Definition of colloidal quantum dots

Photonics Dictionary

colloidal quantum dots: Colloidal quantum dots (CQDs) are nanometer-sized semiconductor particles that are dispersed in a colloidal solution. These quantum dots have unique optical and electronic properties due to their size, which is typically in the range of 2 to 10 nanometers. The key characteristics and components of colloidal quantum dots include:

Quantum confinement: The small size of the quantum dots leads to quantum confinement effects, where the motion of electrons and holes is restricted in all three spatial dimensions. This results in discrete energy levels, similar to those in atoms, and gives quantum dots their unique optical properties, such as size-tunable fluorescence.

Core-shell structure: Colloidal quantum dots often consist of a semiconductor core (e.g., CdSe, PbS, or InP) surrounded by a shell of another material (e.g., ZnS) to enhance their stability and optical properties. The core determines the primary electronic and optical characteristics, while the shell can passivate surface defects and improve quantum yield.

Surface ligands: The surface of colloidal quantum dots is typically capped with organic ligands. These ligands stabilize the quantum dots in solution, prevent agglomeration, and can be tailored to modify the solubility and compatibility with different solvents and matrices.

Optical properties: Colloidal quantum dots exhibit unique optical properties, such as size-dependent emission wavelengths, high brightness, and photostability. By changing the size of the quantum dots, their emission color can be tuned across a wide spectrum, from the visible to the infrared.

Applications:

Displays: Enhancing the color gamut and brightness of LCD and LED displays.

Solar cells: Improving the efficiency of photovoltaic devices.

Biological imaging: Serving as fluorescent labels in medical and biological imaging.

Lighting: Creating efficient and stable light-emitting devices.