Colour cathode ray tube.

摘要

Phosphors used in colour cathode ray tubes, particularly but not exclusively, projection television tubes, should have colour point standards or chromaticities conforming to European Broadcasting Union (EBU) standards. The widely used blue light emitting cathode ray tube ZnS : Ag phosphor which conforms to EBU standards has the disadvantage that its efficiency at high beam currents is low and in consequence limits the white-D luminance of projection television systems. Many blue light emitting phosphors exist which are more efficient than ZnS : Ag at high beam currents but which have the disadvantage that their chromaticities do not conform to EBU standards because the y-value in the CIE colour triangle is too high or too low. This disadvantage can be overcome by disposing an interference filter which has a peak gain greater than unity over a selected part of the frequency spectrum in the light-path from the phosphor for example between the phosphor and the faceplate. As a result of using an interference filter an efficient broadband phosphor can be employed to obtain the desired chromaticity and thereby increases the white-D luminance of projection television systems.