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

Abstract

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© 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 ΔI/(IrefΔT). We propose to explain this phenomenon by using the following equation: 1/τobs≡Ktotal=kr+knr(T)+kc([Eu]). Here Ktotal is the observed decay rate, which is the inverse of the observed lifetime, while kr and knr(T) are the radiative and nonradiative decay rates, respectively. As well as being dependent on temperature, knr(T) for these complexes is very dependent on the environment, i.e., solvent or polymer, and can be considered as ken(T). The rate kc([Eu]) is the quenching term dependent on the concentration of the europium complex.

Progress on lanthanide-based organic–inorganic hybrid phosphors

“…Most optical methods for measuring temperature can be grouped into two categories. 51,57,58 The first type of measurements are based on the temperature dependence of the absorption (or the reflection) of certain materials. Examples of this method include thermochromic materials, gas band edge absorptions that shift with temperature, Fabry-Perot interferometers, and changes in refractive indexes.…”

Luminescent Europium(III) Nanoparticles for Sensing and Imaging of Temperature in the Physiological Range

“…[7,8] Among the various known probes, Eu(III) chelates, exhibiting sensitized luminescence that can be excited with visible light, are advantageous over UV-excitable probes for the following reasons (among others): i) Long-wave excitation strongly reduces the background fluorescence of biomatter. ii) Visible excitation is less prone to interferences by inner filter effects due to absorption of light.…”

“…[7] ii) Dinaphthoylmethane (DNM) was reported to efficiently sensitize the luminescence of the Eu(III) ion. iii) The absorption band of DNM extends into the visible part of the spectrum, [14] thus, enabling the use of small and efficient light sources such as LEDs or diode lasers.…”

Photofunctional Lanthanoid Complexes, Coordination Polymers, and Nanocrystals for Future Photonic Applications

“…147 Khalil et al demonstrated the high performance of a Eu(III) complex for a temperature-sensitive paint (temperature sensitivity: 4.42%°C ¹1 ). 148 We had also reported a Tb(III) complex, [Tb(hfa) 3 (H 2 O) 2 ], which is suitable as a temperature-sensing probe since it exhibits effective energy back transfer (BEnT) from the emitting level of the Tb(III) ion to the excited triplet state of the hfa ligand.…”