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

Abstract Multicolor photoluminescent Bi_0.4Ln_0.1Na_0.5Ta₂O₇²⁻ nanosheets (Ln = Eu, Tb, Dy, Sm, La) are prepared by delaminating an Aurivillius‐phase layered perovskite, Bi_2.4Ln_0.1Na_0.5Ta₂O₉. Both Bi³⁺ and Ln³⁺ (except La³⁺) successfully function as luminescent centers under UV‐light illumination (λ_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 Ln³⁺ or to Bi³⁺ is different in acidic or in basic solutions. Freestanding Bi_0.4Ln_0.1Na_0.5Ta₂O₇²⁻ 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⁺ (6s²–6s6p) and Ln³⁺ (4fⁿ–4fⁿ) influence the responsiveness to changes in the environment surrounding those luminescent centers.