Solid‐State Visible‐to‐Shortwave Infrared Optical Downconverters Using Nanoscale Bulk Heterojunction Quantum Dots Ensemble

ABSTRACT This work reports a novel strategy for fabricating stable and highly efficient shortwave infrared (SWIR) light emitters by incorporating lead sulfide (PbS) quantum dots (QDs) into a cesium lead bromide (CsPbBr 3 ) nanocrystal (NC) matrix. The CsPbBr 3 matrix effectively reduces surface trap states of PbS QDs and significantly enhances their quantum yield. Due to the formation of a type‐I heterostructure between PbS and the NC matrix, efficient charge transfer occurs from the matrix to the PbS QDs, leading to a substantial enhancement in SWIR emission. Optical downconverters fabricated using PbS–CsPbBr 3 ensemble exhibit a photon conversion efficiency of approximately 21%. When integrated with commercially available InGaAs photodetectors (PDs), these SWIR downconverters markedly enhance visible‐light responsivity, achieving more than a 100 00% improvement under 395 nm excitation. The CsPbBr 3 matrix serves as an ideal matrix platform for PbS QDs with varying sizes and bandgaps, enabling broadband tunability in the SWIR region. The as‐fabricated broadband downconverters, combining different‐sized PbS CQDs in a CsPbBr 3 NC matrix, demonstrate a full width at half maximum exceeding 500 nm, indicating broad spectral coverage. Moreover, the robust operational stability of the devices facilitates prototype demonstrations of SWIR spectroscopy and secure infrared optical communication.