Studying crystal-field splitting difference of Eu3+ ions from orthorhombic to cubic Ca4Al6SO16

Abstract

Eu3+ lanthanide ion possesses abundant 4f-4f transition lines in the visible spectral region, and its spectroscopic changes can sensitively reflect the variation of local ligand environments. Here, Eu3+ ions are successfully introduced into Ca4Al6SO16 lattice, and the structural difference from orthorhombic (o-Ca4Al6SO16) to cubic (c-Ca4Al6SO16) phases is systematically analyzed. On that basis, the related influence on crystal-field splitting of Eu3+ ions is discussed in detail. The obtained results indicate that Eu:o-Ca4Al6SO16 and Eu:c-Ca4Al6SO16 have three and two non-degenerate 5D0→7F0 transition peaks, respectively. Through the theoretical analysis and low-temperature (78 K) luminescent investigation with changing the excitation wavelength, those non-equivalent Ca2+ sites are assigned as o-Ca(1) (~577.6 nm), o-Ca(3) (~579.6 nm), o-Ca(4) (~580.6 nm), c-Ca(1) (~578.7 nm), and c-Ca(2) (~580.2 nm), respectively. In addition, with the increase of c-Ca4Al6SO16 content in the sintered product, the fluorescence intensity ratios of I580.6/I613.7, I616.2/I613.7 and I621/I613.7 present a gradual decreasing tendency. And, the introduction of c-Ca4Al6SO16 into the as-prepared product is beneficial for increasing the decay lifetime of the 5D0 excited state and enhancing the resistance capability to thermally induced fluorescence quenching. What discussed in this work might provide some useful thoughts for multi-phase studies and broaden the application range of lanthanide fluorescent probes.