Three forms of zinc orthophosphate:manganese have been found. The α form corresponds in x‐ray diffraction pattern to the published values. The luminescence is green, the peak wavelength being 5540 Å. It is produced when manganese concentrations are below 1 mole per cent, or when higher concentrations are not heated above 700°C. The β form has a red luminescence with a peak at 6380 Å. This formation occurs at manganese concentrations above 1 mole per cent and firing temperatures above 800°C. The γ form may be produced by additions of magnesium orthophosphate above 3 mole per cent. The emission is similar to the β form with a peak at 6320 Å, and of somewhat lowered intensity.