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In solids (most any object we see), which tends to emit most of the blackbody radiation: phonons (atomic, or molecular dipole, lattice vibrations) or oscillating electrons in their energy bands?

adam3033
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    Do you have something against plasmons? – Jon Custer Feb 29 '16 at 22:21
  • Jon Custer -- Plasmons give off just ultraviolet, correct .. and only associated with metals? What about the cause of infrared blackbody from non-metallic objects? – adam3033 Mar 02 '16 at 16:27
  • Why would plasmons only give off ultraviolet? The main plasmon resonance in gold is in the blue (which is why gold is, well, gold colored). If there is an electronic structure, there are interactions between propagating EM modes and the electron structure. These go by various names, such as plasmons (usually associated with free electrons), polaritons (dipole interactions), ... – Jon Custer Mar 02 '16 at 16:32
  • But what about non-metallic objects? I've heard it said that it's the oscillations in electron density that cause blackbody. My confusion with that is, with non metals, how can there be continuous oscillations in the valance shell/orbitals giving off infrared if the band is full? And I say valance shell because for non metals obviously there isn't a conduction band with electrons. So it would have to be electrons in the valance shell giving off infrared, correct? And, again, if so, how are they oscillating if the valance band is full? – adam3033 Mar 02 '16 at 16:45
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    Contemplate a ceramic. stretching of the metal-oxygen bond will likely create a dipole moment (certainly clear in piezo materials). Such a dipole moment interacts with / causes EM fields, which may result in photon emission. – Jon Custer Mar 02 '16 at 16:48
  • Jon Custer -- Which is the greater emitter of blackbody radiation from the conduction band: oscillating free electrons or just plasmons? Do they both emit infrared? – adam3033 Mar 05 '16 at 13:12

2 Answers2

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A couple snippets from the web:

I can't find the actual document name, but it's here

Phonons are quantized lattice vibrations. They possess small energies (up to approximately 100meV) and a momentum of the order of that of an electron in a semiconductor. Which suggests that phonon energy is far too small to emit photons (other than longwave radio, perhaps).

The wikipedia article on direct vs indirect bandgap material says that phonons are only involved in emission or absorption when the photon's energy is slightly greater than that involved in an electron transition, so the photon "makes up the difference."

But keep in mind that there is no physical phonon particle: it's just a way of describing the quantized vibrational energy in a solid. You can't directly convert vibrational energy into a photon, although the energy can affect the final energy of a photon emitted in a quantum process (such as electron level shifts). There's a pretty good discussion at this Physics.SE page.

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Carl Witthoft
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  • just read about that. Thanks for the link. So a phonon-electron interaction. Would make sense. Would you see the the vibrational energy converting to electronic energy as the electron becomes excited? – adam3033 Feb 26 '16 at 14:46
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Excellent question. The excitations involved are from occupied conduction (metals) or valence states (insulators, semiconductors) to unoccupied conduction band states. These form a continuum so can emit a continuous black body spectrum. These excitations are also responsible for the dielectric response.

my2cts
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