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I know that the color of transition metals is related to the splitting of the d-orbitals. Only a certain wavelength is absorbed in the promotion of electron to a higher d-orbital and therefore the remaining colors are interpreted as a certain color. For example in copper(II) sulphate the red wavelength is absorbed and therefore it the complex appears to be cyan. But shouldn't the same amount of energy be released once the electron drops back to its previous state and releases the energy is gained? What wavelength would this drop correspond to?

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Not necessarily. The drop may occur gradually so that the colour is "blinded out" by the nonadsorbed colours. The drop may also occur in stages, so that several low energy emissions occur. Some are outside visible range and others are too weak or go unnoticed.

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  • $\begingroup$ But if it is due to the d-orbital splitting, shouldn't there be only one possibility of a drop? Where else could the electron go, besides the lower d-orbital? $\endgroup$ – kyczawon Mar 5 '16 at 2:38
  • $\begingroup$ Are you asking about a specific case of splitting or in general? There are a lot of things that affect the energy of an orbital, and there are multiple splitting combinations amongst the metals. $\endgroup$ – Nij Mar 5 '16 at 4:10
  • $\begingroup$ I am asking in terms of a complex that is formed with a ligand. I was taught that the reason why complexes appear to be colored is that their d-orbital splits into a higher and lower energy, and when light is shined through the complex, a certain wavelength is absorbed. But I wonder what happens to the excited electron. If it were to drop to a lower d-orbital it would release the same wavelength as it absorbed... $\endgroup$ – kyczawon Mar 6 '16 at 10:37
  • $\begingroup$ Then the energy levels available are dependent on what metals and what ligands are involved. But there's never just two of them. What would happen if an electron in the lowest level jumped to level 6, then all electrons dropped by one level each? No transition is repeated and yet we absorbed then emitted energy. $\endgroup$ – Nij Mar 6 '16 at 10:56

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