Fig. 6: Sensing experiment of acid and alkali solutions.

R-Eu-Et-1 to C(H+) = 0.001 M (pH = 3) (A) and C(OH−) = 0.01 M (pH = 12) (B) concentration-dependent PL spectra under excitation at 365 nm and fitting curves of aqueous solutions (C). E, F R-Eu-Et-2 to C(H+) = 0.001 M (D) and C(OH−) = 0.01 M (E) concentration-dependent PL spectra under excitation at 365 nm and fitting curves of aqueous solutions (F). G Comparison of the pH ranges of R-Eu-Et-1/2 and different types of pH sensors that have been reported. Note: Dark blue shading represents a series of metal-organic frameworks; orange shading represents quantum dots; green shading represents a series of nanoparticles; yellow shading represents small molecules; light blue shading represents this work.