Blue emissive quantum dots are key materials in fabricating quantum-dot light-emitting diodes for display applications. Up to date, most of the previous blue emissive quantum dots are based on quantum dots with type-I core-shell structure. In this work, we report pure-blue emissive ZnSe/Cd_xZn_1−xS/ZnS quantum dots with type-II core-shell structure, which show high photoluminescence quantum yield over 90%. The type-II structure was investigated by applying time-resolved photoluminescence and transient absorption measurements, illustrating the extended photoluminescence decay lifetime of ZnSe/Cd_xZn_1−xS quantum dots as well as the transition of bleaching peak from the valence band of ZnSe to the conduction band of CdZnS. We further fabricated ZnSe/Cd_xZn_1−xS/ZnS quantum dots based electroluminescence devices, achieving a maximum external quantum efficiency of 6.7% and a maximum luminance of 39,766 cd·m⁻².

The potential use of large-size ZnSe quantum dots as blue emitters for display applications has greatly inspired the colloidal synthesis. Herein, we report the negative effects of side reactions of large-size ZnSe quantum dots. The side reactions between oleic acid and oleylamine generated amidation products and H₂O, which led to the hydrolysis of Zn(OA)₂ to Zn(OH)₂ and the subsequent formation of zinc oxide (ZnO) and zinc bis[diphenylphosphinate] (Zn(DPPA)₂) precipitates. These side reactions resulted in the formation of a defective surface including a Se-rich surface and oxygen-related defects. Such negative effects can be overcome by adopting an etching strategy using potassium fluoride and myristic acid in combination. By overcoating a ZnS shell, blue emissive ZnSe/ZnS quantum dots with a maximum photoluminescence quantum yield of up to 91% were obtained. We further fabricated ZnSe quantum dots-based blue light-emitting diodes with an emission peak at 456 nm. The device showed a turn-on voltage of 2.7 V with a maximum external quantum efficiency of 4.2% and a maximum luminance of 1223 cd·m⁻².

We report an in-situ fabrication of halide perovskite (CH₃NH₃PbX₃, CH₃NH₃ = methylammonium, MA, X = Cl, Br, I) nanocrystals in polyvinylalcohol (PVA) nanofibers (MAPbX₃@PVA nanofibers) through electrospinning a perovskite precursor solution. With the content of the precursors increased, the resulting MAPbBr₃ nanocrystals in PVA matrix changed the shape from ellipsoidal to pearl-like, and finely into rods-like. Optimized MAPbBr₃@PVA nanofibers show strong polarized emission with the photoluminescence quantum yield of up to 72%. We reveal correlations between the shape of in-situ fabricated perovskite nanocrystals and the polarization degree of their emission by comparing experimental data from the single nanofiber measurements with theoretical calculations. Polarized emission of MAPbBr₃@PVA nanofibers can be attributed to the dielectric confinement and quantum confinement effects. Moreover, nanofibers can be efficiently aligned by using parallel positioned conductor strips with an air gap as collector. A polarization ratio of 0.42 was achieved for the films of well-aligned MAPbBr₃@PVA nanofibers with a macroscale size of 0.5 cm × 2 cm, which allows potential applications in displays, lasers, waveguides, etc.