Rare earth activated strontium lithium germanate phosphors

摘要

A phosphor composition is of the formula uSrO.w/2(Li2O).yGeO2 : z(Tb or Eu) wherein 0.65 sE u/y sE 2.6; 0.1 sE w/y sE 2; 0.04 sE z/y sE 0.2; preferably 1 sE u/y sE 1.8; 0.5 sE w/y sE 1.5; 0.08 sE z/y sE 0.12 where u, w, y, z are gram atoms of the elements in the composition. Optimum output is produced when the total positive charges of strontium, lithium and the activator elements equal the total positive charges of germanium i.e. when 2u + 1w + 3z ­ 4y, when for the above preferred composition u = 1.29; w = 1; z = 0.108 and y = 1. 254 n.m.U.V excitation produces line emission output of 550 nm. and 620 nm. for Tb and Eu activated phosphors respectively and similar green and red emissions by electron excitation allowing use in fluorescent lamps and colour TV. In a method of preparation, the raw mix is fired at a temperature from 900 DEG C. to 1250 DEG C. preferably 1150 DEG C., 1000 DEG C. and 950 DEG C. for lithium concentrations of 0.2, 0.6, and 1.0 respectively, for from 1 to 3 hours, preferably 2 hours. Preferably the firing is interrupted after one hour to grind the phosphor raw mix. When Tb is activator a firing atmosphere of nitrogen or nitrogen with 2% vol. hydrogen is employed, with Eu activator, an oxygen or air atmosphere.