graphene
Quantum dots usually have II-VI or III-V semiconductor layers like cadmium selenide (CdSe) and cadmium sulfide (CdS). These have band gaps that make quantum dots unusually sized in optical and electronic aspects. The quantum dots' surfaces also frequently are inked with organic or inorganic materials, which keep them chemically stable and alter their optical properties.
For better illustration of quantum dots' mechanism, think of them as tiny cages in which electrons fit into an extremely tiny cavity. If you place energy, like light or electricity, on the quantum dots, the electrons pick up the energy and rise to higher energy. When they fall back down to zero energy, they produce light of a particular wavelength. This is what makes quantum dots so powerful in luminescent and optoelectronic devices.
How Do Quantum Dots Work?
Quantum dots are semiconductor nanoparticles where the quantum confinement effect is the working principle. This action keeps electrons and holes in a nano-sized box, changing their optical and electronic properties drastically.
Quantum Confinement
Quantum confinement describes the way that electron energy states split up when a material is condensed to the scale analogous to or smaller than the de Broglie wavelength of the electron wavefunction. It occurs because the electron wavefunction is locked up within nanostructures in spatial entanglement so that the electrons can only be at particular energies. Quantum dots are like three-dimensional "boxes" with electrons and holes locked inside a finite space and creating discrete energy levels.
How Does Quantum Dot Size Affect Performance?
Relationship Between Size and Emission Color
Quantum dots are the size and emission colour of a rhodium atom. For the most part, small quantum dots glow blue, big quantum dots glow red. It's because quantum dots of different sizes have bandgap energy variations that influence the wavelength of the reflected light. If a quantum dot's size decreases, for example, the bandgap energy increases and the emission wavelength is shifted towards shorter wavelengths – from red to blue.
Importance of Dimension (2D vs. 3D)
Quantum dots have very strong optical effects depending on their size. In 2D quantum dots, for example, the bandgap energy is very sensitive to change with size and gives highly customizable emission colours. But in 3D quantum dots this alteration is much smaller because electrons and holes are more evenly distributed in 3D systems, and thus sizes change the bandgap less. Therefore, 2D quantum dots are usually chosen for applications where a specific emission wavelength is needed, like bioimaging and display technology.
Practical Examples of Size-Dependent Applications
The quantum dot's size dependence is useful in a wide range of areas. In bioimaging, for example, quantum dots of different sizes can mark several biological targets at once, making multiplex imaging possible.