Hence costly high-energy lasers at specific wavelengths, instead of cost-effective and readily available light sources, are required for the excitation of LnNCs. However, the intrinsic parity-forbidden 4f-4f electronic transition of Ln 3+ leads to ultralow molar extinction coefficients <10 cm −1 M −1 with linear absorption behaviors 11, 12. The abundant electronic energy levels of trivalent lanthanide ions (Ln 3+) offer the possibility for controllable regulation of photon conversion in an ultrawide range spanning from the ultraviolet (UV) to infrared 8, 9, 10. Smart control of photon conversion in lanthanide nanocrystals (LnNCs) is an important topic owing to its valuable scientific and technological implications on bioimaging 1, 2, 3, cancer treatment 4, 5, optical sensing 6, information storage and security 7, and so on. This co-sensitization strategy paves a new way in lanthanide nanocrystals for multidirectional photon conversion manipulation and excitation-bandwidth-regulated fluorescence applications. We validate the features of the nanocrystals for low-powered white light-emitting diode-mediated whole-body angiography of mice with a signal-to-noise ratio of 12.3 and excitation-regulated encryption. Transient spectra confirm the directional energy transfer from sensitizers to activators through the bridge of Yb 3+. Symmetric penta-layer core-shell nanostructure enables tunable fluorescence in the visible and the second near-infrared window when incorporating different activators (Er 3+, Ho 3+, Pr 3+, and Tm 3+). We achieve co-sensitization by employing Nd 3+ and Ho 3+ as the co-sensitizers with complementary absorptions from the ultraviolet to infrared region. Here we demonstrate that co-sensitization can break this limitation with ultrawide excitation bands. However, either process requires high-energy lasers at discrete wavelengths for excitation. Distinctive upconversion or downshifting of lanthanide nanocrystals holds promise for biomedical and photonic applications.
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