Why does the phosphor glow ? (And something about black screens)

May seem like a stupid question, but I got myself into a discussion about CRT projectors and black screens in a local newsgroup.


My gut feeling was that a black screen wouldn't work with CRT projectors, due to their relatively low light output, but another poster is under the impression that it would be an ideal match. According to him, the light in a CRT is generated when electrons in the phosphor's atoms fall back to their normal energy level, after being exited by the electron beam. This should result in CRT projectors generating three very specific wavelengths of light, as the energy level jump of the electrons would correspond to a photon of one specific wavelength (sounds like laser, doesn't it ?). In turn, this would be ideal for a black screen, as they supposedly reflect only specific wavelengths of light and absorbs all others.


I've been trying to verify this information, but all the sources I've frequented only mentions that the phosphor 'glows' when it is hit by the electron beam, but doesn't go into detail about the actual physical process taking place. The fact that the phosphor turns brown with wear, suggests to me that there must be a chemical process taking place too.


Also, earlier ramblings in this forum about 'laser-CRT' and the purity of color it would provide, seems to indicate that current CRTs are not that pure in color.


So, can anyone shed light on this and perhaps comment on the feasibility of using a black screen with CRT projectors ?


Cheers,

Erling