Cryogenic luminescent thermometers based on multinuclear Eu³⁺/Tb³⁺ mixed lanthanide polyoxometalates

Here, the excellent thermal sensing capability of a multinuclear lanthanide polyoxometalate in the cryogenic region (<100 K) is presented for the first time. Up till now, no lanthanide polyoxometalates have been studied for their use as ratiometric luminescent thermometers. The investigated Tb³⁺ polyoxometalate cluster is doped with 1.6% (P1) and 8.4% (P2) of Eu³⁺ ions. When excited into the Mo-O charge transfer bands, at room temperature only the emission of the Eu³⁺ ions is observed suggesting a very efficient energy transfer between Mo-O→Tb³⁺→Eu³⁺. Only in the cryogenic region the emission of Tb³⁺ is also witnessed.