Site-selective emission spectra of Eu3+: Ca-5(PO4)(3)F

The room temperature site-selective fluorescence and excitation spectra of Eu3+:FAP powder samples as well as the decay times of the observed emission lines associated with the D-5(0) --> F-7(0,1,2) transitions have been meas ured. In sample I, prepared by the thermally stimulated diffusion of Eu2O3 in the solid state, Eu3+ reside only in the Ca(II) location which has C-s s ymmetry. Experimental values for the Stark energy levels have been determin ed for three well-separated sites. Sites A and B exhibit very similar spect ral features attributed to the presence of the charge-compensating O2- ion in the F- position in the FAP lattice, whereas for Eu3+ in site C the charg e is most probably compensated by vacancies according to 3Ca(2+) --> 2Eu(3) +Vacancy substitution. In sample II, prepared by precipitation of Eu3+(1% ):FAP from solution, Eu3+ substitute for calcium in the Ca(I) position excl usively and three sites with C-3 symmetry have been identified. Substitutio n of 3Ca(2+)/2Eu(3+) is the most probable charge-compensation mechanism. He ating of sample II stimulates the migration of Eu3+ from the Ca(I) position to the low symmetry Ca(II) site. (C) 2000 Elsevier Science S.A. All rights reserved.