Emission enhancement of colloidal quantum dots confined in double disc nano-antennas with controlled opening

Plasmonic nanocavities, formed by closely spaced metal nanostructures, can generate electromagnetic hotspots with significantly enhanced electromagnetic fields. Here, we introduce a strategy to form accessible hotspot regions within plasmonic double disc nanoantennas, which we use to enhance the luminescence properties of colloidal quantum dots. The nanoantennas, formed by two gold discs separated by a silica spacer, are fabricated via colloidal lithography. A controlled wet-chemical etching step partly removes the spacer, thereby exposing the cavity gap, which enables colloidal quantum dot deposition. Finite-difference time domain (FDTD) simulations are used to study the plasmonic properties of this structure and their influence on the quantum dot emission profile. These simulations show that the gap opening leads to distinct plasmonic properties capable of enhancing the quantum yield via coupling to the excitation (633 nm) and emission (900 nm) wavelengths of the QDs. Experimentally, QDs interfaced with the exposed gap by capillary forces exhibit up to a tenfold increase in photoluminescence compared to a continuous gold film and a 3.5-fold enhancement over nanoantennas with a closed gap. These findings highlight the potential of precise structural control in plasmonic devices to enhance and control emission properties of colloidal light sources.