Introduction
Quantum dots are tiny particles or nanocrystals of semiconductor material with diameters in the range of 2-10 nanometers (10-50 atoms). Their optical and electronic properties differ from those of larger particles. A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons, valence band holes, or excitons in all three spatial directions. Many types of quantum dot will emit light of specific frequencies if electricity or light is applied to them, and these frequencies can be precisely tuned by changing the dots' size, shape and material.
Quantum dots exhibit properties that are intermediate between those of bulk semiconductors and discrete molecules. Larger Quantum dots (radius of 5–6 nm) emit longer wavelengths resulting in emission colors such as orange or red. Smaller quantum dots (radius of 2–3 nm) emit shorter wavelengths resulting in colors like blue and green, although the specific colors and sizes vary depending on the exact composition of the quantum dots. Their highly tunable properties give rise to many applications.
Fig 1 Quantum dots emit different wavelengths resulting in various colors.
Applications
Medical Imaging and Disease Detection: Quantum dots can be set to any arbitrary emission spectra to allow labeling and observation of detailed biological processes. Additionally, they can be utilized as a useful tool for monitoring cancerous cells and providing a means to better understand their evolution.
Solar Cells and Photovoltaic Devices: Due to quantum dots have the ability to preferentially absorb and emit radiation, they can generate optimal electric current and voltage. Utilizing quantum dots allows realization of third-generation solar cells at about 60% efficiency in electricity production.
Photocatalysts: Quantum dots can be applied as photocatalysts for the light driven chemical conversion of water into hydrogen as a pathway to solar fuel. In photocatalysis, electron hole pairs formed in the dot under band gap excitation drive redox reactions in the surrounding liquid.
Photodetector Devices: Solution-processed quantum dots can be readily integrated with an almost infinite variety of substrates, therefore they have potential applications in surveillance, machine vision, industrial inspection, spectroscopy, and fluorescent biomedical imaging.
Quantum Dot Displays: Quantum dots are valued for displays, because they emit light in very specific gaussian distributions. This can result in a display with visibly more accurate colors (Fig 2).
Fig 2 Quantum dots technology have been applied in displays.
