Temperature sensors based on europium polyoxometalate and mesoporous terbium metal–organic framework

Abstract

The first example of ratiometric luminescent thermometers based on lanthanide molecular species encapsulated in a lanthanide metal–organic framework (MOF) is reported. In EuW₁₀@Tb-TATB, the [EuW₁₀O₃₆]⁹⁻ polyoxometalate (POM) is incorporated into the cavities of the mesoporous terbium MOF Tb-TATB with two different POM loadings (9.1 and 19.5 wt%). Eu³⁺ and Tb³⁺ ions of the POM and MOF, respectively, act as dual emitters. Optical measurements evidence efficient Tb³⁺-to-Eu³⁺ energy transfer, suggesting that the EuW₁₀ units are close to terbium centers. These observations are supported by computational investigations whereby a favored localisation of the EuW₁₀ POM in the MOF's pores is found close to Tb-centers evidencing hydrogen bond type interactions between terminal oxygen atoms of the POM and Tb-coordinated water molecules. The reported materials act as temperature sensors in the physiological domain, exhibiting high relative thermal sensitivities of 2.68% K⁻¹ and 2.37% K⁻¹ at 300 K for the 9.1 wt% and 19.5 wt% composites, respectively, with a thermal uncertainty of 0.09 K.