...When atoms and molecules form a solid, they start to lose most of their individual identity and form a "collective behavior" with other atoms. It is as the result of this collective behavior that one obtains a metal, insulator, semiconductor, etc. Almost all of the properties of solids that we are familiar with are the results of the collective properties of the solid as a whole, not the properties of the individual atoms. The same applies to how a photon moves through a solid.
A solid has a network of ions and electrons fixed in a "lattice". Think of this as a network of balls connected to each other by springs. Because of this, they have what is known as "collective vibrational modes", often called phonons. These are quanta of lattice vibrations, similar to photons being the quanta of EM radiation. It is these vibrational modes that can absorb a photon. So when a photon encounters a solid, and it can interact with an available phonon mode (i.e. something similar to a resonance condition), this photon can be absorbed by the solid and then converted to heat (it is the energy of these vibrations or phonons that we commonly refer to as heat). The solid is then opaque to this particular photon (i.e. at that frequency). Now, unlike the atomic orbitals, the phonon spectrum can be broad and continuous over a large frequency range. That is why all materials have a "bandwidth" of transmission or absorption. The width here depends on how wide the phonon spectrum is.
Phonons are quantum mechanical particles that represent the vibrational energy of a material. They are the quanta of lattice vibrations in a crystalline solid.
Phonons work by transferring vibrational energy from one atom to another within a material. They are responsible for the transmission of heat, sound, and thermal conductivity in solids.
The number of phonons present in a material is directly related to its temperature. As the temperature increases, the number of phonons also increases.
Phonons play a crucial role in determining the thermal and mechanical properties of materials. They affect thermal conductivity, specific heat, and the speed of sound in a material.
Phonons themselves cannot be directly observed, as they are a theoretical concept. However, their effects can be observed through experiments, such as inelastic neutron scattering or Raman spectroscopy.