Cation-Exchange-Derived InGaP Alloy Quantum Dots toward Blue Emissivity

Abstract

In contrast to a substantial progress of heavy metal-free green and red emitters exclusively from indium phosphide (InP) quantum dots (QDs), the development of non-Cd blue QDs remains nearly unexplored. The synthesis of blue InP QDs with a bright, deep-blue emissivity is not likely viable, which is primarily associated with their intrinsic size limitation. To surmount this challenge, herein, the first synthesis of blue-emissive ternary InGaP QDs through In3+-to-Ga3+ cation-exchange strategy is implemented. Pregrown InP QDs turn out to be efficiently Ga-alloyed at a relatively low temperature of 280 °C in the presence of Ga iodide (GaI3), and the degree of Ga alloying is also found to be systematically adjustable by varying GaI3 amounts. Such cation-exchanged InGaP cores are surface-passivated sequentially with ZnSeS inner and ZnS outer shells. As the amount of GaI3 added for cation exchange increases, the resulting double-shelled InGaP/ZnSeS/ZnS QDs produce consistent blue shifts in photoluminescence (PL) from 475 to 465 nm, while maintaining high PL quantum yield in the range of 80–82%. Among a series of QD samples, above 465 nm emitting InGaP/ZnSeS/ZnS QDs are further employed as an emitting layer of an all-solution-processed electroluminescent device. This unprecedented InGaP QD-based blue device generates maximum values of 1038 cd/m2 in luminance and 2.5% in external quantum efficiency.