Metal halide ligand-assisted purification for enhancing luminescence performance of ZnSeTe-based pure-blue quantum dots

Colloidal quantum dots (QDs) usually surfer from incomplete ligand coverage due to the steric hinderance of bulky long-chain ligands used in the synthesis stage and ligand desorption during the purification process. In this work, a metal halide ligand-assisted purification (LAP) method is developed for the first time and applied to enhance the luminescence performance of eco-friendly ZnSeTe-based pure-blue QDs synthesized without HF. Compared to the traditional purification (TP) method, the LAP approach is capable of enhancing the photoluminescence quantum efficiency (PLQY) and environmental stability of the QDs without compromising their colloidal stability and solution processability for uniform thin-film fabrication. Among the three zinc halide ligands (ZnCl 2 , ZnBr 2 , and ZnI 2 ), ZnCl 2 -assisted purification achieved the most significant photoluminescence enhancement, increasing the QDs’ PLQY from 57% (obtained through TP) to 82%. This improvement is attributed to the fact that the small-sized chloride ligands effectively passivate QD surface defects via binding to undercoordinated surface atoms during purification. The pure-blue light-emitting diode based on the optimal LAP-QDs displayed a 4-fold increase in maximum luminescence intensity and a 1.5-fold enhancement in peak external quantum efficiency compared to that based on the TP-QDs. This study demonstrates a simple yet efficient purification strategy for improving colloidal QD luminescence.