Plaque brightness depreciation of Ca10F2(PO4)6:Sb, Mn phosphors subjected to 185 nm radiation in a nitrogen atmosphere is found to be approximately an inverse linear function of Sb concentration and to be independent of Mn content. When irradiation is carried out in the prescence of as little as 0.2% O2, depreciation of phosphors containing Mn may be much greater than in a pure N2ambient. This appears to be caused by photo-oxidation of Mn on or close to the surface of the phosphor crystal. The results of magnetic susceptibility measurements rule out the likelihood that photo-oxidation of Mn, when it occurs, involves either a redox couple with an electron acceptor in the structure or residual oxygen adhering to the surface. It is shown that both the Sb and Mn emission intensities are reduced in the same proportion following exposure to 185 nm radiation, so that loss of luminous efficiency is probably the result of dissipation of excitation energy prior to absorption by Sb and/or a non-radiative process occurring after absorption by Sb. From diffuse reflectance spectra the following radiation-induced absorptions associated with the presence of Sb are found: two unresolved peaks at 320 and 350 nm and absorption at 254 nm. The relative absorption in each of these regions increases with increasing depreciation. © 1974.
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