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:
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Precise control of the morphology of II-VI and III-V nanocrystals.
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Atomically monodisperse colloidal nanocrystals (i.e., beyond narrow size distribution), which could even lead to optical coherence (for quantum computing)
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Other interesting ideas within the group!
3. Ligand Engineering
In colloidal emissive nanocrystals, ligand chemistry plays a crucial role in synthesis, surface stabilization, surface electronic structure, and device performance. Due to their inherently high surface-to-volume ratio, the structural and photophysical behavior of nanocrystals is dictated by ligand coordination. Ligands regulate precursor solubility and reaction kinetics, determining the size and morphology of nanocrystals, while simultaneously mitigating defect states and suppressing nonradiative recombination through surface passivation, ultimately enhancing photoluminescence efficiency. Furthermore, the length, polarity, and functional groups of the ligands influence interparticle interactions, film uniformity, charge transport, and interfacial stability, which in turn affect the performance of optoelectronic devices.
In particular, the introduction of functional ligands has emerged as powerful strategies to broaden the applicability of nanocrystals. For instance, incorporating photosensitive ligands with photoactive moieties enables light-triggered localized chemical reactions that induce physical property changes in the nanocrystals, thereby allowing direct optical patterning. Consequently, ligand chemistry serves as a central axis that not only ensures the structural and electronic integrity of nanocrystals but also maximizes their optoelectronic performance while supporting long-term stability and efficiency across diverse device environments.
4. QD photocatalyst
Photocatalysts are fundamental to solar-to-chemical energy conversion, facilitating key catalytic reactions such as water splitting, carbon dioxide reduction, and methane conversion. Since the pioneering discovery of photocatalytic characteristics in TiO2, significant efforts have been devoted to exploring the structure and catalytic performance of various inorganic semiconductors, such as metal oxides, oxysulfides, and metal-organic frameworks. Among the emerging photocatalysts, colloidal quantum dots (QDs) have attracted growing attention due to their size-dependent optical and electronic properties, which enable precise bandgap modulation and efficient light harvesting ability via intrinsically high extinction coefficients. Their excellent solution processability further supports scalable, cost-effective fabrication and facile integration into both colloidal suspension systems and solid-state electronic architectures. Furthermore, QDs allow for direct surface functionalization with molecular ligands or co-catalysts, which promotes charge separation and facilitates interfacial redox reactions.
In recent study, we introduce ligand-induced band offset engineering (LBOE) as a new strategy that enables efficient charge extraction of InP/ZnSe/ZnS QDs by incorporating chalcogenidometallate ligands—specifically, molecular metal chalcogenide complexes (MCCs) such as thiostannate—onto the surface of InP/ZnSe/ZnS core/shell QDs. The MCC ligands facilitate exciton dissociation by lowering the energy barrier imposed by the ZnSe/ZnS shell through LBOE and promoting efficient charge transfer to surface catalytic sites. Ultimately, by integrating MCC-functionalized InP QDs with enzymes, we achieved a record-high total turnover number (TTN) of 173,000.
