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The investigation of the fluorescence intensity ratio and the lifetime thermometry techniques for two rare earth perovskites-type oxide (LaGdO3:Er3+ and LaGdO3:Er3+/Yb3+) has been carried out. We have demonstrated that the intensity ratio of thermally coupled levels of erbium (2H11/2 and 4S3/2) is temperature dependant in the range from 283 to 393 K. The sensitivity parameter was found to reach a maximum value of 31 × 10−4 K−1 and 34 × 10−4 K−1 at 393 K and the temperature resolution to be equivalent to 1.61 and 3.1 K, for Er3+ and Er3+/Yb3+ doped oxide, respectively. By studying the temperature dependence of the normalized lifetimes in the range from 293 to 348 K, we proved that the sensitivity of the green emission (4S3/2) is higher than the red one (4F9/2) for both samples, and that it increases from 144 × 10−4 K−1 for LaGdO3:Er3+ to 179 × 10−4 K−1 for LaGdO3:Er3+/Yb3+. The thermal coefficients were quite large in comparison to those calculated for different luminescent materials and reported in literature. The repeatability of measurements was tested by performing heating and cooling cycles for both methods and the results show that these optical techniques have a good repeatability performance. Hence, the LaGdO3: Er3+, Yb3+ oxide has a precise and a satisfying sensitivity associated to a good thermal and chemical stability, suggesting that it can be a potential candidate in temperature sensing.

The importance of non-invasive thermometry based on lifetime fluorescence in biomedical applications imposes the research and development of new phosphors. In this work, sub-tissue lifetime thermal sensing of La2O3: Ln3+ nanomaterials (Ln = Tm, Er and Yb) has been studied. Two oxides are investigated: Er3+, Tm3+, Yb3+ tri-doped La2O3 and Tm3+, Yb3+ co-doped La2O3. We have focused on the lifetime of the 1G4→3H6 transition that corresponds to the blue emission of Tm3+ ion, recorded at 480 nm. We prove that tri-doped oxide has remarkable higher thermal sensitivity than the co-doped one, with a temperature coefficient estimated to 6.7 × 10−3 °C−1, which is comparable to that of nanomaterials oxides previously studied for luminescence thermometry and reported in literature. We have described the setup used to carry out the sub-tissue lifetime thermal sensing realized on biological tissue in the temperature range between 25 °C and 60 °C.

A series of LaEr(1−x)YbxO3 (x=0, 0.01 and 0.05) samples were prepared with a combustion method and characterized by FTIR, Raman spectroscopy and X-ray diffraction. The optical properties of samples were studied upon laser excitations. The upconversion emission spectra registered under excitation at 980 nm show the presence of the typical erbium emission bands and that the higher intensity is given by sample with 5% of ytterbium concentration. The variation of upconversion intensity as a function of laser power of the LaEr0.95Yb0.05O3 sample reveals that two photons are implicated in the upconversion mechanism and that the lifetime of the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 emissions of this sample is estimated to 12.3 and 97.7 µs, respectively. The calculated CIE chromaticity coordinates of the phosphor samples show that the green emission is dominant, and that its intensity increases by substituting erbium with 1% or 5% of ytterbium. The effect of ytterbium concentration on optical band gap shows that the gap energy value tends to decrease from 4.25 eV to 4.14 eV for 0% and 5% of ytterbium concentration, respectively. The increase in intensity of green emission by adding ytterbium to LaErO3 classifies these oxides as phosphor materials that could have applications in bioimaging of cells.

International audience; This work reports a reduced dimensionality rate constant calculation of the H-abstraction reaction from formaldehyde. Quantum scattering calculations are performed treating explicitly the bonds being broken and formed. Geometry optimisations and frequency calculations are done at the MP2/cc-pVTZ level while energies are calculated with the CCSD(T) method. An analytical potential energy surface was developed from a relatively small number of grid points. When compared to semi-classical approaches, the quantum scattering calculations show that quantum tunnelling yields large contributions at low temperatures. At 200 K, we note a difference of about 5 orders of magnitude between Transition State Theory (TST) and quantum rate constants. Our predicted results show that the quantum and the CVT/SCT rate constants are in reasonable agreement with the available experiment at high temperatures, but that the last one gives better agreement to experimental results at low temperatures.

We have investigated the electrical and dielectric properties of rare earth perovskites-type oxide (LaErO3 and LaHoO3) by using impedance spectroscopy, respectively, over a frequency and temperature range of [0.6 kHz–8 MHz] and [673–973 K]. Both oxides crystallize in the orthorhombic structure but exhibit difference in lattice distortions. A correlation between structural properties and dielectric anisotropies is carried out. The analysis of Nyquist semicircles confirms the presence of bulk effects and non-Debye relaxation processes for both compounds. The activation energy, calculated using relaxation time and direct current conductivity models, was found to follow the Arrhenius law. The frequency dependence of alternative current conductivity is described by Jonscher's universal power law and shows that the conduction mechanism follows the non-overlapping small polaron tunneling model. The investigation of dielectric properties revealed that at low frequencies the dielectric constant was higher for LaHo...