Absorbing inhomogeneous film for high contrast display devices

A luminescent display device comprising a transparent viewing portion, a phosphor layer on the interior surface of said viewing portion, a light absorbing inhomogeneous film covering and adherent to said phosphor layer and excitation means for causing said phosphor layer to luminesce, said inhomogeneous film having a tapered composition varying continuously from a metal oxide at the phosphor-film interface to the metal constituent of said oxide facing said excitation means such that said film exhibits a continuous gradient of refractive index from an index approximating the index of said phosphor at the phosphor-film interface to an index approximating the index of said metal, and said metal oxide being selected from the group of oxides consisting of tantalum oxide and vanadium oxide.

A method for making a viewing screen for luminescent display devices consisting essentially of the steps of:

• forming a luminescent phosphor layer on a transparent substrate, and
• forming a light absorbing inhomogeneous film on said phosphor substrate, said film having a tapered composition varying continuously from a metal oxide at the phosphor-film interface to the metal constituent of said oxide at a point remote from said interface such that said film exhibits a continuous gradient of refractive index from an index approximating the index of said phosphor at the phosphor-film interface to an index approximating the index of said metal at said remote point and said metal oxide being selected from the group of oxides consisting of tantalum oxide and vanadium oxide.