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Quantum Effects. Quantum dots are unique class of semiconductor because they are so small, ranging from 2-10 nanometers (10-50 atoms) in diameter. At these small sizes materials behave differently, giving quantum dots unprecedented tunability. Relative size of quantum dots.

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Quantum dots are unique class of semiconductor because they are so small, ranging from 2-10 nanometers (10-50 atoms) in diameter. At these small sizes materials behave differently, giving quantum dots unprecedented tunability

relative size of quantum dots
Relative size of quantum dots



Matter Waves

Particle in a Box Analogy

de Broglie wavelength


The Schrödinger Equation

The Schrödinger equation is an equation for finding a particle’s wave function (x)along the x-axis.


Particle in a box

Quantized energy levels are found by solving the Schrödinger equation.

Wave function:

Allowed Energies:

quantum dots a tunable range of energies
Quantum Dots - A tunable range of energies

Because quantum dots' electron energy levels are discrete rather than continuous, the addition or subtraction of just a few atoms to the quantum dot has the effect of altering the boundaries of the bandgap

Changing the length of the box changes the energy levels

http://www.kqed.org/quest/television/nanotechnology-takes-off (3:30)


With quantum dots, the size of the bandgap is controlled simply by adjusting the size of the dot



Absorption and Emission

J. Lee et al Adv. Materials, 12, 1102 (2000)

The figure above charts the absorption and emission with corresponding visible spectrum of light colors based upon nanocrystal (quantum dot) size.

spectral codes












Wavelength (nm)

Spectral Codes

O. Dabbousi et al, J. Phys. Chem., 101, 9463 (1997).

Additionally, the spectral codes of nanocrystals may vary depending on the type of material used. For example, ZnSe emits at the ultraviolet wavelength spectrum; CdSe and CdTe are wavelengths that are visible to the human eye; and InAs is at the infrared spectrum. This figure details the varying spectral codes of the materials which are color coded by semiconductor material listed in the legend.

how quantum dots are made
How Quantum Dots are Made

Quantum dots are manufactured in a two step reaction process in a glass flask.


This is initiated by heating a solvent to approximately 500 degrees Fahrenheit and injecting precursors such as cadmium and selenium.

They chemically decompose and recombine as pure CdSe (cadmium selenide) nanoparticles.


The size of the nanocrystals can be determined based upon varying the length of time of reaction.

how quantum dots are made1
How Quantum Dots are Made



self assembled quantum dots
Self-assembled quantum dots

Each dot is about 20 nanometers wide and 8 nanometers in height

adding shells to quantum dots
Adding Shells to Quantum Dots

capping a core quantum dot with a shell (several atomic layers of an inorganic wide band semiconductor) reduces nonradiative recombination and results in brighter emission, provided the shell is of a different semiconductor material with a wider bandgap than the core semiconductor material



Quantum Dot Applications

LEDs (light emitting diodes); solid state white light, lasers, displays, memory, cell phones, and biological markers.

Biological marker applications of quantum dots have been the earliest commercial applications of quantum dots.

In these applications, quantum dots are tagged to a variety of nanoscale agents, like DNA, to allow medical researchers to better understand molecular interactions. (The Next Big Thing is Really Small, Jack Uldrich with Deb Newberry, p. 81)


Nanoparticles of cadmium selenide (quantum dots) glow when exposed to ultraviolet light. When injected, functionalized quantum dots can target cancer tumors. The surgeon can see the glowing tumor, and use it as a guide for more accurate tumor removal.


Functionalizing a Quantum Dot

The basic parts of a quantum dot include the core, shell, and surface ligand. The shell usually enhances the emission efficiency and stability of the core quantum dot. In functional uses, such as biological applications, a chemical hook is used to target complimentary materials.


Live cell imaging with biodegradable Q dot nanocomposites

Antibody-coated QDs within biodegradable polymeric nanospheres.

Upon entering the cytosol, the polymer nanospheres undergo hydrolysis and thereby release the QD bioconjugates.


Here, the nucleus is blue, a specific protein within the nucleus is pink, mitochondria look yellow, microtubules are green, and actin filaments are red.



Quantum Dots in Photovoltaics

The quantum dots can be engineered to absorb a specific wavelength of light or to absorb a greater portion of sunlight based on the application.

quantum dot laser
Quantum Dot Laser

0-D confinement in quantum dots allows for higher efficiencies and brighter lasers because you have better control of photon energies.



Quantum Dot LED