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Photoexcitation

Photoexcitation is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Photoexcitation rather than just read about it. In short: Photoexcitation is a phenomenon in physics where an excited state of a quantum system (an atom or a molecule) is created by photon absorption. The excited state originates from the interaction between a photon and the quantum system when the energy of the photon is too low to cause photoionization.

Photoexcitation — main illustration
Photoexcitation — illustration

Key takeaways

  • Photoexcitation belongs to chemistry; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Photoexcitation to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Photoexcitation from memory before moving on to harder problems.

Reference excerpt

Photoexcitation is a phenomenon in physics where an excited state of a quantum system (an atom or a molecule) is created by photon absorption. The excited state originates from the interaction between a photon and the quantum system when the energy of the photon is too low to cause photoionization. A very simple example of this process is electron excitation. A photon's energy is directly proportional to the frequency of its associated electromagnetic wave. Thus, light with lower frequencies is associated to photons with a lower energy. In contrast, light with higher frequencies is associated to photons with a higher energy. The absorption of the photon takes place in accordance with the theory of quantum mechanics. Photoexcitation plays a role in different subjects of physics and chemistry:

Photochemistry Luminescence Photoisomerization Photoelectrochemistry Moreover, photoexcitation is exploited by many different devices, such as:

Solar cells, electronic devices that convert the energy of light directly into electricity by means of the photovoltaic effect. Optically pumped lasers, devices that emit light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Photochromic applications. Photochromism causes a transformation of two forms of a molecule by absorbing a photon. For example, the BIPS molecule(2H-l-benzopyran-2,2-indolines) can convert from trans to cis and back by absorbing a photon. The different forms are associated with different absorption bands. In a cis-form of BIPS, the transient absorption band has a value of 21050 cm−1, in contrast to the band from the trans-form, that has a value of 16950 cm−1. The results were optically visible, where the BIPS in gels turned from a colorless appearance to a brown or pink color after repeatedly being exposed to a high energy UV pump beam. High energy photons cause a transformation in the BIPS molecule making the molecule change its structure. On the nuclear scale photoexcitation includes the production of nucleon and delta baryon resonances in nuclei.

See also Electron excitation Photon Photochemistry Photoelectrochemistry Photovoltaic effect Two temperature model

References

Illustrations

Photoexcitation: An illustration of electron excitation, showing excitation by photon (left) and by particle collision (right). This is the simplest case of photoexcitation, sinca a single photon excites a single quantum particle.
An illustration of electron excitation, showing excitation by photon (left) and by particle collision (right). This is the simplest case of photoexcitation, sinca a single photon excites a single quantum particle.

Worked examples

Example 1 — a first encounter with Photoexcitation

Start with the simplest possible case. Write down what Photoexcitation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Photoexcitation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Photoexcitation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Photoexcitation

In research
Photoexcitation appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Photoexcitation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Photoexcitation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Photochemistry, Physical chemistry, Time-resolved spectroscopy, so understanding it makes those chapters shorter.
In everyday life
Look for Photoexcitation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Photoexcitation in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Photoexcitation means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Photoexcitation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Photoexcitation in simple terms?

Photoexcitation is a phenomenon in physics where an excited state of a quantum system (an atom or a molecule) is created by photon absorption. The excited state originates from the interaction between a photon and the quantum system when the energy of the photon is too low to cause photoionization.

Why does Photoexcitation matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Photoexcitation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Photoexcitation.

Tags

  • Photochemistry
  • Physical chemistry
  • Time-resolved spectroscopy

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