Process for improving the luminescence and bulk density of niobium activated yttrium tantalate X-ray phosphor

Claim 1

A process for preparing a M' YTaO 4 :Nb X-ray phosphor having a coating of silicon dioxide, said process comprising: (a) forming a uniform mixture consisting essentially of Y 2 O 3 , Ta 2 O 5 , and Nb 2 O 5 components, and a flux selected from the group consisting of lilthium chloride, lithium sulfate and a mix of lithium sulfate and potassium sulfate the mole ratio of lithium sulfate to potassium sulfate in said mmix being about 80 to 20, wherein said flux makes up from about 25% to about 50% by weight of said mixture, said components being provided in an amount equal to approximately the stoichiometric amounts required to form said phosphor; (b) firing said mixture in a furnace by heating said mixture in said furnace from a temperature of about 300° C. to a temperature of from about 1200° C. to about 1300° C. at a heating rate of from about 1.0° C. per minute to about 1.5° C. per minute and maintaining said temperature for from about 10 hours to about 14 hours to react said components and produce a fired material containing luminescent material; (c) cooling the resulting fired material by turning off the heat to said furnace and allowing said fired material to remain in said furnace until the temperature in said furnace is no higher than about 300° C.; (d) washing the resulting cooled material with deionized water to remove essentially all of said flux therefrom and produce a washed M' niobium activated yttrium tantalate phosphor; (e) removing the wash water from and drying said washed phosphor; (f) classifying the resulting dried phosphor to obtain a -325 mesh particle size in said phosphor; (g) forming a uniform blend consisting essentially of the resulting classified phosphor and silicon dioxide wherein the amount of said silicon dioxide is from about 0.01% to about 0.1% by weight of said blend, and wherein said silicon dioxide has a particle size of less than about 1 micrometer in diameter; and (h) dry milling said blend to produce a silicon dioxide coated phosphor having a bulk density of at least about 50% greater than said classified phosphor produced absent said coating and having a luminescence improvement of at least about 4% over said classified phosphor produced absent said coating.