REFERENCES

The preparation and properties of the Group II metal pyrophosphates ac-tivated by tin are described. It is shown that the fluorescent emission is strongly dependent on the matrix shifting tow'ard higher wave lengths with increasing size of the cation of the pyrophosphate. Excitation and emission spectra of many of the phosphors are given. The most useful of these phosphors is Sr~P207: Sn, a very efficient blue phosphor emitting at 452 m~. During the past few years there have been several investigations of t in-act ivated phosphates. These phosphors present certain problems in preparat ion since the tin atoms function as activators only when in a part ia l ly reduced state, commonly thought o be the Sn ~ § oxidation state. Except for this minor prob-lem, the t in-act ivated phosphates are easily pre-pared and a wealth of new phosphors may be ob