Blue emissive quantum dots are key materials in emerging light-emitting technologies for display applications. Herein, we report the synthesis of ZnSeTe/CdZnSe-based type-II core–shell quantum dots with a low Cd content of less than 2.5%. By modifying the Cd content of the CdZnSe shell, photoluminescence emission can be tuned from 430 to 510 nm with a full width at half maximum of less than 26 nm. Transient absorption spectra illustrate the charge transfer between the conduction band of ZnSeTe and the conduction band of CdZnSe, as well as the recombination between the valence band of ZnSeTe and the conduction band of CdZnSe. By subsequent growth of ZnSe and ZnS shells, the resulting quantum dots achieved a photoluminescence quantum yield of 95%. We further demonstrate a blue quantum dot light-emitting diode with an emission peak at 467 nm, showing a maximum external quantum efficiency of 5%, a maximum luminance of 10,376 cd·m⁻², and an extrapolated T₉₅ lifetime of 4.7 h.

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.