Fig. 11

NIR dye-sensitized modified upconversion nanoparticles: a, b Schematic illustrations of energy-cascaded upconversion in dye-sensitized core/shell nanocrystals (S1: type 1 sensitizer; S2: type 2 sensitizer; A: activator). Adapted with permission from Prasad et al.¹⁰⁰ (copyright 2015 American Chemical Society). c Schematic showing the proposed energy transfer mechanism for core/shell UCNs without (top) and with (bottom) Yb³⁺ doping. d Emission spectra of IR-806-sensitized core only (β-NaYF₄:20%Yb³⁺, 2%Er³⁺), core/NaYF₄ shell (β-NaYF₄:20%Yb³⁺,2%Er³⁺@β-NaYF₄), core/Yb³⁺ shell (β-NaYF₄:20%Yb³⁺, 2%Er³⁺@β-NaYF₄:10%Yb³⁺). e Excitation spectrum of β-NaYF₄:20%Yb³⁺, 2%Er³⁺@β-NaYF₄:10%Yb³⁺ (core/Yb³⁺ active shell) nanoparticle with (black squares) and without (red circles) IR-806 dye sensitization. Adapted with permission from Han et al.¹⁰⁴ (copyright 2016 American Chemical Society)