Abstract: This invention provides a process for forming a phosphor screen of a monochrome cathode ray tube (projection tube) which has an improved luminance remaining property. The phosphor particles are settled on an inner surface of a glass bulb with a binder of SiO.sub.2 to form a phosphor layer, in which the amount of SiO.sub.2 is reduced by rinsing with a water-based liquid like deionized water and a PVA solution before forming an organic layer on the phosphor layer. The phosphor screen has an improved luminance remaining property that is close to that of a direct viewing color cathode ray tube, without lowering the screen quality.

Abstract: A method for forming a very fine phosphor screen of a monochrome cathode ray tube whose roughness is inconspicuous even if the picture is enlarged. White phosphors (P45) whose average particle diameter D by a dry method is 1.5 .mu.m, ethanol, and ammonia water are stirred and maintained at 50.degree. to 55.degree. C. A mixed solution of ethyl silicate and ethanol as well as ammonia water are separately dropped into the mixed solution containing the phosphor particles (P45). After standing still, the supernatant liquid is removed by decantation, and the precipitates are dehydrated, and dried by heating, and sieved to obtain white phosphors (P45) whose surfaces are coated with silicon dioxide. Such phosphors satisfy 1D.ltoreq.d.ltoreq.1.3D, in which "D" represents an average particle diameter measured by a dry method, and "d" represents an average particle diameter measured by a wet method. Therefore, the phosphors have excellent dispersion property in a suspension.