LAUSR

We employed finite-difference time-domain simulations to investigate the effects of shell thickness (t), core size (r), interparticle spacing (g), and the refractive index of the surrounding medium on plasmonic coupling in Pd-TiO2 core–shell dimers, which remain understudied despite their promising optical properties. A simplified coupling model explains the spectral response through in-phase and out-of-phase interactions between plasmonic modes. The plasmon fractional shift decays exponentially with g/r, with decay constants of 2 and 4.1 for coated and bare Pd cores, respectively. While bare dimers exhibit stronger coupling at short distances, their interaction range is more limited compared to that of coated dimers. For g/r ⩽ 0.6, coupling is significant; beyond this point, both systems behave as non-interacting. Similarly, the nearfield enhancement factor follows an exponential decay, with decay constants of 10 and 16 for coated and bare Pd cores, respectively. The TiO2 shell reduces nearfield strength but helps sustain coupling over longer distances. However, increasing shell thickness lowers environmental sensitivity, as the metallic core senses the medium only indirectly through the TiO2 shell. These findings address longstanding challenges in understanding and optimizing plasmon hybridization and nearfield enhancement in complex coated nanoparticle assemblies. Overall, the results provide quantitative guidelines for tuning plasmon resonance across the UV–visible range for applications in sensing, photocatalysis, and photovoltaics.