This question seems simple but I don't seem to find many answers right away for this.
When you make a crystal doped with ions (like a luminescent phosphor) and the ions then become a defect in the crystal structure and still have emission lines similar to the free ion, is that ion really free? Or is it actually in some kind of bond?
I mean, if it did make a ionic or molecular bond, it wouldn't be a free ion anymore, the energy levels and the probabilities for the electron transitions would be very different, but the crystal has a luminescence that's similar to the free ion.
Of course there will be interactions, the electron transitions won't have the same probabilities of the free ion (you do see some lines of emission been strengthened, weakened and/or shifted when you use a same ion in different crystals), but it's quite similar in the overall.
Saying the kind of defect an atom is on a lattice (like interstitial or substutional) only tells me about the geometry and array of the atoms on the lattice.
But I want to know about the chemical bonds they're making (or not).
Are they just "trapped" inside the structure by electrostatic repulsion without making an actual bond with any molecule around them?