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  1. Jul 3, 2011 #1

    I am trying to figure out how does the Ti4+ Fe2+ charge transfer complex produces the blue color of sapphire quantitavily... as it is given here:


    How is it possible to calculate that this particular charge transfer requires absorption of "yellow light (~2eV)" giving rise to the complementary blue color, using very simple quantum physics because I am no expert ???

    Is it possible to use bohr model and simple electromagnetism???

    I will highly appreciate your contributions.
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Jul 8, 2011 #2


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    That is not possible. Experts at computational chemistry for solids may be able to do this calculation, using lots of hardcore many-body physics and big computers, but even they would need to pull tricks[1]. And I still wouldn't bet on them being able to get quantitative agreement, let alone predictions. Using simple methods and not being an expert, I'm afraid you have no chance.

    [1] The most commonly applied method for calculating excitation spectra, (linear-response) time dependent DFT, is not applicable to charge transfer excitations.
    Last edited by a moderator: Apr 26, 2017
  4. Jul 8, 2011 #3


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    Holy capslock Feynman.
  5. Jul 9, 2011 #4
    Thank you for the reference to this paper. It is very clear and I long needed it.
    The principle is easy to understand, the detailed calculations are beyond reach.
    The principle is the same as in organic dyes : an electron can delocalize with oscillation between two distant and prefered zones of the molecule or the crystal. So the frequency of the oscillation is in the range of human-seeable band, and this electron can absorb several quanta at this frequency and thermalize them by mechanical means towards the lattice and its phonons, before reemitting a photon by optical way.

    Colour is a property of the human system of sight (human retina, human wiring of the retina, human visual cortex), not of the light or the objects under light.
    Last edited by a moderator: Apr 26, 2017
  6. Jul 9, 2011 #5
    I am trully stunned!!!!!

    Actually I am a student of material science & I have been encountering such phenamena recently...

    I am intrigued to know; what are the commonly applied methods for calculating excitation spectra???
  7. Jul 9, 2011 #6
    You reminded me of QED :)

    Is it possible to use QED in this case????
  8. Jul 9, 2011 #7
    Color is undoubtedly a magnificant phenamena to study from the scientific perspective... A combination of physics, chemistry, biology & so on ....

    The hope diamond has a band gap of 0.4 eV due to Boron doped in its structure... How can the 0.4eV can give rise to blue diamond!!!!!! just cant get this????!!!!
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