PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Materials chemistry → Nano Chemistry ↓


Quantum dots


Quantum dots, often abbreviated as QDs, are nanoscale semiconductor particles that have unique optical and electronic properties due to their size, which is in the range of 2-10 nanometers. At this scale, materials exhibit a phenomenon called quantum confinement, which significantly affects their behavior and properties. Quantum dots are central to a variety of cutting-edge applications in materials chemistry, particularly in areas such as optoelectronics, biomedical imaging, and photovoltaics.

What are quantum dots?

Quantum dots are crystalline structures that are small enough to produce quantum mechanical effects. They are sometimes referred to as "artificial atoms" because of their discrete energy levels, similar to atoms. When a quantum dot is excited by ultraviolet light or an electrical charge, it recombines and emits light at a specific wavelength, which depends on the size of the dot.

The unique feature of quantum dots is their size-dependent optical properties. When the size of a quantum dot is reduced, the bandgap energy increases, causing a change in the color of the emitted light. Larger quantum dots emit longer wavelengths (such as red), while smaller dots emit shorter wavelengths (such as blue).

Quantum confinement and its effects

Quantum confinement occurs when the dimensions of a particle are so small that they affect its electronic properties, typically in materials smaller than 10 nanometers. In quantum dots, the motion of electrons is confined to a pseudo-zero-dimensional space, leading to shifts in energy levels. Quantum dots behave differently from bulk materials because of this quantum mechanical effect.

To understand quantum confinement more visually, imagine a three-dimensional box representing a particle. At nanoscale levels, when the size of the box is reduced, the motion of the electron within it becomes restricted, and quantized energy levels are established. Here is a simple representation:

,
| Electron |
,
,

This box represents the "pseudobox" for the electron within the quantum dot. The reduction in size of this box (quantum dot) forces the electron to occupy higher energy states, causing the observed change in color.

Synthesis of quantum dots

The synthesis of quantum dots involves complex processes that must maintain the uniformity of size and shape required for specific applications. Several techniques are used for their synthesis:

  • Colloidal synthesis: This method involves chemical reactions in a solution containing precursors. It is widely used because of the ability to control size, shape, and surface properties.
  • Vapor phase methods: These involve a phase change from vapor to solid, such as chemical vapor deposition (CVD).
  • Self-assembly: This method manipulates quantum dots to arrange them into structured patterns.

For example, cadmium selenide (CdSe) quantum dots are typically synthesized using colloidal synthesis. Precursors such as cadmium and selenium compounds react in high-temperature solvents to form nanoparticles. By adjusting the reaction conditions and processing time, the size of the nanoparticles, hence the emission wavelength, can be controlled.

Properties of quantum dots

Quantum dots are notable for their tunable optical properties. Many properties can be controlled:

  1. Size-dependent emission: As mentioned, changing the size of quantum dots allows for color tuning.
  2. High quantum yield: Quantum dots have high photoluminescence efficiency, making them bright under excitation.
  3. Wide absorption spectra: They can absorb a wide range of light wavelengths, which is useful in solar applications.
  4. Stability: Quantum dots generally show greater resistance to photobleaching than organic dyes.

Applications of quantum dots

Optoelectronics

Quantum dots are increasingly being used in displays and lighting. Quantum dot light-emitting diodes (QD-LEDs) and displays take advantage of their vibrant color range and energy efficiency. For example, many modern TV screens now incorporate quantum dot technology for improved color brightness.

         Blue Light
        
        
    Blue | Quantum | Green | Red
    led|dot|light light
        
              ,

In this scheme, a blue LED excites quantum dots, which then emit red and green light, producing the full color spectrum when combined.

Solar cell

The ability of quantum dots to absorb a broad light spectrum makes them a valuable component in solar cells. Quantum dot solar cells offer a flexible, lightweight alternative to conventional designs and have the potential to overcome the efficiency limitations of traditional silicon-based cells. Quantum dots can be tuned to absorb different parts of the solar spectrum, increasing overall energy capture.

Biomedical imaging

In the biomedical field, quantum dots are used as fluorescent probes for imaging and diagnostic purposes. Their ability to generate precise and bright emission profiles makes them superior to conventional organic dyes.

For example, in cancer imaging, quantum dots can be functionalized to target cancer cells, illuminating them under a specific wavelength of light, making high-contrast imaging possible even within complex biological tissues.

Challenges and future outlook

Despite their promising applications, quantum dots face challenges related to environmental and health impacts, particularly related to the use of toxic elements such as cadmium. Sustainable and less hazardous synthesis methods are being developed, focusing on heavy metal-free quantum dots.

Research to increase the efficiency and specificity of quantum dots continues to advance. The future will see increased integration into consumer electronics, more efficient solar technologies, and precise biomedical imaging applications.

Conclusion

Quantum dots represent a significant advance in the manipulation of material properties at the nanoscale. Their unique size-dependent properties open up a wide range of applications that are not only limited to technology and engineering but extend to health sciences and environmental solutions. Developing fields using quantum dots continue to push the boundaries, providing more efficient, cost-effective and innovative materials and devices.


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Quantum dots

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