Stoichiometric crystals of Ca5false(PO4)3F and Ca5false(PO4)3normalCl were grown by slowly cooling solutions of the polycrystalline apatites in fused CaCl2 or CaF2 . While fluorapatite is hexagonal, optical and x‐ray observations indicate that Ca5false(PO4)3normalCl has a monoclinic P21/normalb space group. All crystals of this compound are highly twinned. At about 200 °C a transition to a hexagonal phase false(P63/normalmfalse) occurs. Loss of CaCl2 from the crystals leads to a stabilization of the hexagonal phase whereas at low concentrations F ion impurities have the opposite effect. Some previous observations on the luminescence of Ca5false(PO4)3−normalxfalse(MnO4)normalxnormalCl can now be understood in terms of the lower symmetry structure.

Zinc sulfide containing copper at random zinc sites was prepared by radioactive decay of Zn~< Measurements indicate that the isolated copper impurities do not contribute to luminescent emission. Using a covalent model of zinc sulfide, and recognizing the acceptor-donor nature of activators and coaetivators, association of these impurities is found and the luminescent center is identified as second or third nearest neighbor associated activator-coactivator pairs. The nearest neighbor pairs are transparent to 3650~ radiation and have many of the characteristics necessary to account for edge emission.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.7.158.43 Downloaded on 2014-12-07 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.7.158.43 Downloaded on 2014-12-07 to IP

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The cathodoluminescence intensity as a function of the accelerating potential was measured for a number of powdered ZnS:Cu phosphors, each of which had a thin nonluminescent ZnS coating of known thickness deposited upon every grain. The luminescence efficiency is dominated by the power loss of the electron beam in the nonluminescent coating. The efficiency-voltage curves were analyzed in terms of the electron power loss function proposed by Makhov. Very good agreement with the experimental results was achieved after correcting for the nonplanar surface of the phosphor particles and the intrinsic surface deexcitation.