[McKay (OP)]

I understand fluorescent materials, in normal lightning conditions, look brighter than other materials because they not only reflect their characteristic color directly, but also convert higher energy photons to its characteristic color, right? And since 1 and a fraction of a photon cant be emitted, then the fraction gets dissipated as heat, right?
But what about cases where the incident radiation is actually twice (or more) as energetic as the materials characteristic  color? Do the materials emit two (or more) photons [plus the fraction thats left as heat] or emit just one photon and rest as heat? Or some materials do one and some the other?

[alancalverd]

Yes. That is how we observe x-rays, either by direct fluorescence, by trapping fluorescent photons in a photographic film, or by trapping or counting cascade electrons in a solid. But some materials such as graphite simply convert the photon energy into heat, which provides the primary standard measurement of x-ray dose.

[evan_au]

Yes, that's one of the traditional ways of producing a pair of entangled photons for one incoming photon.
- It produces photon pairs whose energy sums to the incoming photon energy
- Unfortunately, the process is not very efficient
- Even more unfortunately, there is am even smaller fraction of these pairs which are entangled.

See: https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion

[Bored chemist]

Strictly speaking, scintillation, the mechanism by which light is produced from x rays hitting matter, isn't fluorescence.
It's most commonly recombination.
The x ray tears electrons off the material and as those electrons get back to where they belong, they emit light.
There's also this
https://en.wikipedia.org/wiki/Auger_effect

In fluorescence stricto sensu, the molecule holds together during the process and no free electrons are involved.

[alancalverd]

So fluorescence should be restricted to nonionising radiation. Neat pedantry, but you won't get far in a radiology trade exhibition if you tell every manufacturer that they are lying!

However it does, presumably, apply to fluorescent lighting where the mercury UV spectrum excites all sorts of electron mechanisms in zinc compounds, and in Seventies discos where your sweaty nylon shirt lit up with the residues of Daz.

Now that's got me thinking. The Residues of Daz could be a prog rock band, or the hideout of the interstellar resistance movement after a cosmic war. What to pick up next - guitar or word processor?

[Bored chemist]

Using the right words isn't considered "pedantry" in science. By all means get it wrong at a trade exhibition; but don't call it fluorescence in a science exam.
Some, but not all, of the light from fluorescent lights is actually fluorescence. Quite a bit is phosphorescence.
That's why that coating inside the lamp is called a phosphor...

[alancalverd]

As indeed is the stuff inside a fluoroscope!