“…[22] These complexes are widely applied as labels in various luminescence assays both as free dyes bearing a functional group for conjugation and in the form of dye-doped nanoparticles, [22,23] but application in optical sensors and analyte-sensitive probes is comparably rare. [24][25][26][27] For example, luminescent Eu(III) complexes were applied as optical temperature probes, [27][28][29][30][31] pH indicators, [32][33][34][35][36] fluoroionophores for bicarbonate, [37,38] citrate [39] and lactate [40] and as hydrogen peroxide [41] and nitrogen monooxide probes. [42] Several Eu(III) complexes were applied as luminescent oxygen indicators.…”