Site-selective spectroscopy of europium(III) exchanged bʺ-alumina

Crystals of 34% exchanged Eu$ sp{3+} beta sp{ prime prime}$-alumina were studied using site-selective spectroscopic techniques. The Eu$ sp{3+}$ ions were found to exhibit spectra which could be categorized into three types of emitting centres. These emitting centres are related to the crystallographic sites available for Eu$ sp{3+}$ in $ beta sp{ prime prime}$-alumina, namely the mid-Oxygen and Beevers-Ross sites. The fluorescent lifetimes were measured and were found to be consistent with the site assignments, particularly in the variations possible in the Eu$ sp{3+}$ coordination in mid-Oxygen sites. Analysis of the emission intensities reveals that the calculated site populations are in agreement with previously published X-ray results. Crystal-field analysis of the spectra indicates that the different types of centres are subject to different crystal-field strengths and that effects such as J-mixing play an important role in the observed spectra. Point-charge lattice sum calculations on an idealized structure of the $ beta sp{ prime prime}$-alumina crystal are in qualitative agreement with the crystal-field analysis and also provide a model for the observed inhomogeneous linewidths based on the number of residual sodium atoms in the unit cell. In addition, several anomalous features of the Eu$ sp{3+}$ spectra are described and discussed in terms of the structure of the crystal and its influence on the Eu$ sp{3+}$ ion's energy levels