Plasmon-enhanced near-infrared fluorescence and optical communication of PbS quantum dots with gold nanorod arrays

Lead sulfide quantum dots (PbS QDs) offer significant potential for near-infrared (NIR) free-space optical communication (FSOC) due to tunable bandgaps and broad spectral response. However, their microsecond-scale photoluminescence (PL) lifetimes and pronounced Auger recombination critically limit modulation bandwidth and signal-to-noise ratios. Plasmonic nanostructures can address these limitations via the Purcell effect, but the involved lithographic fabrication compromises scalability and precise sub-wavelength structuring. This work presents a facile, lithography-free methodology for dense, vertically aligned gold nanorod (Au NR) arrays with strong localized surface plasmon resonance (LSPR) across the NIR. By combining seed-mediated synthesis of high-aspect-ratio Au NRs (>8) with precise solvent evaporation-induced self-assembly (EISA) on functionalized substrates, vertically oriented arrays are achieved. The integration of vertical and well-aligned Au NR arrays with PbS QD photoconversion layer induces a 769% peak PL intensity enhancement at resonance. Moreover, the Purcell effect from strong near-field confinement accelerates spontaneous emission, reducing the ensemble-average PL lifetime from 860 ns to 279 ns – a critical advance for bandwidth. Within a representative FSOC link employing intensity modulation, the optimized plasmon-enhanced PbS QD photoconversion material achieves a −3 dB bandwidth of 930 kHz and supports 2.0 Mbps on–off keying (OOK) with a bit error rate (BER) of 3.8 × 10⁻ 3 under ambient conditions. This demonstrates a promising improvement over baseline QD devices and validates the efficacy of the EISA-fabricated plasmonic array for high-speed NIR FSOC.