Fig. 1.

Orthogonal excitation superballs with mixed UCNPs A and B. TEM images of UCNPs A (a) and UCNPs B (b). 808 nm (c) laser and 980 nm laser (d) excited upconversion emission spectra of cyclohexane solutions at room temperature (25 °C) comprising A (red line) and B (black line) with same concentration. e TEM images of OP-SBs. f Schematic illustration of OP-SBs with luminescent photos taken by smart phone camera. g Normalized 808 nm laser (left) and 980 nm laser (right) excited upconversion emission spectra of superball aqueous suspension at room temperature (25 °C) with different mixing ratio between A and B. 808 and 980 nm laser power (1 W) are kept same throughout the measurement. h 808 nm laser (left) and 980 nm laser (right) excited upconversion emission spectra with increasing laser power of superball (A:B = 1:1) aqueous suspension at room temperature (25 °C). i Smartphone images of OP-SBs (A:B = 1:1) pattern under different 980 nm:808 nm laser power ratio. Scale bar: 50 nm for a, b, 200 nm for e. UCNPs A, NaYF₄: 60%Yb, 20%Gd, 2%Er@NaLuF₄: 25%Y; UCNPs B, NaYF₄: 30Yb, 0.5%Tm@NaYF₄: 10%Yb@NaNdF₄: 10%Yb