Re: Electrons exciting materials to emit light.

The accelerating field in a CRT is usually around 1 kV, so the electrons
are going to achieve kinetic energies of order 1 keV.  Now the typical
energies of visible-light photons are around 2 eV  (you can work this
out by using E=hc/lambda and remembering that 1 eV = 1.6e-19 J).  So
it appears that each electron is likely to collide with and excite
many atoms/molecules when it hits the screen.  More electrons or 
more energetic electrons are therefore going to result in more intense
light (but wavelength of the light shouldn't change since it involves
decays between fixed energy levels).

In the case of the photoelectric effect, the incident photons have
energies close to the ionisation energy for the material in question,
and the fundamental observation is that no electrons are emitted until
the photon energy reaches this threshold (irrespective of the numbers
of photons).  If in a CRT you reduced the electron energies down below
that required to raise electron levels in the phosphorous screen, 
then you'd presumably find similar behaviour.