Fig. 1. The synthetic route of [Ru(bpy)₂Phen](ClO₄)₂

Fig. 2. The synthetic routes of DTACl and DTACN

Fig. 3. Normalized absorption and emission spectra of [Ru(bpy)₂Phen]²⁺ (a), DTACl (b) and DTACN (c) in DMF (1× 10^-6 mol·L^-1)

Fig. 4. Dependence of upconversion intensity on the relative concentrations of the emitters DTACl(a), DTACN (b)upon excitation at 488 nm with a power density of 9.92 mW·cm^-2; Upconversion and emission intensity of [Ru(bpy)₂Phen]²⁺ dependent on the concentration of emitters (b, d)

Fig. 5. Stern-Volmer analyses of [Ru(bpy)₂Phen]²⁺ quenched by the emitters

Fig. 6. The power-dependent upconversion spectra of [Ru(bpy)₂Phen]²⁺/DTACl (a) and [Ru(bpy)₂Phen]²⁺/DTACN (b); Inset: the logarithmic plots of upconversion intensity versus power density