Osram Sylvania Inc.

Gte Products Corporation

Cheryl M Forster

Anthony F Kasenga

Ronald E Karam

Vaddi B Reddy

James R Cox

Chung N Chau

Joseph A Cooper

Scott A Meilicke

Barry G DeBoer

Phosphor lag was reduced to acceptable levels in high lag monoclinic M' yttrium tantalate x-ray phosphors through the addition of minor amounts europium to the phosphors. In particular, europium was added to yttrium tantalate phosphors containing terbium and to phosphors formulated with a stoichiometric excess of yttrium.

Reduction of lag in yttrium tantalate x-ray phosphors

A pure gamma calcium pyrophosphate for use in e.g., the production of calcium haloapatite fluorescent phosphor host materials, and a process for the synthesis thereof. Dicalcium orthophosphate is dissolved in a dilute solution of nitric acid in water, and spray-dried to form a calcium phosphate powder including a major phase of spherically shaped particles of dicalcium orthophosphate. The calcium phosphate powder is fired in air to convert the calcium phosphate powder to pure gamma calcium pyrophosphate. Gamma pyrophosphate will not undergo dehydration during firing of the fluorescent phosphor; thus larger quantities of phosphor can be processed in a firing vessel.

Synthesis of gamma calcium pyrophosphate

A process for producing a manganese activated zinc orthosilicate phosphor. An aqueous dispersion is prepared including fumed silica having an ultrafine average particle size of less than 50 nm, a zinc precursor, and a manganese precursor. The molar ratio of zinc:silicon in the dispersion is approximately 1.3:1 to 2.0:1, and the molar ratio of manganese in the dispersion is sufficient to activate the phosphor. The precipitate from the dispersion is calcined in an inert atmosphere at a temperature and for a time sufficient to form a manganese activated zinc silicate phosphor having a broad band emission peaking in the green region of the visible spectrum when stimulated by external radiation at approximately 254 nm. The calcined phosphor may be milled to achieve an average particle size of less than 5 .mu.m, the milling step being performed without significant loss of plaque brightness. Also disclosed is a green emitting manganese activated zinc silicate phosphor having an average particle size of less than 5 .mu.m and excellent brightness.

Method of preparing manganese activated zinc orthosilicate phosphor

A process for producing a manganese and lead activated calcium metasilicate phosphor having the nominal formula CaSiO.sub.3 :MN:Pb. The process involves preparing a uniform aqueous dispersion of fumed silica having an ultrafine average particle size of less than 50 nm, a calcium precursor, a manganese precursor, and a lead precursor. Preferably, the calcium, manganese, and lead precursors are added as powders to an aqueous dispersion of said ultrafine fumed silica. The ultrafine fumed silica aqueous dispersion is heated to a temperature of about 50.degree.-90.degree. C. and the powders are mechanically dispersed in the fumed silica aqueous dispersion to form the uniform aqueous dispersion. The molar ratio of calcium:silicon in the mixture is approximately stoichiometric to 1.3:1; and the molar ratios of manganese and lead in the dispersion are sufficient to activate the phosphor. The precipitate from the dispersion is calcined at a temperature of about 1050.degree.-1135.degree. C. for a time sufficient to form a manganese and lead activated calcium silicate phosphor having a peak emission in the red region of the visible spectrum when stimulated by external radiation at approximately 254 nm. The phosphor product has an average primary particle size of less than 5 .mu.m and a brightness at least equivalent to that of commercially available manganese and lead activated calcium silicate phosphors.

Method of preparing manganese and lead coactivated calcium silicate

A method of making lead-activated barium silicate phosphor involves the use of a lead source which is not lead oxide. More particularly, the lead source may be lead silicate or lead carbonate-lead hydroxide.

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Van Etten, NY, United States of America

Cheryl M Forster