I searched for it but couldn’t get anything.
I know that if some material is a shade of green colour then light of every other wavelength other than that shade is absorbed.
Also that the colour appears due to the visible electromagnetic radiation by de-excitation of electrons.
What I don’t understand is:
Why do electrons keep oscillating between higher and lower states?
Electrons can move from one level to another level by emitting photons of different energy. For example for level 5 to level 1, it can go 5->3->1 or 5->4->3->2->1. So why is the apparent colour consistent?
A blue pigment absorbs yellow light. So electrons absorb yellow light to excite but give off blue when de-exciting for the same transition. How does this hold conservation of energy?
Would there be any observed colour difference if the same light bulb is kept in a blue room with blue objects and then a yellow room with same blue objects?
Thanks for helping.
In: Chemistry
> A blue pigment absorbs yellow light. So electrons absorb yellow light to excite but give off blue when de-exciting for the same transition.
No. A blue pigment absorbs yellow light and *reflects* blue – it doesn’t emit blue.
But the behavior you’re describing, of single discrete energy levels that are constant for each atom and no other means of dispersing energy, only apply to *isolated* atoms. An atom in a low-density gas way out in space does behave that way, and so a 1->4 transition would either go 4->3->2->1 or 4->3->1 or 4->2->1 or 4->1 (emitting higher-wavelength light in the first three cases).
But atoms in materials have other ways to disperse energy. They have internal higher-energy states, centered around things like the spin-orientation of their electrons (although these states tend to decay pretty quickly). They have strong bonds to other atoms in the same molecule that are somewhat ‘elastic’ and can absorb energy by stretching or twisting. (This is how the proteins that detect light in your eyes work – they have a bond that twists when they absorb a photon.) They have weak bonds to the overall structure of their parent material that can do the same. And so on. So an electron can absorb energy but then release it in forms other than photon re-emission.
If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it into vibrational motion.
During its vibration, the electrons interact with neighboring atoms in such a manner as to convert its vibrational energy into thermal energy. Subsequently, the light wave with that given frequency is absorbed by the object, never again to be released in the form of light. So the selective absorption of light by a particular material occurs because the selected frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate.
Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.
>Electrons can move from one level to another level by emitting photons of different energy. For example for level 5 to level 1, it can go 5->3->1 or 5->4->3->2->1. So why is the apparent colour consistent?
It wouldn’t be. The energy of the photon would correspond to the energy of one transition. So going straight from 5>1 would lead to emission of one large energy photon. Making 5 steps down to level 1 would lead to the emission of 5 lower energy photons, probably with different energies each. Because energy is related to wavelength, they would have different colours.
You can’t move from one level up to another by absorbing a yellow photon and down from the same level to the original by emitting a blue one. But because there are lots of different energy levels within atoms or molecules. It’s possible for the same atom to emit or absorb photons of different colour. So an atom could absorb a high energy blue photon and jump from level 1 to level 5 and then emit a lower energy yellow photon and drop back down to say level 3.
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