Intervalence charge transfer of Cr(3+)-Cr(3+) aggregation for NIR-II luminescence

The increasing demand for high-contrast biological imaging, non-destructive testing, and infrared night vision can be addressed by the development of high-performance NIR light-emitting materials. Unlike lanthanide (Ln(3+)) with sharp-line multiplets and isolated Cr(3+) with NIR-I emission, this study reports the first-ever NIR-II broadband luminescence based on the intervalence charge transfer (IVCT) of Cr(3+)-Cr(3+) aggregation in gallate magentoplumbite. In particular, LaMgGa(11)O(19):0.7Cr(3+) exhibits dual-emission (NIR-I, 890 nm and NIR-II, 1200 nm) with a full width at half maximum (FWHM) of 626 nm under 450 nm blue LED excitation. Moreover, this dual-emission exhibits anti-thermal quenching behavior (432% @ 290 K), attributed to the energy transfer among multiple Cr(3+) centers. Cryogen absorption spectra, lifetimes decay (2.3 ms), and electron paramagnetic experiments reveal the NIR-II luminescence of the Cr(3+)-Cr(3+) → Cr(2+)-Cr(4+) IVCT transition. The application of LaMgGa(11)O(19):0.7Cr(3+) in NIR-II biological imaging as an optical contrast agent, non-destructive testing, and night vision is demonstrated. This work provides new insights into broadband NIR-II luminescence under UV-NIR excitation based on the IVCT of Cr(3+)-Cr(3+) aggregation.