Figure 4

Possibility of modulating the blue/green UC fluorescence emission from the Tm³⁺ (a,b) and Er³⁺ (c,d) single-doped GCs. Setting the excitation power of one NIR laser to a fixed value while increasing the power of another NIR laser, a I_TSTW/(I_SW1+I_SW2) fluorescence increase is observed (Where I_TSTW, I_SW1 and I_SW2 represent the blue/green UC fluorescence intensities generated by two-step excitation of two-wavelengths, and by single-wavelength excitation. For Tm³⁺, I_TSTW denotes I₁₊₈ in (a) and I₈₊₁ in (b) upon two-step excitation of 1064 and 800 nm, I_SW1 illustrates I₁ in (a) and (b) upon single 1064 nm excitation, and I_SW2 illustrates I₈ in (a) and (b) upon single 800 nm excitation, respectively. For Er³⁺, I_TSTW denotes I₈₊₁ in (c) and I₁₊₈ in (d) two-step excitation of 850 and 1530 nm, I_SW1 illustrates I₁ in (c) and (d) upon single 1530 nm excitation, and I_SW2 illustrates I₈ in (c) and (d) upon single 850 nm excitation, respectively.), which is nonlinear when the NIR laser power increases⁴³. The arrows represent the maximum tailorable UC fluorescence efficiency.