Quantum dots (QDs) are semiconductor nanocrystals whose optical and electronic properties are special, as they measure a very small size, typically between 2 and 10 nanometers. These are due to quantum confinement, when the material's size approaches the exciton Bohr radius, discrete electronic energy levels appear. Quantum dots are sometimes called "artificial atoms" because they can be modified by manipulating their size, shape or structure. These nanostructures have size-dependent fluorescence, tunable emission spectra and enhanced charge transport which is ideal for applications in medicine, electronics and optoelectronics.
A quantum dot's core, shell and sometimes surface coating are normally a kind of construction. The core is generally a semiconductor layer of cadmium selenide (CdSe), indium phosphide (InP), or lead sulfide (PbS), which controls the quantum dot's key optical and electrical properties. The shell is usually made of a different semiconductor such as zinc sulfide (ZnS) to passivate the core, stopping non-radiative electron and hole recombination. This leads to a more efficient and stable fluorescence.
Quantum dots can also be tailored by tethering to their surface other ligands or molecules, such as organic or polymer compounds, to modulate solubility, biocompatibility and crosslinking with other materials. The interaction of these structural elements makes quantum dots highly tunable and can be applied to almost any type of task.
Fig.1 Structure of a quantum dot. (Rizvi, Sarwat B., et al., 2010)
We need to define quantum dots for both their physics and their uniform production and use. It's done by using different methods to describe quantum dots on a size, shape, optical and surface level.
Transmission Electron Microscopy (TEM): TEM reveals the size, shape and morphology of quantum dots in very fine detail. It allows researchers to look at quantum dots one by one and estimate their dimensionality.
X-ray Diffraction (XRD): XRD tells you about the crystallinity and phase configuration of the quantum dots. The crystal lattice and the quantum dot size are known through diffraction.
UV-Vis Absorption Spectroscopy: This is used to analyze the absorption spectrum of quantum dots, and the wavelength. It tells us how energy and band gap the substance has.
Fluorescence Spectroscopy: Quantum dots have size-dependent fluorescence, which can be measured with fluorescence spectroscopy. They can alter the excitation wavelength to get the emission spectra of quantum dots.
DLS: The quantum dots in suspension are sized using DLS. This is used to measure the uniformity and distribution of the nanoparticles in solution.
These measurements are important for evaluating the quantum dots' quality and making sure they can be used for a specific purpose.
Quantum dots can be classified based on several criteria, including their composition, shape, and surface modification. The most common classification includes:
III-V Quantum Dots: These are made from compounds of Group III and Group V elements, such as InP, GaAs, or AlAs.
II-VI Quantum Dots: Composed of elements from Group II and Group VI, such as CdSe, CdTe, and ZnS.
IV-VI Quantum Dots: Composed of Group IV and Group VI elements like PbS or SnSe.
Perovskite Quantum Dots: A newer class of quantum dots based on lead halide perovskites, such as CH3NH3PbX3, which offer excellent photophysical properties.
Spherical Quantum Dots: The most common and simplest shape, offering relatively uniform optical properties.
Rod-Shaped Quantum Dots (Nanorods): These have an elongated shape that can offer different optical behaviors from spherical quantum dots.
Dot-in-Rod Quantum Dots: These are hybrid structures that contain a small quantum dot core within a larger rod-shaped particle.
Bare Quantum Dots: These are quantum dots without any surface treatment or ligands.
Functionalized Quantum Dots: These have surface modifications with functional groups, such as carboxyl, amino, or thiol groups, which can impart specific chemical or biological properties.
The synthesis of quantum dots involves several methods, which allow control over their size, shape, and surface properties. The two most commonly used synthesis techniques are:
Colloidal Synthesis: In colloidal synthesis, quantum dots are prepared in solution by mixing precursor materials and applying heat. This method allows for precise control over the size and composition of quantum dots. The process involves a nucleation phase where small seeds form, followed by a growth phase where the particles increase in size. The size of the quantum dots can be controlled by adjusting reaction conditions such as temperature, precursor concentration, and reaction time.
Chemical Vapor Deposition (CVD): CVD is a gas-phase technique that allows for the deposition of quantum dots onto a substrate. In this method, gaseous precursors react at high temperatures to form solid quantum dots, which are then deposited onto the substrate. CVD is often used for large-scale production of quantum dots and for applications that require high-quality films or coatings.
Hydrothermal and Solvothermal Methods: These methods involve the synthesis of quantum dots in aqueous or non-aqueous solvents at high pressures and temperatures. They are particularly useful for the synthesis of quantum dots made from materials like lead sulfide (PbS) or cadmium selenide (CdSe).
