Image Number 5 for United States Patent #4440831.
Improved zinc silicate phosphor particles are made by using silicic acid particles in the range from 0.7 to 10 micrometers coated with Mn.sub.2 O.sub.3 .multidot.xH.sub.2 O and then a layer of ZnO particles about an order of magnitude smaller which are fired to form the phosphors. The particle size is held within the range preferred and preferably is even narrower. The particles are not milled or mechanically crushed. Instead, the ZnO powder prevents agglomeration during firing. Baths are provided for formation of the particles prior to firing. Brightness and persistance are improved over conventional phosphors.