Stress-Induced Photoluminescence Change of Monolayer Nanosheet Prepared by Delamination of Aurivillius-Phase Layered Perovskite

A comprehensive investigation was performed on the photoluminescence properties of monolayer Bi3+-substituted ATa2O72– (A = Ca, Sr, Bi0.5Na0.5). The Bi3+ center in the A–Ta–O perovskite framework functioned as a luminescence center (λmax = 470–520 nm) under UV-light illumination (λex = 250–340 nm). Comparison of the photoluminescence spectra of Bi3+ in several types of layered ATa2O72– structures, including Bi2ATa2O9 ((Bi2O2)(ATa2O7)), protonated Bi2ATa2O9 (H2ATa2O7·xH2O), and free-standing ATa2O72– nanosheet membranes, revealed that the positions of the emission and excitation bands were greatly influenced by the interlayer cation species. The results implied that the photoluminescence properties of Bi3+ in ATa2O72– were sensitive to changes in the electric field surrounding Bi3+ because of the ultimate thinness of the monolayer ATa2O72– nanosheets (1.1–1.2 nm). To further explore the relationship between mechanical stress in Bi3+-substituted ATa2O72– nanosheets and the emission band of Bi3+, changes in the photoluminescence and Raman spectra in response to the curvature radius of free-standing ATa2O72– nanosheet membranes were compared. The present study confirmed that two-dimensional nanomaterials could help further the understanding of mechanochromic phenomena in Bi-containing inorganic materials.