Fluorescence? Does it only happen once?

If a solution is excited and fluoresces, such as a tracer dye solution (Rhodamine for example), can it fluoresce again if excited or can it only happen once ?

Basically, when you expose a fluorescent compound to the light of excitation wavelength, meaning it is the wavelength of light characteristic for that particular compound, the electron in the compound absorb that energy (i.e., get excited) and move to higher energy orbit.  As long as that compound is continually excited, they will remain in that state.  This is because the excited electrons are not stable and would like to return back to the ground or zero energy state, they do this by emitting the absorbed energy as fluorescence.  Since the compound is in this case, continually exposed to the light of excitation wavelength, the cycle keeps repeating for continued fluorescence.

If you stop the exposure, then the electrons would simply give off the absorbed light as fluorescence and return back to the ground state and will remain so until they are excited again.

Basically, the compound will absorb the light of a shorter wavelength and emit the absorbed light of a higher wavelength.  Thus the emission wavelength is always higher in terms of no. than the excitation wavelength.