A research group led by Prof.CHANG Yulei from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) proposed a strategy of enhancing the interaction of highly doped Tm³⁺ ions through nanostructure design to achieve efficient NIR-IIc fluorescence emission. The study was published in Nature Communications.

Fluorescence imaging has broad application prospects in biomedical imaging and diagnosis. Short wave infrared (1000-3000 nm), also called NIR-II, has been widely used in wide-field and microscopic imaging of living organisms due to its lower absorption and scattering of photons and deeper tissue penetration compared to UV-Vis and NIR-I.

Utilizing the rich energy level structure of rare earth-doped nanomaterials (RENPs), diverse emission bands, narrow emission peaks, large (anti) Stokes shifts, stable photochemical properties, and ease of surface functional modification, it has become an ideal NIR-II imaging probe. Therefore, constructing a RENPs-based NIR-II fluorescence probe is of great significance.

This work enhanced the cross-relaxation process between Tm³⁺ to enhance the ³F₄ → ³H₆ energy level transition and uses an epitaxial optical inert shell to effectively avoid the surface quenching, resulting in ~1800 nm emission and achieving efficient NIR-II quantum efficiency (QY=~14%). Further, they optimized the NIR-II luminescence brightness by doping a small amount of Er³⁺(<0.5%). If the concentration of Er³⁺ was further increased to 30%, these "alloy" nanoparticles could respond to excitation at four wavelengths (800 nm, 980 nm, 1208 nm, and 1530 nm), providing a powerful research tool for secure optical coding and in vivo imaging.

The study has initially achieved imaging application results, but it is still necessary to further improve the luminous efficiency of the probe and increase channels of excitation and emission to meet the needs of multi-channel imaging and multi-target detection. This research has broadened the direction of progress in fields such as biomedicine and medical diagnosis.