Shortwave infrared light sources are indispensable for various applications, including advanced imaging, spectroscopy, and sensing, yet their widespread adoption is limited by the high cost of epitaxial semiconductors, such as InGaAs. Downconverters (DCs) offer a cost-effective alternative, and quantum dots (QDs) stand out due to their high photoluminescence quantum yield, size-tunable emission, and solution processability. However, QD-DCs suffer from performance degradation under high excitation power densities due to significant heat generation in the process of light absorption. Here we have developed high-power, stable, and spectrally tunable narrowband and broadband SWIR DCs (1000-1600 nm) based on Lead sulfide QDs. By mixing two different-sized QDs, we exploit Förster resonance energy transfer and photon reabsorption to realize a binary system with a high photoluminescence quantum yield of 35%. Embedding the QDs in a poly-(methyl methacrylate) host mitigates local thermal stress on the QDs, enabling standalone DCs with a high emission power density (EmPD) of 110 mW/cm2 at 1380 nm. Further optimization with a spectrally selective distributed Bragg reflector for enhanced light extraction and a sapphire substrate for efficient heat dissipation, we achieved a record EmPD of 385 mW/cm2 at 1380 nm with optical power conversion efficiency of 10% and operational stability above 230 h at an EmPD of 190 mW/cm2. This demonstrates a scalable route to low-cost SWIR light sources, narrowing the performance gap between solution-processed DCs and conventional epitaxial semiconductors.
Malla et al. (Fri,) studied this question.