It's called photoexcitation (http://en.wikipedia.org/wiki/Photoelectrochemical_processes)

The incoming photon is absorbed by exciting one of the atom electrons to a higher state. The electron will eventually drop back down and emit the energy back out but in a very predictable way or emission.

The energy does not dissipate throught the diamond because it is converted to an elevated electron shell and the drop down from that level gives you your emmission. There is no ability within that process for energy to move around.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.