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Coloured Problem

  1. Nov 26, 2006 #1
    Coloured Problem!!

    We know that transition metal ions have unpaired electrons in the outermost shell of the d and f orbitals.
    These unpaired electrons absorb a particular wavelength from visible light and are promoted to higher energy levels. Thus they reflect light of complement wavelength of the absorbed wavelength.
    If the incoming light is white(containing light of all wavelength) and the ion absorbs green light for instance then it would reflect a mixture of red and blue wavlength (i.e. magenta).
    Our eye recongnize the substance as magenta couloured.
    When the electrons come back to ground state, they would emit light of the wavelength previously absorbed(i.e green here). Here I am confused. What the compound would look like? Green or magenta?
    Here how I think about the problem.
    We can resonably assume that the lattice of the substance is composed of a large number of ions. At any instance of time some electrons will absorb light and some other will emit light. Then some portion of the substance would look green and other portion magenta. If both of this happen million of times in a tiny area we will not able to detect distinct colour, rather things will mix up and overally we should see white colour.

    I know there is some flaw in my analysis! What are the flaws?

    Another question:
    Is the exitation and de-exitation of electrons (quantum jump from one orbital to other) is the only reason that gives the subtances the colours they have?
    Does compound other than transition metal have colour?

    Your sensible answer will broad my understanding.
    Thanks in advance.
    Last edited: Nov 26, 2006
  2. jcsd
  3. Nov 26, 2006 #2


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    There are things going on in materials that convert light energy into other forms of energy, particularly vibrational modes that are manifestations of heat energy


    Not all of the light energy that is absorbed is stored in the higher electronic energy levels, so it is not released back into the universe as photons.
  4. Nov 27, 2006 #3
    So does it means that electrons can store energy without promoting to higher electronic energy levels, and they are able to store energy (such as vibrational energy) as they remain in the same energy level.
  5. Nov 27, 2006 #4


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    Electrons do not store energy without being promoted. If they could, we would probably not observe quantum phenomena. The electrons that absorb photons are promoted to higher electronic levels, but they do not necessarily release that energy as photons or as photons of the same energy that they absorbed. There are other mechanisms whereby an electron can lose its energy besides returning to the state from which it was promoted. It is also possible for them to gain energy (be promoted to a higher state) by mechanisms other than photon absorption. A gas discharge tube absorbs energy from electron collisions and releases that energy as photons with the characteristic frequencies associated with the electron transitions.

    There are many possible photon-matter interactions besides the one you initially described of a single photon being absorbed, promoting an electron to a higher state, and then a photon of the same frequency being generated by an electron transition back to its original state. You might not find a satisfying single article on the subject, but if you search for non-radiative transitions you will at least find some indication of the many possibilities.
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