Low‐Threshold Amplified Spontaneous Emission in Blue Quantum Dots Enabled by Effectively Suppressing Auger Recombination

The amplified spontaneous emissions in blue quantum dots (QDs) are still constrained by their high thresholds due to the challenge in engineering alloyed core-shell interface in the QDs with a wide bandgap to suppress Auger recombination. Compared with their red and green counterparts, the larger reactivity difference between the alloyed shell precursors makes it hard to regulate the composition and structure of the shell, and the smaller potential barrier between the core and the alloyed shell in blue QDs renders charge carriers tunneling into surface defects easier. Here, we employ a Lewis soft base ligand, 1-decanethiol, to balance the mismatched reactivity between Zn and Cd precursors for crafting a thick gradient alloyed shell with gradually increased potential barrier, which can not only restrict the charge carriers tunneling but also smooth the confinement potential. As a result, the resulting blue QDs show a long Auger lifetime of 1.3 ns, and a low threshold of 6.9 mu J cm(-2) excited by a femtosecond laser, which is the record value among all reported blue-emitting nanocrystals and comparable to those of state-of-the-art red and green QDs.