atomicproject - 10-8-2008 at 09:45
I am currently working on a homebuilt CRT project. The target screen uses phosphor from a used fluorescent tube. That being the case, the glow is
white. Is it feasible to add a very small amount of copper sulfate to the phosphor to make it glow blue? If not what would be good?
Here is a quick youtube link. The CRT is made from a 250 ml vacuum filtration flask and a test tube for the electron gun. The noise in the background
noise is from the vacuum pump.
http://www.youtube.com/watch?v=nMOjiZR7R6U
Mark
Twospoons - 10-8-2008 at 16:58
The short answer is 'no'. If you read the wikipedia entry for fluorescent lights you will see why.
The best you could do would be to put a blue filter in front of the crt.
Well done, building a working crt!
12AX7 - 10-8-2008 at 17:42
Do you know what pressure that was at? It looks as if you're generating electrons (or positive ions if you're running it backwards!) from a glow
discharge.
Blue, huh? Trying for that Tektronix look? 
Tim
DJF90 - 11-8-2008 at 03:33
Yea I always thought electrons in a CRT were generated by thermionic emission? So what gives the blue glow 
?
watson.fawkes - 17-8-2008 at 09:57
ZnS activated with Ag is the basis for most old blue phosphors. My reference is Handbook of Electron Tube and Vacuum Techniques, by Fred
Rosebury. Potassium silicate is the binder. A small amount of barium acetate aids gelation. A full recipe is in the same volume.
DJF90 - 17-8-2008 at 13:22
I was talking about the electron gun, not the phosphor screen?
watson.fawkes - 17-8-2008 at 14:47
Electrons are electrons. Variations in color come from the chemical composition of the phosphor.