Upconversion (UC)/downconversion (DC)-luminescent lanthanide-doped
nanocrystals (LDNCs) with near-infrared (NIR, 650–1700 nm)
excitation have been gaining increasing popularity in bioimaging.
However, conventional NIR-excited LDNCs cannot be degraded and eliminated
eventually in vivo owing to intrinsic “rigid”
lattices, thus constraining clinical applications. A biodegradability-tunable
heterogeneous core–shell–shell luminescent LDNC of Na3HfF7:Yb,Er@Na3ZrF7:Yb,Er@CaF2:Yb,Zr (abbreviated as HZC) was developed and modified with
oxidized sodium alginate (OSA) for multimode bioimaging. The dynamic
“soft” lattice-Na3Hf(Zr)F7 host
and the varying Zr4+ doping content in the outmoster CaF2 shell endowed HZC with tunable degradability. Through elaborated
core–shell–shell coating, Yb3+/Er3+-coupled UC red and green and DC second near-infrared (NIR-II) emissions
were, respectively, enhanced by 31.23-, 150.60-, and 19.42-fold when
compared with core nanocrystals. HZC generated computed tomography
(CT) imaging contrast effects, thus enabling NIR-II/CT/UC trimodal
imaging. OSA modification not only ensured the exemplary biocompatibility
of HZC but also enabled tumor-specific diagnosis. The findings would
benefit the clinical imaging translation of LDNCs.