Fig. 3: Spatial control of upconversion.
From: Spatiotemporal control of photochromic upconversion through interfacial energy transfer
a Normalized upconversion emission intensity of NaErF4:Ho(0.5 mol%)@NaYF4:Yb(0–100 mol%)@NaYF4 core-shell-shell nanoparticles with variable Yb3+ concentrations. The absorption intensity was also plotted for comparison. The data were normalized to the sample with 0 mol% Yb3+ content. b Absorption spectra of (a) samples due to Yb3+ (2F5/2 ← 2F7/2 transition) and Er3+ (4I11/2 ← 4I15/2 transition). c Upconversion emission spectra of NaErF4:Ho(0.5 mol%)@NaYF4@NaYbF4@NaYF4 samples with a fine tuning of the NaYF4 interlayer thickness from 0 to 8.7 nm. d A comparison of emission intensity of c samples normalized to that without the NaYF4 interlayer. e A comparison of upconversion emission intensity from (c) sample with 2.1 nm thick NaYbF4 interlayer (ErHo@Y@Yb@Y) and control NaYF4:Yb/Er(20/2 mol)@NaYF4 core-shell nanoparticles (YbEr@Y) under identical measurement condition. f Dependence of energy transfer rate between Yb3+ and Er3+ on the ionic distance. WET and Ar represent energy transfer rate and spontaneous emission rate, respectively. All excitation power densities were 11.6 W cm‒2. Source data are provided as a Source Data file.
