Surface/interface engineering of colloidal quantum dots

 Colloidal quantum dots (QDs) based on II-VI (e.g., CdSe, ZnSe) or III-V (e.g., InP) compound semiconductors are useful low-dimensional building blocks for light-emitting diodes and displays because of their high PLQY approaching unity, high color purity (i.e., narrow emission spectra), and continuously-tunable emission colors controlled by the QD size, composition, and structure. Furthermore, the durability of QDs combined with their solution processability enabled rapid growths of commercial QD displays as well as their use in optoelectronics and sensors.

  Despite the numerous advantages, CdSe-based QDs cannot be used in industry because the RoHS directive restricts the use of toxic cadmium in electronics. Therefore, it is essential to develop environmentally benign QDs while maintaining the excellent optical properties of CdSe QDs.

 Colloidal QDs typically have a core/shell structure and surface ligands to increase the luminescence efficiency and maintain the material/colloidal stability. Our group focuses on the development of environmentally benign core/shell QDs where the composition, size, shape, shell structure, and surface ligands of QDs are tailored for LED applications.

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Research highlight:

[1] H. Cho et al., Advanced Materials 2020, 32(46), 2003805 

Magic-sized clusters

 Magic-sized clusters (MSCs) are zero-dimensional metastable inorganic semiconductor nanocrystals of which the size is smaller (typically < 2 nm) than the size of QDs (typically 2-10 nm). Since the energy states of MSCs are located at thermodynamic local minima, MSC tends to have high monodispersity with a specific morphology and concomitant homogeneous optical properties.

 Based on these unique properties, in-depth investigation on MSCs can provide better understanding of the nucleation and growth reactions beyond classical nucleation theory and thereby greatly contribute to the development of atomically precise synthesis of colloidal nanocrystals.

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

 1) Precise control of the morphology of II-VI and III-V nanocrystals.

 2) Atomically monodisperse colloidal nanocrystals (i.e., beyond narrow size distribution), which could even lead to optical coherence (for quantum computing)

 3) Other interesting ideas within the group!

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