The process of fluorescence results in "fluorescent compounds" accepting
energy at specific wavelengths. This raises them to a higher energy
level causing electrons to shift into a shell closer to the nucleus. The
resultant state is very unstable and electron pass back to the outer
shell again. In passing back some energy is given off. As this is at a
lower energy than the original wavelength of light used, the energy
emitted is at a lower energy (therefore a longer wavelength and often a
different color). This process gradually ceases. The rate at which it
ceases depends on multiple factors, a major one being the nature of the
fluorchrome itself.
I really  have no idea how X-rays can affect fluorescent labels but can
procrastinate some (no comments please). I assume that X-rays  can cause
a breaking of the fluorescent  label from any associated antibody or
protein to which they have bound. X-rays in sufficient doses have been
shown to have a cross linking effect on proteins such as collagen.
X-rays will however generally not be of an excitatory nature to the
fluorchrome. Even if they were, the wavelength emitted would still be in
the "invisible" part of the spectrum.
Barry

John Baker wrote:

> One of our post-docs here has two questions concerning fluorochromes
> and x-rays. They are:
>
> 1.  How, if at all, do x-rays affect fluorochome labels?
> 2.  What is the mechanism that causes fluorochromes to lose their
> excitability when exposed to normal spectrum light?
>
> Thanks in advance,  John
>
> --
> John A. Baker
> The University of Michigan
> Orthopaedic Research Laboratories
> Histology Unit
> 400 North Ingalls, G160
> Ann Arbor, MI 48109-0486
> Main lab office phone:734-763-9674
> Histology office:734-936-1635