Fig. 2

Experimental investigations on upconversion luminescence amplification through dielectric superlensing. a Upconversion emission spectra of NaYF₄:Yb/Er@NaYF₄ and NaGdF₄:Yb/Tm@NaGdF₄:Eu core-shell nanoparticles recorded under 980 nm laser excitation (~20 W cm⁻²). (Inset) Corresponding photos of the nanoparticles dispersed in cyclohexane upon 980 nm excitation. b Schematic illustration of the experimental setup designed for luminescence amplification investigation. The as-prepared UCNPs are embedded in a PDMS precusor and then spin-coated on a glass substrate to form the upconverting film. The dielectric superlensing monolayer was prepared by adding polymeric microbeads on the top of the upconverting film. A ×10 objective lens was used to guide the 980 nm excitation light onto the film and simultaneously collect the upconversion emission. c Upconversion luminescence images of the UCNP-embedded PDMS upconverting films recorded with and without the microbead coverage upon 980 nm laser excitation at different intensities. d Power-dependent investigations of microbead monolayer induced-luminescence enhancement for PDMS films comprising NaYF₄:Yb/Er@NaYF₄ and NaGdF₄:Yb/Tm@NaGdF₄:Eu nanoparticles. Error bars represent ± 1 s.d