This project aims to develop powder materials (phosphors) with homogeneous ultra fine particle sizes for very high resolution Cathode Ray Tubes (CRTs). These tubes will have significant advantages in brightness, stability, and optical clarity over those currently available. This will bring the European research consortium up and beyond the forefront of this technology.
Freeze-dried powders from the acetate, citrate and sol-gel process calcined in the presence of flux was identical to commercial materials with standard grain size.
For aerosol techniques pneumatic atomisation produced polydispersed samples that resulted in agglomerated powders on calcination. Aerosol generation using pneumatic and ultrasonic atomisation showed considerable promise for preparation of complex phosphor powders with a particle size distribution around 2 um. But although these powders exhibited some powder aggregation on high-temperature calcination they show very low saturation at high current densities.
However by using solvothermal crystallisation the formation of a pure and crystalline garnet-type phase required up to 1000 bars at 500 C. Nearly spherical phosphor particles with diameters from 0.5 to 2.5 um could be prepared. Efficiency and resolution in CRT are good but due to the small particle size agglomeration occurs and the screen uniformity is low.
With solid state reactions the particles are not so close to the spherical shape and the grain size distributions are higher although agglomerates are negligible. Small particle size allows a significant improvement of phosphor screen uniformity and an important decrease of size and numbers of blemishes which results in a better signal to noise ratio of the tube. Luminance and resolution give an improved compromise compared with standard corse grain phosphors or fine jet-milled ones. Saturation is higher than for phosphors from aerosol or solvothermal processes.
OX11 0RA Didcot