What is Quantum dots: Definition and 37 Discussions

Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from larger particles due to quantum mechanics. They are a central topic in nanotechnology. When the quantum dots are illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy. In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conductance band. The excited electron can drop back into the valence band releasing its energy by the emission of light. This light emission (photoluminescence) is illustrated in the figure on the right. The color of that light depends on the energy difference between the conductance band and the valence band.
In the language of materials science, nanoscale semiconductor materials tightly confine either electrons or electron holes. Quantum dots are sometimes referred to as artificial atoms, emphasizing their singularity, having bound, discrete electronic states, like naturally occurring atoms or molecules. It was shown that the electronic wave functions in quantum dots resemble the ones in real atoms. By coupling two or more such quantum dots an artificial molecule can be made, exhibiting hybridization even at room temperature.Quantum dots have properties intermediate between bulk semiconductors and discrete atoms or molecules. Their optoelectronic properties change as a function of both size and shape. Larger QDs of 5–6 nm diameter emit longer wavelengths, with colors such as orange or red. Smaller QDs (2–3 nm) emit shorter wavelengths, yielding colors like blue and green. However, the specific colors vary depending on the exact composition of the QD.
Potential applications of quantum dots include single-electron transistors, solar cells, LEDs, lasers, single-photon sources, second-harmonic generation, quantum computing, cell biology research, microscopy, and medical imaging. Their small size allows for some QDs to be suspended in solution, which may lead to use in inkjet printing and spin-coating. They have been used in Langmuir-Blodgett thin-films. These processing techniques result in less expensive and less time-consuming methods of semiconductor fabrication.

View More On Wikipedia.org
  1. J

    I Dimensions of quantum cell automata's state space

    In the paper C. S. Lent and P. D. Tougaw, "A device architecture for computing with quantum dots," in Proceedings of the IEEE, vol. 85, no. 4, pp. 541-557, April 1997, doi: 10.1109/5.573 about quantum dots, it is stated that the basis vectors in the space of quantum states for a single cell...
  2. A

    A Green's function for tunneling electrons between quantum dots

    Good afternoon! I am writing with such a problem, I hope to find someone who could help me. I'm almost desperate! So, there is such a thing as the Braess paradox, this is a classic paradox for roads and power grids, and there is also such an article...
  3. A

    Quantum Theory Of Semiconductor Quantum Dots + other books on this topic

    Hello, I have two questions into one. First I would like to know what books are considered the best to introduce the theory of quantum dots, so for example with the k.p method, tight-binding, empirical pseudopotentials, and other techniques, analytical derivations, optical properties, band...
  4. C

    Re: The electrical excitation of quantum dots

    We most often witness the presentation of quantum dots in viles or containers which are excited via UV light. I am more interested in their electrical excitation. Could I simply take a sample of QDs from one of those viles and passing an electrical current through that sample excite the...
  5. L

    Transition energy in quantum dots

    1. Homework Statement show that tthe transition energy can depend on the number of molecules in the quantum dot according to: E∝1/N^2/3 in a intro course to nanotechnology class the prof gave us this question and said that "its very easy" but i wasnt able to prove this. can someone give me...
  6. V

    A Light polarization in charged exciton in Voigt configuration

    Dear all, I'm studying a charged exciton system, composed by two ground states (electron spin up 1/2 and down state -1/2) and the two heavy hole trion state (up 3/2 and down -3/2). In this case the light which couples two ground states and the trion state has right/left polarization, to...
  7. A

    I Fluorescence from core shell quantum dots

    What is the reason for enhancement in the intensity of emission due to the introduction of a shell in quantum dots? I do understand the blue shift in quantum dots but how does a shell enhance it?
  8. U

    I Question: Quantum Dot Laser - Energy Band

    Hello I am new here, so it's nice to meet you. I study quantum dot lasers and there is something I don't understand about the energy band diagram. Quantum dots are formed with the Stranski- Krastanov method. For example small InGaAs islands of quantum dots are created on a substrate of InGaAs...
  9. bluejay27

    A Why must colloidal quantum dots be semiconductors?

