How about the energy of crystal in a direct transition?

In summary, when a photon is absorbed by an electron in a crystal, the crystal momentum of the electron remains relatively unchanged, causing the crystal to also gain momentum. However, the energy of the crystal is not considered in this process, with only the absorbed energy being attributed to the electron's transition. In the case of a crystal with infinite mass, its momentum and energy both become 0, making it irrelevant for energy conservation.
  • #1
hokhani
483
8
When a photon is absorbed by an electron through a direct transition in a crystal, the crystal momentum of electron would not approximately change. Therefore momentum change of electron would neutralize momentum change of crystal. In other words, the crystal would gain momentum as well as electron. But why we don't consider the energy of crystal in this process (we consider all the absorbed energy only as energy of electron transition)?
 
Physics news on Phys.org
  • #2
How big is the energy change of a crystal of mass ##M \to \infty## if its momentum changes by ##\Delta P##?
 
  • #3
Suppose conduction and valence bands are parabolic with the same curvature. If we were to consider the conservation of kinetic energy before and after absorption, the photon energy must be equal to " change of electron's kinetic energy + change of crystal's kinetic energy). According to our supposition electron velocity and hence it's kinetic energy doesn't change so the change of crystal's kinetic energy is equal to the photon energy. Therefore all the photon energy is transferred into kinetic energy of crystal! Could you please help me?
 
  • #4
No, what I mean is that the crystal's momentum changes from 0 to P and its energy from 0 to ##E=P^2/2M##. If P is finite, E becomes 0 in the limit of infinite mass of the crystal.
So the crystal takes care of the conservation of true momentum, but is irrelevant for energy conservation.
 
  • Like
Likes 1 person

Related to How about the energy of crystal in a direct transition?

What is a direct transition in the context of crystal energy?

In crystal physics, a direct transition refers to the process in which a crystal changes from one energy state to another without any intermediate states. This means that the energy of the crystal changes abruptly and without any gradual changes in between.

How is the energy of a crystal affected during a direct transition?

The energy of a crystal is affected during a direct transition as the atoms in the crystal rearrange themselves into a new, more stable energy state. This rearrangement results in a change in the overall energy of the crystal.

What factors influence the energy of a crystal during a direct transition?

The energy of a crystal during a direct transition is influenced by several factors, including temperature, pressure, and the arrangement of atoms in the crystal lattice. Additionally, external forces such as electric or magnetic fields can also impact the energy of the crystal during a direct transition.

Can the energy of a crystal be controlled during a direct transition?

Yes, the energy of a crystal during a direct transition can be controlled to some extent. By manipulating the external factors that influence the energy of the crystal, such as temperature or pressure, scientists can guide the crystal to transition to a desired energy state.

What are some real-world applications of studying the energy of crystals in direct transitions?

Understanding the energy of crystals in direct transitions has several practical applications, including in the development of new materials for use in electronics, energy storage, and medical devices. It also has implications for the production of more efficient and sustainable energy sources, such as solar cells and batteries.

Similar threads

  • Atomic and Condensed Matter
Replies
1
Views
2K
  • Atomic and Condensed Matter
Replies
19
Views
2K
  • Atomic and Condensed Matter
Replies
4
Views
1K
  • Atomic and Condensed Matter
Replies
23
Views
2K
  • Atomic and Condensed Matter
Replies
3
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
5
Views
1K
  • Atomic and Condensed Matter
Replies
2
Views
1K
  • Atomic and Condensed Matter
Replies
3
Views
819
Replies
1
Views
675
Back
Top