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7A30.u1 - Quantum Dots

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​7A30.u1 - Quantum Dots

Title7A30.u1 - Quantum Dots

To demonstrate how quantum dots of different radii will fluoresce ​at different wavelengths when illuminated by a 405nm light source.

Assembly Instructions

​Provide the sealed and mounted quantum dot vials and the 405 nm laser pointer light source.  The produced fluorescing wavelengths are different enough for your eyes to tell the difference between them.  If desired, provide the Ocean Optics spectroscope with laptop computer if the professor requests it.​

Setup Time5
Operation Time5
Preview Time10
Operation Instructions

​Illuminate the quantum dot mixtures from below with the 405nm light source.  Each vial will fluoresce at a different wavelength, which is directly related to the radius of the quantum dots that are dissolved in the solution.  ​This demonstration is a real world example of the particle in a box problem.

Color          Peak Wavelength      Radius
Green         540 nm                         2.367454 nm
Yellow        570 nm                        2.533894 nm
Orange      600 nm                         2.718174 nm
Red             630 nm                         2.924941 nm
Demo on DimeNo
PIRA 200No
Export Instructions (if different)
HazardsLight Hazard - Ultra Violet

This demonstration is a real world example of the particle in a box problem.

The particle in a box problem provides a picture of the following features of quantum mechanics:
1. Energy quantization – only discrete energy levels are allowed
2. Zero-point energy – The lowest energy state is a non-zero value
3. Spatial nodes – The Schrodinger equation provides positions where the particle can exist and places where it cannot
Quantum dots are semiconductor particles that consist of electrons and “holes” that are confined in a 3-D space.  The electrons can move freely within the space, but cannot escape.  These quantum dots are used in computing situations because the presence of an electron is like having a 1 in binary code and the lack of the presence of an electron, a “hole”, is like having a 0 in binary code.
Fluorescence is the emission of light from a substance after that substance has absorbed energy.  When the quantum dots are illuminated with a short wavelength, higher energy light source, excitation of the quantum dots occurs.  This causes the quantum dots to re-emit and fluoresce at a longer, less energetic wavelength.  The physical size of the quantum dots limits what wavelength the quantum dots will fluoresce, which allows all of the quantum dots to be illuminated with the same higher energy light source and has them fluoresce at different wavelengths.
Using Schrodinger’s equation, quantum dots can be used to explain the particle-in-a-box problem.
Category7 Modern Physics
Subcategory7A - Quantum Effects
Keywordsquantum, dots, fluorescence, radii, particle-in-a-box, semiconductor, energy quantization, wave-particle duality
Construction Information
quantum dot solutions in vials - 4
laser - 405 nm 10-mW near UV
(optional) - Ocean Optics Spectrometer with Laptop Computer
laser - red 5-mW diode push button