Probing Surface Defects Of Inp Quantum Dots Using Phosphorus K Alpha And K Beta X-Ray Emission Spectroscopy

Synthetic efforts to prepare indium phosphide (InP) quantum dots (QDs) have historically generated emissive materials with lower than unity quantum yields. This property has been attributed to structural and electronic defects associated with the InP core as well as the chemistry of the shell materials used to overcoat and passivate the InP surface. Consequently, the uniformity of the core-shell interface plays a critical role. Using X-ray emission spectroscopy (XES) performed with a recently developed benchtop spectrometer, we studied the evolution of oxidized phosphorus species arising across a series of common, but chemically distinct, synthetic methods for InP QD particle growth and subsequent ZnE (E = S or Se) shell deposition. XES afforded us the ability to measure the speciation of phosphorus reliably, quantitatively, and more efficiently (with respect to both the quantity of material required and the speed of the measurement) than with traditional techniques, i.e., X-ray photoelectron spectroscopy and magic angle spinning solid state nuclear magnetic resonance spectroscopy. Our findings indicate that even with deliberate care to prevent phosphorus oxidation during InP core synthesis, typical shelling approaches unintentionally introduce oxidative defects at the core-shell interface, limiting the attainable photoluminescence quantum yields.