Multi-stimulated far-UVC luminescence for solar-blind imaging

Lanthanides-doped luminescent materials have gathered considerable attention due to their application potential in stress sensing, lighting and display, anti-counterfeiting technology and so forth. However, existing materials mainly cover the 380–1540 nm range, with slight extension to the UV region, impeding their applications in solar-blind imaging, background-free tracking, concealed communication, etc. To address this challenge, here we propose guidelines for far-UVC (200–230 nm) optical design. Accordingly, we achieve multi-stimulated far-UVC luminescence at ~222 nm in Pr 3+ -doped SrF 2 , stemming from the inter-configurational 4f5d → 4f  2 transition of Pr 3+ . Besides Pr 3+ , the SrF 2 host shows high tolerance to Ce 3+ , Nd 3+ , Sm 3+ , Eu 2+,3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ , vastly extending the emission wavelength across the entire spectral range from 200 to 1700 nm. Particularly, these materials exhibit self-recoverable mechanoluminescence by direct mechanical excitation, along with thermally and mechanically stimulated emission after X-ray irradiation. We demonstrate that these lanthanides-doped SrF 2 crystals offer unique opportunities for high-contrast marking and structural health monitoring in complex environments.