Near‐infrared (NIR) lighting plays an increasingly important role in new facial recognition technologies and eye‐tracking devices, where covert and nonvisible illumination is needed. In particular, mobile or wearable gadgets that employ these technologies require electronic lighting components with ultrathin and flexible form factors that are currently unfulfilled by conventional GaAs‐based diodes. Colloidal quantum dots (QDs) and emerging perovskite light‐emitting diodes (LEDs) may fill this gap, but generally employ restricted heavy metals such as cadmium or lead. Here, a new NIR‐emitting diode based on heavy‐metal‐free In(Zn)As–In(Zn)P–GaP–ZnS quantum dots is reported. The quantum dots are prepared with a giant shell structure, enabled by a continuous injection synthesis approach, and display intense photoluminescence at 850 nm with a high quantum efficiency of 75%. A postsynthetic ligand exchange to a shorter‐chain 1‐mercapto‐6‐hexanol (MCH) affords the QDs with processability in polar solvents as well as an enhanced charge‐transport performance in electronic devices. Using solution‐processing methods, an ITO/ZnO/PEIE/QD/Poly‐TPD/MoO3/Al electroluminescent device is fabricated and a high external quantum efficiency of 4.6% and a maximum radiance of 8.2 W sr−1 m−2 are achieved. This represents a significant leap in performance for NIR devices employing a colloidal III–V semiconductor QD system, and may find significant applications in emerging consumer electronic products.

Short‐wave infrared (SWIR) light emission is important for a diverse range of modern applications, such as eye‐safe depth sensing, light detection and ranging (LiDAR), facial recognition, eye tracking, optical communication, and health‐monitoring technologies. However, there are a very limited number of known semiconductors that can emit efficiently in the SWIR spectral range. Presently, SWIR light‐emitting diodes (LEDs) based on colloidal quantum dots (CQD) are dominated by lead chalcogenide systems, despite the presence of heavy metal and modest efficiencies. Here, a highly efficient SWIR LED based on heavy‐metal‐free indium arsenide (InAs) core–shell CQDs is presented. In the LED design, the implementation of an otherwise hole‐transporting poly(vinylcarbazole) (PVK) layer on the electron‐injecting side of the device stack leads to a surprising enhancement in device performance, giving remarkably high external quantum efficiencies (EQEs) of 13.3% at 1006 nm. Single‐carrier device and optical investigations reveal the origins of enhancement to be the electronic decoupling of the CQD layer with the electron‐injecting zinc oxide (ZnO) layer, which mitigates luminescence quenching and improves charge balance. This work marks one of the highest efficiencies reported for heavy‐metal‐free solution‐processed LEDs in the SWIR spectral region, and can find significant applications in emerging consumer electronic technologies.

Indium arsenide quantum dots, which typically emit in the near-infrared, have been utilized in various optoelectronics and biomedical applications, such as covert illumination, optical communication, and deep-tissue imaging. While theory predicts that further quantum confinement through size reduction could enable visible light emission, systems with larger optical bandgaps have not been realized. Here, we report a method of preparing highly luminescent, visible-light-emitting In(Zn)As/ZnSe/ZnS QD, using a low-temperature nanocluster synthesis approach. Each QD contains an ultraconfined In(Zn)As nanocluster and fluoresces at tunable wavelengths between 538 and 640 nm with a high photoluminescence quantum efficiency of 58%. We confirm, through DFT and spectroscopic analysis, that the strong confinement effects in the few-atom-wide In(Zn)As nanoclusters are responsible for the significant spectral shift from the nearinfrared to the visible region. These findings suggest that broader-than-expected optical tuning may now be achievable in other quantum-confined semiconductor systems, which could lead to a wider scope of functional applications in optoelectronics.

Ternary CuInS2 quantum dots (QDs) with photoluminescence that is tunable from the visible to the near‐infrared (NIR) region are promising light‐emitters for consumer electronics due to the absence of toxic elements such as Pb, Cd, or As. Despite the compelling performance of visible‐light‐emitting CuInS2 QDs, reports on NIR emission remain limited, with modest efficiencies at wavelengths beyond 900 nm. In this work, the facile synthesis of NIR‐emitting CuInS2/ZnS QDs is reported. A combination of two sulfur precursors w as used in the synthesis, comprising 1‐dodecanethiol (DDT) and hexamethyldisilathiane (HMDS). The reactive HMDS facilitates faster nucleation and leads to a higher density of emissive Cu‐deficiency sites. The resulting QDs exhibit high photoluminescence quantum efficiency (PLQE) of 65% at a long emission wavelength of 920 nm. Using these QDs, NIR light‐emitting diodes (LED) are fabricated, which attain an external quantum efficiency (EQE) of 8.2%. This efficiency is comparable to the best reported PbS and InAs QD LEDs, and the emission wavelength exceeds that of lead iodide perovskites. This work thus marks one of the first reports of efficient NIR LEDs based on environmentally benign CuInS2 QDs and may open up promising new applications in consumer electronic products.

noninvasive biomedical images are created through optical and tomographic imaging such as X-ray, positron emission tomography (PET), magnetic resonance imaging (MRI), and computed tomography (CT). [1] These modalities however, depend on the use of heavy doses of ionizing radiation and/or hazardous optical contrast agents such as radioactive 18 F in the form of flurodeoxyglucose for PET, paramagnetic 64 Gd for MRI, and iodine or barium for X-ray and CT scans. [1,2] Even with the use of such harmful radiocontrast agents or ionizing radiation, these present imaging tools are still predominantly limited by their low millimeter spatial and temporal resolution for reconstructing 3D images of biological systems. [1] On the other hand, fluorescence labeling and imaging are not subject to the adverse use of ionizing radiation or radioactive tracing agents that hinder conventional tomographic imaging tools. Furthermore, fluorescent probes afford real-time image acquisition with a vastly improved spatial resolution, all while employing medically-safe visible light, near-infrared (NIR), or infrared (IR) radiation. [3,4] Amongst the different classes of fluorescent probes such as organic molecular dyes, carbon dots, and metallic clusters, colloidal semiconductor quantum dots (QDs) have emerged as promising candidates for clinical applications beyond the laboratory setting. This is due, in part, to their superior optical qualities such as a broad-based absorption spectrum with a large absorption cross-section and high photoluminescence quantum yield (PLQY). [2,5,6] Flexible tuning of QD photoluminescence (PL) to emit from ultraviolet to IR radiation through size and compositional control also realizes the possibility of multiplex detection (through dual PL emissions) and multimodal imaging to combine more than one imaging tool such as MRI and fluorescence optical imaging. [7,8] In particular, tuning the QDs' PL emission to either of the two biological spectral windows (in the NIR from 650-900 nm, or IR from 1000-1350 nm) have facilitated bioimaging with minimal tissue scattering and autofluorescence, accompanied by a significant improvement in imaging depth and spatial resolution as compared to imaging using visible light. [9-11]