[lancenti]

I've been thinking a bit about this, and probably it seems like such an odd question, but I'm really genuinely wondering why it is that we can see colour. Now, I'm not thinking about the cones and rods in our eyes, but rather the mechanism by which we 'see' colour in transition metal complexes.

From what I've learned, colour is a phenomenon caused by light in the visible spectrum being absorbed by an electron to promote itself from one electronic state to another of the appropriate energy. This results in us seeing the complementary colour of the light that was absorbed.

Now, oversimplifying the situation to three identical atoms, suppose I shine white light (for ease, a mix of 400-700 nm to limit it to the visible spectrum) on the sample of three atoms. At some time t, the first atom which I will call A absorbs the photon so we see the colour. Some time after that, atom B absorbs another photon so we see colour again. But following this, a few things may happen:

1. Atom A de-excites while atom C absorbs -> no net 'loss' of photon since one is absorbed whilst one is released.
2. Atom A de-excites without atom C absorbing -> I should see the colour absorbed, and not its complementary colour

So in both cases, I don't see the 'correct' or expected colour, although experience tells me that's nonsense. I figured that maybe it's because it's too fast for our eyes to see. However, it doesn't really make sense to me because if it will forever appear as some colour, there can be no equilibrium / equal rate of exchange between the two states otherwise it'll end up like case 1 and I should see white. But if equilibrium is not achieved, then the object absorbing should eventually achieve some sort of population inversion and stop absorbing a certain colour effectively. Either case suggests that I should not see colour, or that an object will absorb different colours if subjected to light long enough.

Clearly something is wrong with my reasoning, but I can't seem to catch it. If anyone can point me into the right direction, I would greatly appreciate it.

[Borek]

Whatever has been absorbed is emitted in the random direction, thus passing light seems to be filtered.

[Jzalkm]

i read somewhere (has to look for solid reference) that the 'de-excitation goes through another pathway. hence radiation not emitted during 'de-excitation'.