    Couldn't there be conductor quantum dots or insulator quantum dots? Conductors and insulators still have energy bands.
  10. bluejay27

    I Pure semiconductor Quantum Dots?

    Can you create pure semiconductor quantum dots? I have seen composite ones that are created with elements in the group II-VI and III-V. Moreover, it saids that the size of the quantum dots must smaller than the Bohr Excitron Radius. From my understanding of the Bohr Exciton Radius is the...
  11. bluejay27

    B Do quantum dots always have to be semiconductors?

    Are there insulator quantum dots or conductor quantum dots?
  12. bluejay27

    B Can Visible Light Excite Quantum Dots to Emit Fluorescence?

    Quantum dots fluorescence whenever UV light is applied to them. Whenever the UV light is off and visible light hits the quantum dots it posses colors but does not fluorescence. I thought light had to have energy that is equal or greater than the band gap for the quantum dots to emit light. How...
  13. bluejay27

    I Are Quantum Dots Spherical? Identifying Size of Colloidal Solution

    If you were given a colloidal solution of quantum dots, how do you know that they are spherical in size?
  14. bluejay27

    I How Do Quantum Dots Emit UV Light?

    If quantum dots are placed within the body, what is the excitation needed for us to observe its emission? X-rays? I have heard that Quantum dots are used in solar cells. How does the process work for the conversion of light to electricity? I also heard that Quantum dots can emit ultra violet...
  15. bluejay27

    I Why CdS/CdSe are more widely used as quantum dots?

    Compared to other semiconductor materials, why is CdS/CdSe being more widely used as quantum dots?
  16. I

    A Shot Noise in Double-Quantum dots

    Hello all, So I am working on a problem where I need to characterize the shot noise in double quantum dots. My professor suggested to me that we can estimate the tunnel times from shot noise calculations. Can anyone give me any insight into this? Moreover, can anyone provide me any numerical...
  17. S

    A Probability of photon emission from quantum dot

    Hi guys, I am looking for a formula which I am sure exits but I cannot locate it. The problem is that a quantum dot absorbs a photon of wavelength λ0(dot is semiconductor or could be any other material). Assuming that it reemits a photon, what is the probability that this emitted photon will...
  18. E

    A Methods for finding properties of quantum dots?

    What are some good methods to determine properties such as light quality/intensity, pH, and water solubility of quantum dots? Other properties are welcome, as well. I do not have a college lab available, so some equipment may not be possible to get. This is for my science fair project next year...
  19. R

    How Do Quantum Numbers Relate to Electron Count in Quantum Dots?

    Say we have a Quantum Dot with $$n=10^{26}m^{-3}$$ and radius $$R = 3nm$$ then this will give us of the order of 13 electrons. My question is how do you relate the number of electrons to the quantum numbers n and l in order to use the spherical Bessel function values? In class for 13 electrons...
  20. Z

    Single photon, timing jitter, reduced indistinguishability?

    I saw in a recent review paper- Engineered quantum dot single-photon sources (Rep. Prog. Phys. 75 (2012))- a discussion about how a "timing jitter" problem lead to reduced indistinguishability of single photons, which I find very hard to understand. According to the paper, for quantum-dot-based...
  21. S

    Quantum Dots and the "Particle in a 1-D Box" Model

    Homework Statement The "particle in a box" is the simplest quantum system. Despite this, it still reveals a lot of important new quantum features. Please use the "particle in a 1-D box" model to explain the reason why when the size of a quantum dot gets smaller, the wavelength of the emitted...
  22. vtahmoorian

    How Do Quantum Dots Differ from Quantum Wells in Quantum Optical Properties?

