Phase Equilibria and Manganese-Activated Fluorescence in the System Zn[sub 3](PO[sub 4])[sub 2]-Mg[sub 3](PO[sub 4])[sub 2]

Determination of the phase relationships on the join by the quench method has enabled the previously designated "gamma zinc phosphate" to be identified as a solid solution of zinc orthophosphate in magnesium orthophosphate. takes 95 mole % into solid solution at 1000°C. takes a small amount of into solid solution (about 3 mole % at 1000°) and, in order to satisfy the requirements of the Phase Rule, must take a small amount of into solution. The previously determined relationships are discussed in terms of the new data for the zinc‐magnesium orthorphosphate system. Solid solution relationships in the system are diagrammed and discussed. Data on peak emission and brightness of the solid solution and the solid solution were obtained using molar substitutions of manganese as an activator. The brightness of the solid solutions compares favorably with commercial phosphors and the N.B.S. standard. The manganese‐activated phosphors near the high zinc end of the solid solution series are very bright relative to the standard, but they peak near 6280Aå, which may in part account for the higher brightness.