Construction of Highly Luminescent Lanthanide Coordination Polymers and Their Visualization for Luminescence Sensing

NaH₂SIP was selected as an organic ligand (NaH₂SIP = 5-sulfoisophthalic acid monosodium salt). We successfully constructed a new class of lanthanide coordination polymers Ln-HS ([Ln(SIP)(DMF)(H₂O)₄]DMF·H₂O; Ln = Eu, Tb, Sm, and Dy) by a simple solvothermal synthesis method. They exhibited excellent photoluminescence properties for Ln³⁺ ions, where Eu-HS and Tb-HS exhibited high quantum yields of 13.70 and 42.38%, respectively. The codoped lanthanide coordination polymers obtained by doping with different ratios of Eu³⁺/Tb³⁺ serve as excellent ratiometric thermometers with high sensitivities in the physiological temperature range, with values of 16.8, 7.0, and 14.5%·K^-1, respectively. The luminescent colors of Tb_0.95Eu_0.05-HS and Tb_0.94Eu_0.06-HS exhibit variations from green to yellow to orange, achieving visualized luminescence in a narrow temperature range. The composite film material Tb_0.94Eu_0.06-HS@PMMA demonstrates this color variation. Next, Tb_0.5Sm_0.5-HS obtained by Tb³⁺/Sm³⁺ codoping was investigated. The difference in the luminescence colors visible to the naked eye at different excitation wavelengths and the change in luminescence colors occur in a very narrow temperature range. All of them show the great value of the visualized luminescence in practical anticounterfeiting, with double anticounterfeiting function and high security.