Can Light Directly Heat Materials Through Phonon Absorption?

In summary, photons with an energy greater than the band gap can cause electron excitations. Prior to decaying straight to the valence band, these electrons make their way back down to the bottom of the conduction band and release heat in the form of phonons before finally emitting a photon in their decay to the valence band (for the case of a direct gap semiconductor).
  • #1
Electric to be
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After taking a course on Solid State electronics, (and doing a bit of my own research into the matter) I've gained a little bit of knowledge in the area of band structures, and phonons/photons.

My question is as follows:

I know that photons with an energy greater than the band gap can cause electron excitations. Prior to decaying straight to the valence band, these electrons make their way back down to the bottom of the conduction band and release heat in the form of phonons before finally emitting a photon in their decay to the valence band (for the case of a direct gap semiconductor).

However, is this the only mechanism by which light heats material? I've read in certain locations on this forum and other places that frequencies smaller than the band gap of photon energy are capable of directly creating phonons by absorption by the lattice (for example photon energies in the infrared). I'm not sure if this is true or not.

However, I've also read that materials are generally transparent to light that is below their band gap. For example, glass is transparent to visible light since it's band gap exceeds the visible frequencies. However, if it's true that frequencies smaller than the band gap can still cause heating through the creation of phonons, then this light that is supposed to be in transparent is in fact absorbed?Essentially, do photons only cause heat indirectly in a solid by exciting electrons and having those electrons giving up some of their energy to photons before decaying? Or is there absorption of photons that immediately become phonons (though this seems to violate the concept of "transparency", at least for photons less than the band gap, I don't know if photons greater than band gap can create phonons in a direct manner like I mentioned)..

Thank you.
 
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Baluncore said:
Optical phonons are created from a photon directly without an electron as the middle man.
https://en.wikipedia.org/wiki/Phonon#Acoustic_and_optical_phonons

So is this just another process then? Are some phonons created from electrons lowering in energy, and others are created directly via this process? For example, are acoustic phonons generated from the electrons lowering in energy? By lowering, I mean "thermalization" of electrons in the conduction band (and also emission of phonons as necessary in indirect gap transitions).

And if this optical phonon process does occur, how does it fit into the framework of the band gap? For example, IR light is said to be transparent in Silicon since it is smaller then the band gap of silicon (ideally assuming no defects). Does IR light still produce optical phonons somehow in Silicon? But then it wouldn't seem to be transparent. Does only light with energy E > Eg produce any kind of transition (optical phonon or electronic ) ?

In addition, do phonons also directly go in the reverse and have a probability of directly producing photons? I know phonons definitely can excite electrons which can then recombination and emit photons this way.
 
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  • #4
I'm not sure if this question would have been better answered in the Condensed Matter section.
 
  • #5
I'm just bumping to hopefully get a response. Thank you.
 

Related to Can Light Directly Heat Materials Through Phonon Absorption?

What is material heating by light?

Material heating by light is a process in which materials are heated by absorbing light energy. This can happen through various mechanisms, such as the conversion of light to heat energy or the generation of excited states in the material that release heat.

How does material heating by light occur?

Material heating by light can occur through different mechanisms, depending on the properties of the material and the type of light. For example, in metals, light can be converted to heat energy through the excitation of free electrons. In semiconductors, light can be absorbed and converted to heat energy through the generation of electron-hole pairs. In both cases, the energy from light is transferred to the material, causing it to heat up.

What are the applications of material heating by light?

The applications of material heating by light are wide-ranging and include heating and welding in industrial processes, medical treatments such as laser therapy, and solar energy conversion. It also plays a crucial role in various technologies, such as photovoltaics, optoelectronics, and photonics.

What factors influence material heating by light?

Several factors can influence material heating by light, including the intensity and wavelength of the light, the properties of the material, and the environment. Additionally, the duration of exposure to light and the angle of incidence can also impact the amount of heat generated in the material.

What are the challenges in studying material heating by light?

One of the main challenges in studying material heating by light is the complexity of the process. It involves various physical and chemical phenomena, making it challenging to isolate and understand the specific mechanisms at play. Additionally, the properties of the material, such as its composition and structure, can also affect the outcome of material heating by light, making it a complex and interdisciplinary research area.

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