I know F-center is a kind of color center, which by definition, is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more unpaired electrons.
But can a f-center be an entire molecule embedded in a solid environment? Or does it only mean the unpaired electron in the solid environment (i.e. alkali halide).
Also, it seems to me the situation is quite similar to a metal center of a metal phthalocyanine, they are both some kinds of impurity and are embedded in a phonon environment. What would be the differences between them regarding their transitions, spectrums and their interactions with the environments?