A ratiometric fluorescent pH sensor based on nanoscale metal-organic frameworks (MOFs) modified by europium(III) complexes.

We report a new ratiometric fluorescent pH sensor based on postsynthetically modified nanoscale MOF-253. Two types of Eu(3+) with different characteristic excitation wavelength are realized in MOF-253 by a postsynthetic method (PSM). The pH sensor requires no calibration because only one of the two types of Eu(3+) is affected by the pH variation.