Distinct structural and optical correlations of Y1−xEuxOF and Yn(1−x)EunxOn−1Fn+2 (x=0.001-0.1, n=6, 7) vernier phosphors

Eu3+ substituted YOF and vernier-phase YnOn−1Fn+2 (n=6, 7) phosphors, which are rhombohedral and orthorhombic structures, respectively, were prepared using a flux-assisted reaction at different temperatures. Stoichiometric and nonstoichiometric yttrium oxyfluoride phases were identified by examination of the indexed peak positions in the X-ray diffraction patterns of the resultant phosphors; however, Y6O5F8 and Y7O6F9 lattice structures in vernier phases were indistinguishable by this method. To identify the vernier phases, the photoluminescence excitation and emission spectra peaks assigned to charge-transfer bands and f-f transitions of Eu3+ ions in YnOn−1Fn+2 host with the YOF were monitored. The YnOn−1Fn+2 vernier phases were indicated by the O2−(F−)-Eu3+ charge-transfer bands and the site symmetry of Eu3+ emission assigned by 5D0→7F1, 7F2 transitions, and were classified as centrosymmetric Y6O5F8 and noncentrosymmetic Y7O6F9 structures. The critical distances (Rc) in both Y1−xEuxOF and Y6(1−x)Eu6xO5F8 (x=0.001-0.1) lattice structures were calculated by observation of quenching of the relative intensity in the Eu3+ activated red emission.