660 



DISPLAY SYSTEM DESIGN PROBLEMS 



Vertical Focusing ^-J^ 



Vertical Deflection 

 Plates 



Fig. 12-38 Thin Cathode Ray Tube Focusing Action. 



neity of the material precludes much optical scattering. The transparent 

 phosphor film is not as efficient as conventional powders but the losses of 

 the transparent phosphor film at high ambient light levels are not as great 

 as for conventional phosphors. 



Various unsuccessful attempts have been made to prepare this phosphor 

 by evaporation. The difficulty in most cases was that either (1) the 

 cathode-luminescent efficiency was too low or (2) the phosphor deteriorated 

 under electron bombardment. However, it has been shown" that the 

 nonluminescent and discolored phosphor film usually obtained when 

 evaporating and condensing most phosphors in vacuum can be made 

 luminescent and transparent by heating the deposited phosphor to a high 

 temperature in a suitable atmosphere. At present, it is necessary because of 

 the temperatures involved in this process to deposit the film on a substrate 

 such as quartz or vicor instead of the glass front surface used in cathode ray- 

 tubes. The film is supported by a metallic clamp near the front face in the 

 tubes presently available. 



I'Feldman and O'Hara, J. Opt. Soc. Am. 47, 300 (1957). 