Electrochemical Synthesis: Electrochemical techniques, such as electrochemical deposition, allow for the controlled growth of quantum dots on electrodes. This method is often used for the preparation of quantum dots in specific geometries for use in optoelectronic devices.
Quantum dot technology refers to the application of quantum dots in various fields, primarily in electronics, optoelectronics, and biomedical sciences. The ability to manipulate the size and surface properties of quantum dots enables the development of devices with enhanced functionality and performance. Quantum dot technology is used to improve the efficiency of solar cells, create advanced lighting solutions, and develop targeted drug delivery systems, among other applications.
The core of quantum dot technology lies in their tunable optical properties, which can be adjusted by varying the size and composition of the quantum dots. This enables the development of highly efficient light-emitting diodes (LEDs), lasers, and solar cells, as well as sensors and imaging agents for medical diagnostics.
Quantum dots work based on the principle of quantum confinement, where the electronic energy levels of the material become discrete due to its small size. When light or an electric field is applied to a quantum dot, electrons are excited to higher energy levels. When these excited electrons return to their ground state, they release energy in the form of light (fluorescence). The wavelength (color) of the emitted light depends on the size of the quantum dot. smaller dots emit light at shorter wavelengths (bluer colors), while larger dots emit light at longer wavelengths (redder colors).
This tunability of the optical properties of quantum dots is one of the key features that makes them so versatile for a variety of applications, from bioimaging to displays.
CdSe Quantum Dots: One of the most commonly used types of quantum dots, particularly for optical applications. CdSe quantum dots are often used in LEDs, solar cells, and biological imaging due to their bright fluorescence.
PbS Quantum Dots: These are used for applications in near-infrared (NIR) optoelectronics, as they emit light in the NIR range, making them useful for certain medical imaging and sensing technologies.
Perovskite Quantum Dots: These are a newer class of quantum dots that offer exceptional fluorescence properties and are used in applications like efficient solar cells, LEDs, and photodetectors.
Quantum dots have a broad range of applications across different fields, including:
Biological Imaging: Quantum dots are widely used as fluorescent probes for cellular and molecular imaging. Their tunable emission spectra allow for multi-color imaging, while their small size enables them to penetrate cells and tissues for targeted imaging.
Medical Diagnostics: Quantum dots are also used in biosensors for detecting diseases, such as cancer, by attaching them to specific biomolecules that can recognize disease markers. Their high sensitivity and ability to emit distinct colors make them ideal for such applications.
Displays and Lighting: Quantum dots are used in QLED (quantum dot LED) displays, which offer improved color reproduction, brightness, and energy efficiency compared to traditional displays. They are also used in lighting applications to create more vibrant and energy-efficient light sources.
Solar Cells: Quantum dots can be used to enhance the efficiency of solar cells by improving light absorption and increasing the conversion of solar energy into electricity. Quantum dot solar cells have the potential to surpass the efficiency of traditional silicon-based solar cells.
Quantum Computing: Quantum dots are being explored as potential building blocks for quantum computers due to their ability to represent quantum bits (qubits) in quantum information processing systems.
BOC Sciences offers a wide range of quantum dots products as well as customized products in different types to meet a variety of research and application needs. Below is the list of products we can provide, if you have more needs, please contact us to customize the synthesis of your quantum dots.
| Product Type | Price |
| Metal Sulfide Quantum Dots | Inquiry |
| Metal Selenide Quantum Dots | Inquiry |
| Metal Oxide Quantum Dots | Inquiry |
| Composite Quantum Dots | Inquiry |
| Doped Quantum Dots | Inquiry |
| Perovskite Quantum Dots | Inquiry |
| Carbon-based Quantum Dots | Inquiry |
| Silicon-based Quantum Dots | Inquiry |
| Magnetic Quantum Dots | Inquiry |
Quantum dots are made by colloidal synthesis, epitaxial growth, or chemical vapor deposition, producing nanoscale semiconductor crystals with tunable optical properties.
Quantum dots emit light through quantum confinement, where electron-hole recombination releases energy as photons, with emission color dependent on particle size.
Quantum dots can last for weeks to years depending on their composition, coatings, and exposure to environmental factors like light and oxygen.
Carbon quantum dots are fluorescent carbon-based nanoparticles with unique optical and electronic properties, used in imaging, sensing, and photocatalysis.
Quantum dots are nanoscale semiconductor particles that exhibit size-dependent optical and electronic properties, revolutionizing displays, imaging, and photonics.
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