Highly chemical and thermally stable luminescent EuxTb1−x MOF materials for broad-range pH and temperature sensors

Abstract

New luminescent Ln-MOFs, [Ln₂(D-cam)(Himdc)₂(H₂O)₂] (Ln = Eu 1, Tb 2, D-H₂cam = D-camphoric acid, H₃imdc = 4,5-imidazole dicarboxylic acid) have been synthesized via hydro(solvo)thermal reactions. X-ray single crystal structure analysis reveals that they are isomorphic and both crystallize in the orthorhombic space group Pna2₁. Compound 1 shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13 and is highly stable in several boiling solvents, which make it potentially useful for wide-range pH sensors, especially in the physiological environment with pH = 6.8–8.0. Careful adjusting of the codoping ratio of Eu³⁺/Tb³⁺ into the same framework of 1 affords a mixed Ln-MOF, formulated as [Eu_0.7Tb_0.3(D-cam)(Himdc)₂(H₂O)₂]₃, which has demonstrated to be a viable probe for sensing temperature in a wide temperature range from 100 to 450 K.