Mitigating non-radiative decay losses in the Purcell effect at sub-10 nm nanostructure proximities

Abstract Maximizing the Purcell effect by minimizing the gap between an emitter and plasmonic nanostructures is essential for significantly increasing the spontaneous emission rate of quantum emitters. However, the enhancement of the emission quantum yield through this approach is often compromised by substantial non-radiative losses to the plasmonic nanostructures, especially when the emitter-nanostructure gap is below 10 nm. To overcome this limitation, our study presents two strategies for mitigating non-radiative losses: (1) employing plasmonic materials with high bulk plasma frequencies and low interband-transition absorption, such as aluminum (Al), thereby creating a 'valley of low loss' within the visible spectrum; and (2) examining the non-radiative decay rates in conjunction with the phase dispersion of the plasmonic dipolar modes, leading to a strategy for off-resonance spectral alignment at longer wavelengths. The 'valley of low loss' characteristic of Al results in reduced non-radiative losses in the visible-light spectrum, allowing for the tuning of the emitter's emission to coincide directly with the plasmon resonance, thus maximizing the quantum yield enhancement. Moreover, the second strategy elucidates the mechanism behind the reduced non-radiative rates in off-resonance coupling at longer wavelengths, which arises from more coherent and phase-aligned dipole field interactions between the emitter and the nanostructure. This approach is particularly advantageous for common plasmonic metals like gold, which experience pronounced non-radiative losses at resonant frequencies. By applying these strategies, we experimentally demonstrated a remarkable fourfold enhancement in the photoluminescence intensity of an F8BT-emitting material atop an Al nanodisk array.