Fig xA Rietveld refinement plot of neutron diffraction
These structural studies were done to gain insight about the effect that annealing in a reducing Erteberel has on the structure of Sr3AlO4F materials. It is apparent that the reducing atmosphere has a significant impact on the self-activated photoluminescence in Sr3AlO4F, resulting in a bright white light emission when excited by 254 nm light. Structurally this is concomitant with a significant contraction of the a lattice parameter and a minute elongation of the c axis. Within the Sr3AlO4F structure the FSr6 octahedrons reveal small distortions, commensurate with the expansion of the c lattice parameter. The contraction of the a lattice parameter in Sr3AlO4F(r) is concommittant with a significant decrease of the separation between the FSr6 octahedrons and AlO4 tetrahedrons. The smaller isotropic displacement parameter for Sr(1) and O indicates that the denser packing of the polyhedral units results in a slightly deeper potential for the Sr(1) and O atoms in this material. Both the air- and reductively-annealed samples have identical thermal expansion within the temperature range of 3–350 K. The Debye temperatures were calculated using the atomic displacement parameters and show no significant differences between the samples making the Debye temperature a bad proxy for self-activated PL. We have no model for the intense self-activated photoluminescence in the reduced materials only the experimental observation of densification and minute changes in the atomic displacement parameters of an under-bonded Sr(1) atom and oxygen liking the two polyhedral subunits.