    Hi everyone I am doing some researches on Quantum Dots and Quantum Wells, especially on their quantum optical properties such as nonlinear effects( refractive index, absorption) and also their interactions with deriving classical/ non classical fields and cavities .. but whenever it comes to...
  23. T

    Quantum dots Need help in analysis

    Quantum dots! Need help in analysis! :D hey guys, so long story short is that I've created gold quantum dots for my uni dissertation. These particles are formed with a protein mesh and been made to not to react with any elements as it's meant to be for human use. These gold quantum dots are...
  24. X

    Using Quantum Dots for Single Photon Creation in Lab Research

    Hello. I feel as though I should mention (before I say anything else) that this is my first year in grad school (first SEMESTER even). I haven't taken any modern physics lab courses (aside from an undergrad course years ago) that would help me with my research or my question. My PhD...
  25. P

    Rabi oscillations in quantum dots?

    someone can suggest some article or book, that explains the phenomenon of Rabi oscillations in a quantum dot? thanks and sorry for my english ;)
  26. Y

    Is the Molecular Weight of Quantum Dots Inclusive of Organic Ligands?

    Hi All, I use commercial quantum dot from evident tech, and from the datasheet I can know its molecular weight (Mw), my question is, is this Mw also includes the organic ligand or only consider its core? what is the normal case? thanks, Yuliar
  27. S

    Research Topics in Quantum Dots for Undergrad Summer Research?

    What Can be some Good Research Topics in Optical Applications of Quantum Dots? I'm Presently doing my B.Sc in electronics & require to Propose an Interesting Research Write-up for Summer Research(Duration~2 months). Personally I find Quantum Dots suits my Level of Understanding of Quantum...
  28. K

    Excitation energy of quantum dots

    Hi, i saw these parameter, excitation energy & distribution energy, in structure which have quantum dots with superlattice, and i didn't have any idea about it. can you give me definition or physical explanation about these parameters. Thank you.
  29. W

    Are Quantum Dot TVs the Future of Display Technology?

    A British company claims the first QD TVs will be on the market in a year. http://www.telegraph.co.uk/technology/news/8948484/Forget-3D-here-comes-the-QD-TV.html If true this is amazingly good news. (Well, for those of us who didn't just buy a 60" plasma TV its good news.) Theoretically they...
  30. T

    Understanding Quantum Dots: Exploring the Basics

    Can someone either explain Quantum dots for me or point me in a good direction? I didn't have much luck with the wiki's I've seen. I would like an intuitive grasp of: what they are, how they are made, and their basic functions.
  31. M

    Triplet states in quantum dots

    Hi there, I have a passing interaction with quantum dots and light emitting polymers as part of my research. I've been reading up on the physics of qdots and polymers recently. One thing that strikes me is that the existence of triplet states in polymers is mentioned, but not in quantum dots...
  32. G01

    Exploring Quantum Dots: Seeking Research Articles

    Hey Everyone, My research project this summer involves the study of Quantum Dots. I want to find some published papers covering aspects of quantum dots, fundamentals of the dots, etc. Does anyone have any suggested journal articles that you think would be a good start? Thanks a lot for the...
  33. D

    Request for Data- Band gap of CdSe quantum dots against size

    Would anybody be able to provide me with data concerning the band gap of colloidal CdSe quantum dots against their size?? I am currently using CdSe dots with a ZnS shell, capped with HDA. Any relevant information would be much appreciated. Many thanks, David Cunnah (studying PhD in opto...
  34. T

    Creating Quantum Dots: Alternatives to MBE & MOCVD?

    can someone tell me that is there other method to fabricate the GaN quantum dot without using MBE,MOCVD? is there a simple way to make a quantum dot? please reply me as soon as possible...thanks
  35. P

    Are Quantum Dots Unstable? - Paden Roder

    Sandia National lab reported that quantum dots absorb near UV and re-emit at the visible range. It's wavelength shifts to a longer wavelength with 60% efficiency. Does this mean quantum dots are unstable? Since they add mass to themselves. This makes them something different from what they...
  36. A

    Quantum Dots & Wells: Overview & Explanation

    Hello all, question time. Could someone please tell me about quantum dots and wells? Basics, details, maths, whatever you've got. Thanks.
  37. E

    Questions on Bio-tagging with Quantum Dots

    I am studying quantum dots and their applications. I have recently come across some papers describing how researchers have performed cellular imaging using quantum dots. Not that this is a new concept... it's been around since the early '90s... it's just that this is a new area for me. I...