Site-Dependent Eu3+ Photoluminescence in Double Perovskite-Type Alkaline Earth Lanthanum Tantalates

ABSTRACT Site-dependent Eu3+ photoluminescence (PL) was examined utilizing the structural difference of two Eu3+ doped alkaline earth lanthanum tantalates with the B-site-ordered double perovskite-type structure (AA’)[BB’]O6, viz. (CaLa1−xEux)[CaTa]O6 (CLTO:Eu3+) and (Ba2)[La1−xEuxTa]O6 (BLTO:Eu3+) (x = 0.01, 0.10). The locations of the Eu3+ ions were experimentally determined by X-ray absorption near edge structure of the Eu LIII edge and confirmed to be A sites in CLTO:Eu3+ and B sites in BLTO:Eu3+ as expected from the nominal compositions. Intense charge transfer (CT) excitation bands were observed in the UV region in the PL excitation spectra of both materials. Because of the shorter bond lengths and larger electronic repulsion at B sites than A sites, the CT excitation band of Eu3+ at B sites in BLTO:Eu3+ was blue-shifted compared to that of Eu3+ at A sites in CLTO:Eu3+. By UV excitation in the CT bands, both materials showed red luminescence. However, due to the difference in the site symmetry of A and B sites, the Eu3+ emission was mainly derived from the 5D0 – 7F2 transitions in CLTO:Eu3+ and from the 5D0 – 7F1 transitions in BLTO:Eu3+ in relation with Eu3+ at A and B sites, respectively. The lifetimes of the emission were also dependent on the Eu3+ sites resulting in the longer lifetimes of Eu3+ ions at B sites than those at A sites.