Europium beta-diketonate temperature sensors: Effects of ligands, matrix, and concentration

Europium beta diketonates are easily synthesized highly luminescent complexes with high temperature sensitivity. We report on the temperature dependence of the luminescence of recently synthesized europium complexes originally prepared for use as light emitting diodes. It has been discovered that when incorporated in a polymer matrix, their decay lifetime can provide accurate measurement of temperature. Their lifetime as a function of temperature depends on three factors: (i) the type and number of ligands in the complex, (ii) the particular polymer used for the matrix, and (iii) the europium chelate to polymer matrix concentration ratio. Various tris and tetrakis europium chelates are used to study ligand effects, while the polymers FIB, polycarbonate, and Teflon(C) are used to analyze matrix effects. In all cases studied, higher concentrations give rise to shorter lifetimes and higher temperature sensitivities, with sensitivity defined as DeltaI/(I(ref)DeltaT). We propose to explain this phenomenon by using the following equation: 1/tau(obs)equivalent toK(total)=k(r)+k(nr)(T)+k(c)([Eu]). Here K-total is the observed decay rate, which is the inverse of the observed lifetime, while k(r) and k(nr)(T) are the radiative and nonradiative decay rates, respectively. As well as being dependent on temperature, k(nr)(T) for these complexes is very dependent on the environment, i.e., solvent or polymer, and can be considered as k(en)(T). The rate k(c)([Eu]) is the quenching term dependent on the concentration of the europium complex. (C) 2004 American Institute of Physics.