Fig. 2: Red/green color-switchable upconversion in Er/Tm/Yb tri-doped nanoparticles.
From: Full-color tuning in multi-layer core-shell nanoparticles from single-wavelength excitation
a Upconversion emission spectra of NaYF4:Er/Tm/Yb(15/0.5/40 mol%)@NaYF4 and NaYF4:Er/Yb(15/40 mol%)@NaYF4 core-shell nanoparticles under 980 nm excitation. b, c Upconversion emission intensity ratio of green emission (γ) over the total emissions obtained from the NaYF4:Yb/Er/Tm(40/10-40/0.5 mol%)@NaYF4 and NaYF4:Yb/Er/Tm(0-60/15/0.5 mol%)@NaYF4 core-shell nanoparticles under c.w. and pulse excitations. d Normalized upconversion emission spectra of NaYF4:Yb/Er/Tm(40/15/0.5 mol%)@NaYF4 core-shell nanoparticles under c.w. and pulse 980 nm excitations. e CIE (x,y) chromaticity diagram of emission colors of sample in (d). Insets show the corresponding emission photographs. f Time-dependent upconversion emission profiles of Er3+ at 540 and 654 nm for (d) sample. g Time-dependent upconversion emission profiles of Er3+ at 540 nm from NaYF4:Er(15 mol%)@NaYF4, NaYF4:Er/Yb(15/40 mol%)@NaYF4 and NaYF4:Er/Tm(15/0.5 mol%)@NaYF4 core–shell nanoparticles (top panel) and that of Er3+ at 540 nm from NaYF4:Er/Yb/Tm(15/40/0.5 mol%)@NaYF4 core-shell nanoparticles and Tm3+ at 695 and 800 nm from NaYF4:Yb/Tm(40/0.5 mol%)@NaYF4 core-shell nanoparticles (bottom panel). h Decay curves of Er3+ at its 4S3/2 state (540 nm) from NaYF4:Er(15 mol%)@NaYF4, NaYF4:Er/Tm(15/0.5 mol%)@NaYF4 and NaYF4:Er/Tm/Yb(15/0.5/40 mol%)@NaYF4 samples under pulse 980 nm excitation. i Infrared emission spectra of NaYF4:Er/Tm(15/0.5 mol%)@NaYF4 and NaYF4:Er/Tm/Yb(15/0.5/40 mol%)@NaYF4 samples under 980 nm excitation. j Schematic of possible processes for the observation of green emission color under short pulse laser excitation. CR1 and CR2 stand for [Er3+ (2H11/2); Tm3+ (3F4)] → [Er3+ (4I9/2); Tm3+ (3H4)] and [Er3+ (2H11/2); Tm3+ (3F4)] → [Er3+ (4I11/2); Tm3+ (3F2,3)], respectively.
