Enhanced fluorescent stability of copper indium sulfide quantum dots through incorporating aluminum into ZnS shell

Abstract

Fluorescent quantum dots (QDs) become usually deteriorated, losing their originally high quantum yield (QY), upon a prolonged exposure to degradable environments, and this lack of long-term QD stability retards their ultimate industrial application. For an effort to significantly improve the fluorescent stability of copper indium sulfide (Cu–In–S, CIS) QDs, in this work, synthesis of double-shelled CIS/ZnS/ZnS:Al QDs with intermediate ZnS shell and outer Al-doped ZnS shell is attempted. The resultant yellow-emitting CIS/ZnS/ZnS:Al QDs possess an excellent QY of 77%. For comparison, standard double shell-structured, Al-doping free CIS/ZnS/ZnS QDs are also prepared. These two types of QDs are then subjected to continuous UV irradiation and heat for certain periods of time and their temporal fluorescent stability behaviors are compared, clearly showing a superior stability from QDs with Al-doped shell. This is attributable to the effective QD passivation by Al2O3 layer generated via photochemical or thermal oxidation of Al doped in ZnS shell. The above results are further verified by fabricating QD-based light-emitting diodes (LEDs) with the combination of QD down-converters with a blue LED and comparing their electroluminescent stability with operational time.