Engineering Brightness-Matched Indium Phosphide Quantum Dots

The size-dependent optoelectronic properties of semiconductor nanocrystal quantum dots (QDs) are hugely beneficial for color tunability but induce an inherent relative photoluminescence brightness mismatch in QDs emitting different colors as larger emitters absorb more incident photons than smaller particles. Here, we examine the effect of core composition, shell composition, and shell thickness on optical properties including high energy absorption, quantum yield (QY), and the relative brightness of InP/ZnS and InP/ZnSe core/shell and InP/ZnSe/ZnS core/shell/shell QDs at different excitation wavelengths. Our analysis reveals that the presence of an intermediate ZnSe shell changes the wavelength of enhanced absorption onset and leads to highly excitation wavelength-dependent QYs. Switching from commercial CdSe/ZnS to InP/ZnS reduces the brightness mismatch between green and red emitters from 33-to 5-fold. Incorporating a 4-monolayer thick optically absorbing ZnSe shell into the QD heterostructure and heating the QDs in a solution of zinc oleate and trioctylphosphine produces InP/ZnSe/ZnS QDs that are similar to 10-fold brighter than their InP/ZnS counterparts. In contrast to CdSe/CdS/ZnS core/shell/shell QDs, which only photoluminesce at red wavelengths with thicker CdS shells due to their quasi-type II band structure, type I InP/ZnSe/ZnS QDs are uniquely suited to creating a rainbow of visible-emitting, brightness-matched emitters. By tailoring the thickness of the intermediate ZnSe shell, heavy metal-free, brightnessmatched green and red emitters are produced. This study highlights the ability to overcome the inherent brightness mismatch seen in QDs through concerted materials design of heterostructured core/shell InP-based QDs.