, reflecting the intrinsic electron-hole separation (D 0i , where i = x, y, z) in the absence of an applied field. Calculated electron densities for excited states demonstrate that spectral energy ΔE increases as |D i | decreases under an external electric field, reaching a maximum when |D i | approaches zero. For all the QDs examined, D 0x is approximately zero, so an applied field along the x-direction consistently enlarges |D x |, resulting in a red shift. In contrast, the spectral response along the y or z axes depends on the alignment of the field orientation relative to D 0i : fields aligning with the electron-hole vector enhance separation (red shift), while opposing fields reduce it (blue shift). The magnitude of |D 0i | is primarily determined by core/shell electronic structure: small-core (InP)10(ZnSe)67 exhibits quasi-type II behavior with large |D 0z |, while larger-core (InP)27(ZnSe)50 and pure (InP)77 show type-I-like localization with small |D 0i |. These findings indicate that the Stark shift characteristics of InP/ZnSe QDs can be tailored by adjusting the thickness of the core or shell layer of QDs.