PHOSPHOR DEVELOPMENT FOR ALPHA-SILICON LIQUID-CRYSTAL LIGHT VALVE PROJECTION DISPLAY

This paper describes the development of a phosphor suitable for efficiently activating an alpha-silicon photoconductor. The photoconductor is employed to modulate a liquid crystal layer for use in a real-time television projection system. A thorough evaluation of available phosphors disclosed their unsuitability for this use. The major requirement for this material is that: the spectral emission closely match the alpha-silicon responsivity curve, have sufficient radiance to activate the photoconductor efficiently, be resistant to thermal degradation, and exhibit fast decay. An yttrium aluminum oxide phosphor with the yttrium aluminum garnet (YAG) crystal structure and activated by chromium satisfied the above requirements. The process of making this phosphor is described with emphasis on producing the YAG phase by the most practical means. Products were evaluated for radiance, spectral distribution, crystal structure, decay time, and ease of screen preparation.