Fig. 3
From: Upconversion amplification through dielectric superlensing modulation
Mechanistic investigations of dielectric superlensing-mediated upconversion amplification. a Upconversion fluorescence power-dependent studies of luminescence enhancement in the NaGdF4:Yb/Tm@NaGdF4:Eu-embedded PDMS substrate, recorded with and without microbead coverage. Error bars represent ± 1 s.d. b Proposed energy transfer diagrams showing the multistep excited state pumping of NaGdF4:Yb/Tm@NaGdF4:Eu UCNPs. The emission of Eu3+ is generated by accepting the down-shifting energy from Gd3+ sublattice. c Numerical simulation results based on a simplified energy transfer model involving two-to-five-photon upconversion processes. It is clear to find that upconversion emission from higher excited states is more sensitive to the excitation pumping rate. Besides, the luminescence enhancement dominates with higher-order upconversion emission. d Comparative simulations of the far-field emission collection efficiency for upconversion enhancement, obtained in the presence or absence of a dielectric microbead. e Down-shifting luminescence enhancement of Nd/Yb codoped NaYF4 nanocrystals using dielectric microbeads. (Inset) The proposed energy transfer mechanism for NaYF4:Nd/Yb down-shifting nanocrystals. Error bars represent ± 1 s.d. f, g Microbead-mediated enhancement recorded for linear and two-photon absorption luminescence from Rhodamine B dye molecules. (Insets) The corresponding Stokes emission and two-photon absorption-emission mechanisms, respectively. Error bars represent ± 1 s.d
