Tunable Photoluminescence of Bismuth- and Trivalent-Lanthanide-Doped Monolayer Perovskite Oxide Nanosheets

Multicolor photoluminescent Bi(0.4)Ln(0.1)Na(0.5)Ta(2)O(7)(2-) nanosheets (Ln = Eu, Tb, Dy, Sm, La) are prepared by delaminating an Aurivillius-phase layered perovskite, Bi(2.4)Ln(0.1)Na(0.5)Ta(2)O(9). Both Bi3+ and Ln(3+) (except La3+) successfully function as luminescent centers under UV-light illumination (& lambda;(ex.) = 240-340 nm), which result in a photoluminescence color that can be tuned by changing the lanthanide doping. The emission spectra are influenced by pH because the energy distribution to Ln(3+) or to Bi3+ is different in acidic or in basic solutions. Freestanding Bi(0.4)Ln(0.1)Na(0.5)Ta(2)O(7)(2-) nanosheet membranes are prepared by vacuum filtration, and the relationship between the photoluminescence and structural properties of the nanosheet membranes is investigated. The results indicate that differences in the electron orbitals involved in the photoluminescence of Bi3+ (6s(2)-6s6p) and Ln(3+) (4f(n)-4f(n)) influence the responsiveness to changes in the environment surrounding those luminescent centers.