DOUBLE AND TRIPLE ACTIVATED MAGNESIUM PYROPHOSPHATE PHOSPHORS 1

Magnesium pyrophosphate, double activated with cerium and thorium, has been developed as an ultraviolet emitting phosphor having con-siderably greater powder brightness than standard 360 BL phosphor. The peak of emission occurs between 3440 and 3560.~, depending upon composition, as compared with 3600 i for 360 BL. All data refer to excitation with k 2537. With increasing thorium content, the brightness is increased and the peak emission displaced toward longer wavelengths. The increase in brightness compared with the single activated parent phosphors is more than additive and may be interpreted as being due to sensitization of Th by Ce. The phosphors are made more friable through addition of a few per cent of silica before firing. They are very susceptible to oxidation at elevated temperatures and, for this reason, have not given outputs in lamps as high as expected from powder brightness data. The further addition of manganese r sulted in a novel system of triple activated phosphors, Mg~P2OT: (Ce, Th, Mn), with relatively bright emis-sion in the visible, plus variable amounts of ultraviolet. Color and bright-ness of these phosphors are a function of the concentration of all three activators, as shown in graphs and tables. The maximum brightness attained so far was of the order of two-thirds of that of ZnBeSilicates of corresponding color. These phosphors, too, are improved by silica and show high sensitivity to xidation at elevated temperatures. They pro-duced lamps of lower lumen output han was expected from powder bright-ness data