Lattice site dependent cathodoluminescence behavior and surface chemical changes in a Sr ₅(PO ₄) ₃F host

Eu activated Sr ₅(PO ₄) ₃F phosphor powders have been subjected to the electron bombardment at 2 keV (10 μA) at an oxygen pressure of 1×10 ^-6 Torr. The synthesized Sr ₅(PO ₄) ₃F phosphor was identical to the hexagonal apatite structure, with the Sr present at two different sites C _s (S1) and C ₃ (S2) in the Sr ₅(PO ₄) ₃F host, as inferred from the crystallographic study. Cathodoluminescence (CL) and Auger electron spectroscopy of the phosphor excited by the same electron beam were used to monitor changes in the surface state during prolonged electron bombardment. A direct correlation between the surface reactions and the degradation of the CL brightness was observed. Both C and F were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated chemical reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species, which subsequently react with C to form volatile compounds CO ₂, CH ₄, etc. and with Sr ₅(PO ₄) ₃F to form a non luminescence layer of metal oxides of Sr and P.