Optimising FRET-efficiency of Nd3+-sensitised upconversion nanocomposites by shortening the emitter–photosensitizer distance

Nanocomposite NaYF₄:Nd,Yb@Yb@Yb,Er@Y with Nd³⁺ in the core and Er³⁺ in the shell to shorten the emitter (Er³⁺)–photosensitizer distance to achieve better Förster resonance energy transfer (FRET) for better-performing photo-nanotheranostic materials.