Process for producing europium activated stronium tetraborate uv phosphor

Abstract

A europium activated strontium tetraborate UV emitting phosphor is disclosed having a weight composition of from about 34.72% to about 35.80 strontium %, from about 17.66% to about 17.78 boron %, from about 0.37% to about 1.86% europium, and the balance oxygen. The phosphor has essentially elongated prism-like particles with the europium relatively uniformly distributed throughout the balance of the phosphor and with the particle size distribution being characterized by the 50% size being in the range of from about 7 micrometers to about 12 micrometers as determined by Coulter Counter measurement and with less than about 12% by weight of the particles having a particle size of greater than about 16 micrometers as determined by Coulter Counter measurement. The process for making the phosphor is disclosed which involves forming a mixture of strontium oxide and europium carbonate in an aqueous solution of boric acid at a temperature of at least about 70.degree. C. with the mole ratio of SrCO.sub.3 to H.sub.3 BO.sub.3 being from about 1:4 to 1:4.5 and the Eu.sub.2 O.sub.3 content being from about 0.003 to 0.015 moles. The mixture is digested at at least about 90.degree. C. for a sufficient time to form a solid precipitate comprising a strontium borate hydrate intermediate and a liquor, followed by separating the solid from the liquor, drying the solid and firing the solid in an atmosphere of 0.3% to 3.0% by volume hydrogen and the balance nitrogen at at least about 800.degree. C. for a sufficient time to produce the phosphor.