High-Luminance And High-Resolution YAG Phosphor Screen In Projection Tube

The dissertation makes a systematic exposition of the theory and technology of a new 3-inch YAG (Yttrium Aluminum Garnet) phosphor screen for projection CRT (Cathode Ray Tube). The phosphor screen having high-luminance and high- resolution has been fabricated by depositing phosphor powder on the YAG substrate (i.e CRT faceplate) using an improved and centrifugal sedimentation methods. The YAG faceplate is sealed to the glass envelope using low-melting-point solder glass. A multi-layer interference filter is applied between the YAG faceplate and the phosphor layer for better picture on the screen of the projection display system. In chapter 1, we describe all kinds of display devices and summarize the state of the art and developing trends of projection display and present the dissertation抯 research task. As the main leading products of large-screen projection display, the CRT projection TVs have been rapidly developed recently. However the performance of luminance, resolution and contrast ratio for conventional projection tube are not perfect. The conventional phosphor screen's faceplate is made of glass whose thermal conductivity is not high, so the accumulation of heat produced by high density electron bombardment causes the phosphor's saturation and degradation, which restricts the improvement of the phosphor screen's luminance. Moreover the glass phosphor screen is large (usually greater than 7 inches diagonal), the corresponding lens for the projection TV has large diameter with high price and the projection TV is weighty and bulky and consumes high power. Therefore we have developed a new 3-inch YAG phosphor screen for projection display. The substrate material (i.e. the CRT faceplate) YAG, replacing conventional glass, has a very high thermal conductivity and optical clarity. The phosphor screen is prepared by depositing phosphor on YAG using improved sedimentation and centrifugal sedimentation screening techniques. Chapter 2 discusses the principle and process for the seal of YAG-to-glass envelope using low-melting-point solder glass. The properties of the material including YAG, glass and solder glass are given; the theories such as the match between the solder glass's expansion coefficient and those of YAG and glass, the solder glass's infiltration to YAG and glass, and the solder glass's re-crystallization are elucidated; the seal techniques consisting of the solder glass's concoction, coating and bake are also described in detail. The experimental results show that the seal has no leak and no stress. Chapter 3 expounds the preparation and performance of the 3-inch YAG phosphor screen. The YAG phosphor screen is composed of a YAG faceplate as the substrate and phosphor powder as the cathodoluminescent material. We fabricate the YAG phosphor screen by depositing phosphor powder on the YAG faceplate using sedimentation improved by us and centrifugal sedimentation techniques, which obtains the high density phosphor layer with good adhesion force between YAG and phosphor and phosphor particles themselves. Phosphor screening is done followed by lacquering, aluminizing. The YAG phosphor screen has the performance of high luminance. As we know, YAG's heat conductivity is more than ten times higher than that of glass used as faceplate in conventional projection tube. Meanwhile the thickness of the YAG faceplate is about one-fifth of the glass faceplate, so the YAG phosphor screen conducts heat much more easily and rapidly than the glass phosphor screen does. The YAG phosphor screen avoids t...