If I have to choose the most badass phrase from my experiment, “quantum confinement effect” is the most compelling candidate. Yes, we nanochemists can control the “quantum confinement effect” in our laboratory by our own hands. (Blah!)
Today’s topic is about semiconductor nanocrystals, as known as quantum dots. Quantum dots are another reason why nanochemistry has been one of the hottest topics in science in the past decade. The shininess of the quantum dots and variety of the colors that quantum dots emit are very useful for display. You may hear QLED displays in Target or Walmart. It is the abbreviation of “quantum-dot light-emitting diode.” The superior optoelectronic properties are a perfect fit for solar-cell materials. As of 8/17/2019 when I am writing this post, the efficiency of the state-of-art quantum-dot based solar cell reach 16.6%. The improvement of the efficiency record has never stopped. It is exciting to imagine what happens in, let’s say, 10 or 15 years.
Quantum dots used here refers to nanosized semiconductors of which size is close or less than the Bohr radius, which is a theoretical parameter unique to the material composition. For example, the Bohr radius of CdSe is 5.4nm. CdSe materials smaller than 5.4nm emerge quantum confinement effect, leading to the generation of unique molecular orbitals. There are a lot of things that I can talk about in this process, but practically speaking, this will lead to the size-dependency of fluorescence.
In the synthesis point of view, you always want to monitor
The absorption and fluorescence evolution
The quantum yield and the surface state (fluorescent quenching can happen when the surface is not good)
The core-shell synthesis and the related shape effect (like nanorods or tetrapods)
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| Very nice schematics about quantum confiniment effect. The figure is from this paper. |
Quantum dots synthesis is satisfying because when you nail it, the product is shiny and beautiful. And understanding physics behind the beautiful color gives you another satisfaction that you are really controlling the “quantum confinement effect” by our own hands.
Good luck with confining quantum effect.
