Scheme 1

Schematic illustrations of NIR energy shifting process in water. a Water-insensitive NIR-I-to-NIR-I down-shifting nanoparticle (WINPs, NaYF₄:Nd@NaYF₄) and b conventional 980-to-NIR-I up-conversion nanoparticle (UCNPs, NaYF₄:Yb,Tm@NaYF₄)