“…Recent studies have shown that, among lanthanide ions, Eu 3+ ions are the most prevalent in the development of new pH sensors having a MOF or a complex structure. 44,63,[65][66][67][68][69][70] As presented, these sensors can exhibit a wide usable pH range, covering 2-8, 66 1.05-9.85 67 and 1.06-10.99; 63 however, in this case, their sensing performance exploits a single emission intensity of Eu 3+ ions, which has been found to significantly reduce their reliability, especially when concerning biological applications. 36 From the sensing perspective, the ratiometric approach has been stated to be much more favorable in terms of highly sensitive and accurate pH measurements.…”