Plasmonic fluorescence enhancement of boron vacancy centers in h-BN with TiO2-Al nanowire hybrid cavities: a simulation study.

Negatively charged boron vacancy (VB-) centers in hexagonal boron nitride (h-BN) has attracted considerable research attention due to its potential for in situ quantum sensing. However, the inherently low quantum efficiency significantly limits the sensitivity of VB- centers, which primarily arises from the low fluorescence emission suppressed by strong non-radiative recombination channels. To address this issue, here we propose and design a novel, to the best of our knowledge, nanowire (NW)-based hybrid cavity to enhance the fluorescence emission of VB- centers through both the Purcell effect and strong optical confinement. This hybrid cavity comprises an Al NW embedded within a TiO2 matrix layer covered by a few-layer h-BN flake on top. The emissivity of the optimized hybrid cavity theoretically achieves a 33-fold improvement compared with that of a conventional plasmonic scheme. To fully understand this enhancement, we also systematically simulate and reveal multiple optical confinement mechanisms, including the intrinsic absorption of Al that naturally matches well with the photoluminescence features of VB- centers, plasmonic effects, and the Fabry-Perot (FP) resonance induced by the Z-direction waveguiding property of the NW. Our work theoretically provides a promising plasmonic scheme to address the fluorescence limitations of VB- centers and extends the practical applications of the Al NW-based plasmonic method to spin-based quantum sensing.