Mechanoluminescence of Bi-Activated NaYGeO4 Polycrystals and 3D Printed Scaffolds in the NUV/Blue and NIR Spectral Range

Mechanoluminescent (ML) materials emit light when mechanically stimulated, serving as sensors and light sources in applications such as stress sensing, anti-counterfeiting, and biomechanical imaging. ML in the ultraviolet and near-infrared regions can trigger light-induced processes in living organisms, offering potential for photodynamic therapy and diagnostics. However, bismuth-doped materials with UV and NIR ML are rarely reported. Herein, a series of NUV/Blue and NIR ML phosphors, NaY_1-xBi_xGeO₄ (NYGOB_x) (0.0 ≤ x ≤ 4.0 mol%), with mechanically induced (impact and scratching) and NIR persistent photoluminescence (pPL) characteristics are developed using a conventional solid-state reaction method. XPS and photoluminescence (PL) characterizations indicate the coexistence of bismuth in multiple valence states. The optimal NYGOBi_1.5 sample exhibits broadband UV/blue emission (325–525 nm, centered at 405 nm, PLQY of 45.70%, and FWHM of 63.70 nm), along with broadband NIR emission (900–1600 nm). The combination of NUV/blue (∼415 nm), NIR-I (∼825 nm), and NIR-II (∼1235 nm) pPL from Bi³⁺, Bi²⁺, and Bi⁺, respectively, is observed, with the durations of up to ∼100 s. A scratch-induced ML is visualized on a 3D-printed ML scaffold prepared using stereolithography (SLA) 3D printing technology, suggesting its potential application for functional lighting devices.