Novel YAG phosphor screen for projection CRT

It is found that the deterioration of the projection phosphor screen is accelerated by phosphor screen heating. Therefore, a critical step in the development of projection tubes of greater luminosity is the improvement of the phosphor deposition method that results in a higher thermal conductivity of the phosphor layer. We have developed a novel phosphor deposition technique for YAG projection display applications. YAGG:Tb phosphor powder is mixed with 30wt% H2SO4 solution, deposited uniformly on YAG substrate and then heated at 500 degrees C for about Ih in a flowing air atmosphere. XRD and SEM analyses show that a sulfate phase is formed. It serves as a binder and increases the contact area between adjacent YAGG:Tb particles and between YAGG:Tb particles and YAG substrate. The luminance characteristics of the new phosphor screen are studied by a demountable apparatus designed to simulate the tube condition. Aging tests are carried out with the accelerating conditions as follows: 20KV, 0.2mA electron-beam scanning a 10 x 20mm(2) area. Compared to the YAG phosphor screen prepared by conventional sedimentation method, the new screen offers an improvement of 5% in the luminance at cathode current density of 30 mu A/cm(2) and anode voltage of 28KV Moreover, no color shift is observed. The deterioration luminescence efficiency due to electron bombardment can be reduced by about 10%.