Why does light transmit through glass/diamond, but not solid

  • #1
I am getting my head around energy bands in electrons, valence bands, and conduction bands, but its complicated to understand.
But If if I ask the question this way it is more simple to me.
Photons pass through the material because they don't have sufficient energy to excite a glass electron to a higher energy level.
Energy levels exist together in regions known as energy bands.
In between these bands are regions, known as band gaps, where energy levels for electrons don't exist at all.
Some materials have larger band gaps than others.
In glass, or a diamond the material is solid but light can transmission through, no problem.
In a solid carbon block in the picture below, light gets absorbed.
So a object being amorphous (noncrystalline) does not effect transmission, its the energy.
If an electron is in the first energy level, it must have exactly -13.6 eV of energy. If it is in the second energy level, it must have -3.4 eV of energy.

Let's say the electron wants to jump from the first energy level, n = 1, to the second energy level n = 2. The second energy level has higher energy than the first, so to move from n = 1 to n = 2, the electron needs to gain energy. It needs to gain (-3.4) - (-13.6) = 10.2 eV of energy to make it up to the second energy level.
If it is in the second energy level, it must have -3.4 eV of energy.
Let's say the electron wants to jump from the first energy level, n = 1, to the second energy level n = 2. The second energy level has higher energy than the first, so to move from n = 1 to n = 2, the electron needs to gain energy. It needs to gain (-3.4) - (-13.6) = 10.2 eV of energy to make it up to the second energy level.
If it takes 10 eV to move the electron in shell 2 , in the glass, and the iron block, then why does the glass electron not get excited when hit by a photon.
Why is the carbon electron absorbing, I understand its a solid, and dense, but so is glass, and the diamond just as much.
I am almost sure its the energy, or the electrons not the amount of electrons in the shells of the carbon because carbons has 2 electrons in shell 1, and 4 electrons in shell two, silicone which is mostly what glass is made from has two electrons in shell 1,and 8 in shell 2, and 4 in shell 3.
So with silicone having more electrons it cannot be the reason for absorption, so its the energy of the electrons right
So it cannot be the amount of electrons I think just the energy of electrons, but can you explain why the energy levels are different for some electrons.
So an object being transparent cannot really be about how many electrons in its shells right,
BUT, every electron is every atom needs 10.2 eV of energy to make it up to the second energy shell level, to leave the ground state, doesn't it.
This is why I am confused, if glass electrons do not need 10 eV to move to the next shell level why is this.
Thank you for your help, remember I am still learning, sorry if some things are not accurate.


Glassy_carbon_and_a_1cm3_graphite_cube_HP68-79.jpg
 

Answers and Replies

  • #2
ZapperZ
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Again, you are mixing up ATOMIC ENERGY LEVEL and SOLID STATE ENERGY BANDS. It is confusing to figure out oif you are asking about atomic gasses or solid media. In the BANDS, there is no such energy state as a distinct 13.6 eV line!

In a metal, there are electrons in the conduction band need only an infinitesimal amount of energy to be excited, because it is sitting in a continuous energy band with unoccupied energies.

You really need to learn about solid band structure here. And stop making new threads on the same topic that you have already been asking!

Zz.
 

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