Colloidal Quantum Dots(QDs)

1. Surface and Interface Engineering

Colloidal quantum dots (QDs) based on II–VI (e.g., CdSe, ZnSe) or III–V (e.g., InP, InAs, InSb) compound semiconductors serve as versatile low-dimensional building blocks for light-emitting diodes and displays. Their high PLQY, narrow emission spectra, and tunable emission colors—achieved through control over size, composition, and structure—have driven rapid advances in commercial QD technologies. In particular, their solution processability and chemical durability have enabled integration into a wide range of optoelectronic and sensing platforms.

Despite the numerous advantages, CdSe-based QDs cannot be used in industry because the RoHS directive restricts the use of toxic cadmium in electronics. As a result, indium phosphide (InP) QDs have emerged as promising cadmium-free alternatives for visible-light applications. Our research focuses on advancing synthetic protocols as well as optimizing shell structures and ligand chemistry. Through detailed studies of defect states, surface passivation, and exciton behavior, we aim to improve the photostability and device compatibility of InP QDs across diverse optoelectronic and photonic systems.

In parallel, we investigate InAs and InSb QDs as narrow-bandgap, infrared-active materials. Their bandgap tunability enables emission across the near- to mid-infrared spectrum, unlocking potential in areas such as optical communication, imaging, and sensing. However, their high surface reactivity and arsenic- or antimony-rich compositions pose significant challenges. To address these issues, our group develops targeted ligand passivation strategies and finely tuned precursor chemistries to improve colloidal and electronic stability.

2. Magic-Sized Clusters

Magic-sized clusters (MSCs) are ultrasmall, atomically precise nanostructures, typically ranging from 1 to 3 nanometers in diameter, that frequently arise as intermediates during the synthesis of conventional quantum dots (QDs). Owing to their unique structural features, MSCs exhibit exceptional thermodynamic and kinetic stability, preserving a highly ordered atomic configuration even under dynamic conditions. A defining characteristic of MSCs is their discrete, molecule-like architecture, which confers uniform chemical composition and electronic structure across the ensemble. This uniformity significantly reduces interparticle heterogeneity, thereby facilitating the systematic investigation of intrinsic nanoscale properties.

Leveraging these molecular attributes, extensive studies on MSCs have substantially advanced the current understanding of their crystallographic structure, surface chemistry, and optoelectronic behavior. As such, MSCs represent a versatile and robust model system for probing phase transformations, reaction dynamics at the nanoscale, and fundamental photophysical phenomena with high precision.

NGON lab envisions the following fascinating studies based on MSCs in the future:

Precise control of the morphology of II-VI and III-V nanocrystals.
Atomically monodisperse colloidal nanocrystals (i.e., beyond narrow size distribution), which could even lead to optical coherence (for quantum computing)
Other interesting ideas within the group!