Fig. 2: Characterization and upconversion emission spectra.
From: Spatiotemporal control of photochromic upconversion through interfacial energy transfer
a TEM image, high resolution TEM image (right top panel) and the corresponding Fourier transform diffraction pattern (right bottom panel) of the as-synthesized NaErF4:Ho(0.5 mol%)@NaYF4:Yb(20 mol%)@NaYF4 core-shell-shell nanoparticles. b STEM image of (a) sample and corresponding elemental mappings of Er, Yb, Y and F. c Upconversion emission spectra of NaErF4:Ho(0.5 mol%)@NaYF4:Yb(0–100 mol%)@NaYF4 core-shell-shell nanoparticles with a fine tuning of Yb3+ dopant concentration in the sensitizing layer under 980 nm excitation. d Dependence of normalized upconversion emission intensity on Yb3+ dopant concentration of (c) sample under 808, 980 and 1530 nm excitations, respectively. The data were normalized to the red emission intensity of (c) sample without Yb3+ doping. e Dependence of slope values of upconversion emissions on Yb3+ concentration for (c) samples under 980 nm excitation. Inset shows possible cross relaxations to populate the 4F9/2 state of Er3+. f Upconversion emission spectra of NaErF4:Ho(0.5 mol%)@NaYbF4@NaYF4 core-shell-shell nanoparticles with a fine tuning of NaYbF4 layer thickness (0–7.5 nm) under 980 nm excitation. All excitation power densities were 11.6 W cm‒2. Source data are provided as a Source Data file.
