Impact of Different Ligands on Nanocrystal Structural Disorder and Quantum Yield

The goal of our lab is to understand the influence of surface states and transient disorder on the photoluminescence efficiency of semiconductor nanocrystals for use in device applications. A few NC systems (e.g. CdSe:CdS and PbS) have been optimized to reach near-unity quantum yield under weak excitation, but have been shown to achieve lower quantum yield under intense excitation required for certain applications such as lasers or LEDs. We use correlative measurements to understand the role of structural disorder in increased nonradiative decay under high intensity excitation.<br/>We first quantify the power-dependent photoluminescence quantum yield of semiconductor nanocrystals (NCs) as a function of surface ligand chemistry, using a homebuilt quantum yield spectrometer, calibrated by primary standards. Nanocrystals with differing ligand passivation are measured with time-resolved photoluminescence and photoluminescence quantum yield to understand their radiative and nonradiative decay pathways. Finally, time-resolved X-ray diffraction (XRD) is used to measure the influence of differing ligands on electron-photon coupling and transient disorder in NC systems.