Blue-emitting heavy-metal free QDs simultaneously exhibiting photoluminescence quantum yield close to unity and narrow emission line widths are essential for next-generation electroluminescence displays, yet their synthesis is highly challenging. Herein, we develop the synthesis of blue-emitting QDs by growing a thin shell of ZnS on ZnSe cores with their size larger than bulk Bohr diameter. The bulk-like size of ZnSe cores enables the emission to locate in the blue region with a narrow emission width close to its intrinsic peak width. The obtained bulk-like ZnSe/ZnS core/shell QDs display high quantum yield of 95% and extremely narrow emission width of ∼9.6 nm. Moreover, the bulk-like size of ZnSe cores reduces the energy level difference between QDs and adjacent layers in LEDs and improves charge transport. The LEDs fabricated with these high-quality QDs show bright pure blue emission with an external quantum efficiency of 12.2% and a relatively long operating lifetime.

Developing high-quality and cadmium-free blue quantum dots (QDs) and their corresponding efficient light-emitting diodes (LEDs) is essential for facilitating their industrialization. ZnSe-based QDs as the prospective blue alternative material for cadmium-based QDs have attracted great attention. However, realizing efficient blue-emitting, especially deep-blue-emitting, devices is seriously limited by the deep valence band and excessive defect states in the wide bandgap QDs. Although the common electron transport layer, that is, ZnO nanoparticles (NPs) can provide effective electron injection, the large hole injection barrier usually causes unbalanced charge injection. Here, we report deep-blue cadmium-free QLEDs at 443 nm with improved efficiency and operational lifetime employing ZnO with Sn doping for mitigating electron over-injection. Theoretical and experimental results reveal that Sn doping causes an upshifted ZnO conduction band and reduces its electron mobility and defect sites. Thus, the electron over-injection in devices is inhibited to achieve charge balance, and the exciton quenching in QDs is reduced to improve radiation recombination. Resultantly, the external quantum efficiency of devices is improved to 13.6 from 5.1%, and the device lifetime (T50@100 cd m–2) is enhanced 21-fold, reaching 305 h, representing the best among ZnSe-based QLEDs so far. These results offer an effective pathway for deep-blue QLEDs toward commercialization.

Indium phosphide (InP) quantum dots (QDs) are ideal substitutes for widely used cadmium‐based QDs and have great application prospects in biological fields due to their environmentally benign properties and human safety. However, the synthesis of InP core/shell QDs with biocompatibility, high quantum yield (QY), uniform particle size, and high stability is still a challenging subject. Herein, high quality (QY up to 72%) thick shell InP/GaP/ZnS core/shell QDs (12.8 ± 1.4 nm) are synthesized using multiple injections of shell precursor and extension of shell growth time, with GaP serving as the intermediate layer and 1‐octanethiol acting as the new S source. The thick shell InP/GaP/ZnS core/shell QDs still keep high QY and photostability after transfer into water. InP/GaP/ZnS core/shell QDs as fluorescence labels to establish QD‐based fluorescence‐linked immunosorbent assay (QD‐FLISA) for quantitative detection of C‐reactive protein (CRP), and a calibration curve is established between fluorescence intensity and CRP concentrations (range: 1–800 ng mL−1, correlation coefficient: R2 = 0.9992). The limit of detection is 2.9 ng mL−1, which increases twofold compared to previously reported cadmium‐free QD‐based immunoassays. Thus, InP/GaP/ZnS core/shell QDs as a great promise fluorescence labeling material, provide a new route for cadmium‐free sensitive and specific immunoassays in biomedical fields.

Low-toxic InP quantum dots (QDs) as an ideal candidate for Cd-based QDs have tremendous potential for next-generation commercial display and biological detection applications. However, the progress in biological detection is still far behind that of the Cd-based QDs. This is mainly because the InP-based QDs are of inferior stability and photoluminescence quantum yield (PL QY) in aqueous solution. Here, PL QY of 65% and excellent stability of InP/GaP/ZnS QD@SiO2 nanoparticles have been successfully synthesized via a silica coating method. The containing thiol-capped hydrophobic InP/GaP/ZnS QDs were pre-silanized with waterless, ammonia-free hydrolysis tetraethyl orthosilicate, and subsequently, an outer silica shell was generated in the reverse microemulsion. The corresponding QD-based fluorescence-linked immunosorbent assay exhibits a high sensitivity of 0.9 ng mL–1 for C-reactive protein and the broad detection range of 1–1000 ng mL–1, which was close to that of the state-of-the-art Cd-based QD@SiO2 nanoparticles and had the highest sensitivity of Cd-free QDs so far. This work provides a very successful silica coating method for the containing thiol-capped hydrophobic QDs and the QDs highly sensitive to water and oxygen, and the obtained InP/GaP/ZnS QD@SiO2 nanoparticles were considered as the robust, biocompatible, and promising Cd-free fluorescent labels for the further ultra-sensitive detection.

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