Grafting of a Eu3+-tfac complex on to a Tb3+-metal organic framework for use as a ratiometric thermometer

Abstract

Microrods of [Tb₂(bpydc)₃(H₂O)₃]·nDMF (TbMOF) were employed as a platform for grafting a β-diketonate complex of Eu³⁺ for the purpose of obtaining ratiometric luminescence thermometer materials. A straightforward post-synthetic functionalization is employed to obtain the TbMOF@Eu_tfac (tfac = trifluoroacetylacetonate) compounds. The emission color of the TbMOF@Eu compounds can be slightly tuned by varying the percentage of the grafted β-diketonate complex of Eu³⁺. Also, as shown, the thermometric properties of the material can be tuned by the percentage of grafted β-diketonate complex of Eu³⁺. The TbMOF@3%Eu_tfac and TbMOF@7.3%Eu_tfac compounds were investigated in detail for their use as luminescent ratiometric thermometers. For the TbMOF@3%Eu_tfac compound an absolute sensitivity S_a of 0.069 K⁻¹ (225 K) and relative sensitivity S_r of 2.59%K⁻¹ (225 K) were obtained showing its good sensing capability. For the TbMOF@7.3%Eu_tfac compound a S_a of 0.012 K⁻¹ (275 K) and relative sensitivity S_r of 1.33%K⁻¹ (325 K) were obtained showing that the TbMOF@3%Eu_tfac compound is superior for temperature sensor applications. We also show that the emission color of the parent TbMOF material itself can be tuned by varying the excitation wavelength from 250–380 nm. It can be tuned from light-green to blue by simply changing the excitation wavelength.