DISPLAY TUBE WITH MULTILAYER INTERFERENCE FILTER

摘要

16 "Display tube." A display tube comprising in an evacuated envelope (1) a display screen (7) provided on the inside of a display window (2) in the wall of the envelope (1), which display screen (7) comprises luminescent material (13), and a multilayer interference filter (12) is provided between this material and the display window and comprises a number of layers (HL) which alternately are manufactured from a material having a high (H) and a material having a low (L) refractive index. If the filter is composed substantially of 14 to 30 layers, each having an opical thickness nd, wherein n is the refractive index of the material and d is the thickness, which optical thickness is between 0.2 .lambda.f and 0.3 .lambda.f and preferably between 0.23 .lambda.f and 0.27 .lambda.f, wherein .lambda.f is equal to p x .lambda., wherein .lambda. is the desired central wavelength which is selected from the spectrum emitted by the luminescent material (13) and p is a number between 1.18 and 1.36, a display tube is obtained in which the luminous efficiency in the forward direction and at small angles for the central wavelength of the phosphor is at least 40.degree. largerthan in a tube without such a filter. Colour improvement and gain in contrast also occur.