Ultra-wideband-responsive photon conversion through co-sensitization in lanthanide nanocrystals.

Distinctive upconversion or downshifting of lanthanide nanocrystals holds promise for biomedical and photonic applications. However, either process requires high-energy lasers at discrete wavelengths for excitation. Here we demonstrate that co-sensitization can break this limitation with ultrawide excitation bands. We achieve co-sensitization by employing Nd and Ho as the co-sensitizers with complementary absorptions from the ultraviolet to infrared region. Symmetric penta-layer core-shell nanostructure enables tunable fluorescence in the visible and the second near-infrared window when incorporating different activators (Er, Ho, Pr, and Tm). Transient spectra confirm the directional energy transfer from sensitizers to activators through the bridge of Yb. 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. This co-sensitization strategy paves a new way in lanthanide nanocrystals for multidirectional photon conversion manipulation and excitation-bandwidth-regulated fluorescence applications.