Rhodamine 6G (Freaking laser beams)

As I've discussed in the past, certain dyes can detect radiation, stain DNA, sense solvent polarity, or (in olden times!) color the Chicago River green. This one can make a laser!

With sufficiently fluorescent dyes, you can actually take a laser and use it to "pump" a jet of a dye that absorbs the laser wavelength, and get a longer (lower energy) wavelength out. This often makes a mess - rooms with dye lasers seem to make it about five minutes before someone spills one of these day-glo lasing mediums on the floor.

MoTD science club: here's a polycarbonate bottle cast with a pink dye with an absorption (and emission) spectrum pretty close to that of a dye like rhodamine 6G (which I imagine it's not, it being pretty water-soluble and toxic). It's being hit with a 532 nm Nd laser, which matches up with its absorption spectrum. The emission spectrum is broad, and it comes out orange overall.

The green line on the wall to the left is reflected light; the green dot on the wall behind the bottle is transmitted light; and the orange dot on the bottle is where the beam enters -- this is the fluorescence of the dye in the plastic.

Fluorescence is always longer wavelength (lower energy) than the excitation light. Since you can't see IR, red laser pointers won't really make anything light up. If you have a green one (or a crazy expensive blue one!), try pointing it at red-orange-yellow stuff. Hot pink stuff is just about guaranteed to work.