This work presents a theoretical and numerical investigation of the optical properties and slow-light behavior of CdS@ITO core–shell quantum dots (CSQDs) designed for operation in the 1310 nm and 1550 nm telecom bands. Using quasi-static electrodynamics, Maxwell–Garnett effective medium theory, and the Drude–Sommerfeld model, we demonstrate that the ITO shell supports low-loss infrared plasmonic resonances with extinction coefficients below \(\kappa < 0.06\) . Hybrid exciton–plasmon coupling between the CdS core and ITO shell produces strong local field enhancement ( \(|F|^{2}> 1000\) ) and pronounced normal dispersion, enabling slow-light behavior with group velocities as low as \(v_{g} \approx 0.05c\) . Geometric tuning of the core radius (3–5 nm) and shell thickness (6–8 nm) enables precise alignment of the plasmonic resonance with standard telecom wavelengths. Finite element simulations confirm intense field localization at the CdS/ITO interface and enhanced internal fields within the CdS core, supporting Kerr-type nonlinear effects relevant for optical modulation. Parametric mapping of extinction, refractive index, and group index further demonstrates robust spectral tunability and low-loss performance across the near-infrared region. These findings identify CdS@ITO CSQDs as promising, CMOS-compatible nanostructures for compact optical delay lines, all-optical modulators, and other integrated photonic components operating within the telecom band.
