Toroidal plasmonic nanodimers for enhanced near-infrared emission in heterostructured InP quantum dots

Near-infrared (NIR) emitters operating in the 650--900 nm spectral range are highly attractive for imaging and sensing in turbid media. However, cadmium-free InP-based quantum dots (QDs) often exhibit limited brightness owing to nonradiative recombination pathways and inefficient photon outcoupling. In particular, heterostructured InP QDs may possess band alignments that induce partial spatial separation of charge carriers, thereby reducing the electron-hole wavefunction overlap. This characteristic modifies the intrinsic recombination dynamics and increases the sensitivity of their emission to the surrounding photonic environment. Here, we investigate silver toroidal plasmonic nanoantenna dimers (Ag TPNDs) using finite-difference time-domain (FDTD) simulations as a geometry-tunable platform for enhancing the NIR emission of heterostructured InP-based QDs. The coupled toroidal geometry supports strongly confined bonding plasmon modes that generate intense electromagnetic hotspots within the nanogap, while its resonance can be systematically tuned by varying the toroid aspect ratio. By spectrally matching the antenna resonance with the QD emission bands (675--845 nm), we achieve substantial Purcell enhancement together with high quantum efficiency, demonstrating efficient conversion of the enhanced decay rates into radiative emission. Furthermore, we show that nanometer-scale variations in the emitter-antenna separation strongly influence both the radiative decay rates and the spectral response. These findings establish toroidal plasmonic nanodimers as a topology-driven platform for controlling the emission properties of NIR quantum emitters and advancing the development of NIR nanophotonic technologies.