Young‐Shin Park

Lead-halide-based perovskites have been the subject of numerous recent studies largely motivated by their exceptional performance in solar cells. Electronic and optical properties of these materials have been commonly controlled by varying the composition (e.g., the halide component) and/or crystal structure. Use of nanostructured forms of perovskites can provide additional means for tailoring their functionalities via effects of quantum confinement and wave function engineering. Furthermore, it

Charged exciton states commonly occur both in spectroscopic studies of quantum dots (QDs) and during operation of QD-based devices. The extra charge added to the neutral exciton modifies its radiative decay rate and also opens an additional nonradiative pathway associated with an Auger process whereby the recombination energy of an exciton is transferred to the excess charge. Here we conduct single-dot spectroscopic studies of Auger recombination in thick-shell ("giant") CdSe/CdS QDs with and wi

Previous single-particle spectroscopic studies of colloidal quantum dots have indicated a significant spread in biexciton lifetimes across an ensemble of nominally identical nanocrystals. It has been speculated that in addition to dot-to-dot variation in physical dimensions, this spread is contributed to by variations in the structure of the quantum dot interface, which controls the shape of the confinement potential. Here, we directly evaluate the effect of the composition of the core-shell int

Nanocrystal quantum dots (QDs) are attractive materials for applications as laser media because of their bright, size-tunable emission and the flexibility afforded by colloidal synthesis. Nonradiative Auger recombination, however, hampers optical amplification in QDs by rapidly depleting the population of gain-active multiexciton states. In order to elucidate the role of Auger recombination in QD lasing and isolate its influence from other factors that might affect optical gain, we study two typ

Biexciton photoluminescence (PL) quantum yields (Q(2X)) of individual CdSe/CdS core-shell nanocrystal quantum dots with various shell thicknesses are derived from independent PL saturation and two-photon correlation measurements. We observe a near-unity Q(2X) for some nanocrystals with an ultrathick 19-monolayer shell. High Q(2X)'s are, however, not universal and vary widely among nominally identical nanocrystals indicating a significant dependence of Q(2X) upon subtle structural differences. In

Auger recombination is a nonradiative three-particle process wherein the electron-hole recombination energy dissipates as a kinetic energy of a third carrier. Auger decay is enhanced in quantum-dot (QD) forms of semiconductor materials compared to their bulk counterparts. Because this process is detrimental to many prospective applications of the QDs, the development of effective approaches for suppressing Auger recombination has been an important goal in the QD field. One such approach involves

Advances in nanotechnology have enabled precise design of catalytic sites for CO₂ photoreduction, pushing product selectivity to near unity. However, activity of most nanostructured photocatalysts remains underwhelming due to fast recombination of photogenerated electron-hole pairs and sluggish hole transfer. To address these issues, we construct colloidal CdS nanosheets (NSs) with the large basal planes terminated by S^2- atomic layers as intrinsic photocatalysts (CdS-S<sup

We demonstrate that photon antibunching observed for individual nanocrystal quantum dots (NQDs) can be transformed into photon bunching characterized by super-Poissonian statistics when they are coupled to metal nanostructures (MNs). This observation indicates that, while the quantum yield of a biexciton (Q(2X)) is lower than that of a single exciton (Q(1X)) in freestanding NQDs, Q(2X) becomes greater than Q(1X) in NQDs coupled to MNs. This unique phenomenon is attributed to metal-induced quench

Regenerative pulsation from whispering gallery modes excited by a continuous-wave laser beam is observed in silica microspheres that feature a diminishing thermal nonlinearity near 20 K. The regenerative pulsation arises from the competition between Kerr nonlinearity and the much reduced thermal nonlinearity, when the two nonlinearities with very different timescales are comparable in magnitude but opposite in sign.

The state-of-the-art quantum dot (QD) based light-emitting diodes (QD-LEDs) reach near-unity internal quantum efficiency thanks to organic materials used for efficient hole transportation within the devices. However, toward high-current-density LEDs, such as augmented reality, virtual reality, and head-up display, thermal vulnerability of organic components often results in device instability or breakdown. The adoption of a thermally robust inorganic hole transport layer (HTL), such as NiO, beco

Neighborhood attributes are important factors influencing mental health in adults. Consensus may be needed on how to standardize the neighborhood unit or GIS-derived measures of neighborhoods in order to explain depression or psychological distress in diverse adult populations.