> > For example in the yellow fluorescent dye =93rubrene=94 both violet and=
 green
> > lasers will activate it and glow yellow. This proves you don=92t always=
 need
> > ultraviolet light. But a red laser will not activate a yellow dye. Why =
is
> > that?"

Question was by original source and not poster.

Wavelength of photons (if particles can have a wavelength)(they
can)(sort of)  must be shorter than the wavelength of the emitted
light.
Energy available to 'kick" electrons up to a higher energy level must
be higher than the energy emitted when they decay to prior state.

For extra points contrive system that uses multiple 'jumps' to get
electrons to a state where the decay energy is greater than  energy in
single pumping photon.

Warning! - do not let over-unity people see this or they will be off
on another tangent. :-)


R

--=20
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