Dielectric response of II–VI semiconductor core–shell ensembles: Study of the lossless optical condition

•Effective dielectric function of II–VI semiconductor core–shell distributions is evaluated.•The lossless optical condition is investigated in terms of geometrical and material parameters.•Negative dielectric function optical material is obtained for particular cases.•An extended Maxwell–Garnett theory is used to evaluate the dielectric response.•Finite potential confinement is used to evaluate the exciton energy in EMA approach.

We theoretically investigate optical properties of II–VI core–shell distribution mixtures made of two type-I sized-nanoshells as a plausible negative dielectric function material. The nonlocal optical response of the semiconductor QD is described by using a resonant excitonic dielectric function, while the shell response is modeled with Demangeot formula. Achieving the zero-loss at an optical frequency ω, i.e.  , ϵeff=ϵeff′+iϵeff″ with ϵeff′<0 and ϵeff″=0, is of fundamental importance in nanophotonics. Resonant states in semiconductors provide a source for negative dielectric function provided that the dipole strength and the oscillator density are adequate to offset the background. Furthermore, the semiconductor offers the prospect of pumping, either optically or electrically, to achieve a gain mechanism that can offset the loss. We analyse optimal conditions that must be satisfied to achieve semiconductor-based negative index materials. By comparing with II–VI semiconductor quantum dots (QDs) previously reported in the literature, the inclusion of phonon and shell contributions in the ϵeff along with the finite barrier Effective Mass Approximation (EMA) approach, we found similar qualitative behaviours for the ϵeff. The lossless optical condition along with ϵeff′<0 is discussed in terms of sizes, volume fractions and embedding medium of the mixtures׳ distributions. Furthermore, we estimated optical power to maintain nanocrystals density in excited states and this value is less than that previously obtained in II–VI semiconductor QDs.