Laurent Divay

Near-infrared Fourier transform room-temperature photoluminescence of erbium complexes

A modified Fourier transform (FT) Raman bench spectrometer designed for the detection of weak light emission in the 800–1700 nm wavelength region has been used to demonstrate the advantages of FT spectroscopy for measuring near-infrared photoluminescence spectra of lanthanide complexes with a good resolution and very good sensitivity. This apparatus has been tested with an ultraviolet laser source (325 nm) on three standard erbium complexes. The 4I13/2→4I15/2 emission of tris-(acetylacetonato) (1,10 phenanthroline) erbium [Er(acac)3(phen)], tris-(4,4,4,-trifluoro-1-(2 thenoyl)-1,3-butenedione) (1,10 phenanthroline) erbium [Er(TTFA)3(phen)] and tris(8-hydroxyquinolinato) erbium [Erq3] has thus been recorded in solution and in the solid state and compared with literature.

Concise Multigram-Scale Synthesis of Push-Pull Tricyanofuran-Based Hemicyanines with Giant Second-Order Nonlinearity: An Alternative for Electro-optic Materials

Highly stable and highly soluble push-pull heptamethine hemicyanines based on the tricyanofuran electron-accepting group can be prepared on a 15 g scale. The compounds display giant second-order nonlinear figure of merit, μβ of up to 31,000×10(-48) esu, and lead to a poled material with a second-order nonlinear response, r33 of 90 pm V(-1) at 1.06 μm.

Leaky mode analysis of luminescent thin films: The case of ZnO on sapphire

Zinc oxide (ZnO) epitaxial thin films grown on c-sapphire substrates by pulsed laser deposition were investigated using angle and polarization-resolved photoluminescence spectroscopy. Side-emission spectra differed significantly from surface-emission spectra in exhibiting dominant, narrow, polarization-resolved peaks. These spectral features were attributed to leaky substrate modes in the layers. Observations were first verified using transmission calculations with non-adjustable parameters, which took into account the dispersion, the anisotropy of the ZnO refractive index, and the dependence on film thickness. Results were consistent with Fabry-Perot-like interference being the origin of the distinctive ZnO luminescence observed at grazing incidence angles. A second analysis, based on the source terms method, was used in order to retrieve the bulk emission properties, including the wavelength-dependent quantum yield and the emission anisotropy. While ZnO thin films were considered here, this analysis met...

Free standing thermal interface material based on vertical arrays composites

In power microelectronics, the trends towards miniaturization and higher performances result in higher power densities and more heat to be dissipated. For large systems, the associated thermal architecture is becoming more and more complex and costly. In most electronic assembly, thermal interface materials (TIM) help provide a path for the heat to be transferred from the hot source to a cooler heat sink but still represent a bottleneck in the total thermal resistance of the system. Increasing the dissipative capabilities of thermal interface materials is a widely tackled challenge. For this study we address more specifically the “gap filler” type of TIM. Typically located beneath packaged dies, it features height compensation capabilities, CTE mismatch handling, easy replacement and high thermal conductivity. We report here on the fabrication of a composite free standing film based on vertically aligned carbon nanotubes. Original processing methods are reported as well as first applicability assessments as thermal interface material.

Synthesis and spectroscopic properties of monocyclic and bicyclic erbium phtalocyanines

Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc2 complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device.

Synthesis of some erbium(III) chelates and characterization of their NIR emission properties for use in organic near infrared optical amplification waveguides.

Recent years have seen considerable interest in the possibility of using rare earth chelates as emissive materials in organic media. Lanthanides luminescence is quite interesting in applications requiring high spectral purity (for example in OLEDs), or infra red luminescence, in active optical waveguides for telecommunications. The use of organic optical amplification modules is attractive for their ease of fabrication, and therefore their potential low cost, but the high losses at NIR wavelength and the limitation of the emission lifetime due to the quenching effect of the organic matrix greatly limits their performances. However, rare earth chelates offer the possibility to reduce by several orders of magnitude the pump power needed for population inversion, using the absorption of the organic ligand followed by an energy transfer to the rare earth ion. By choosing a ligand with a high molecular absorption, it should then be possible to balance the short emission lifetime and hence to obtain optical amplification. We report on the synthesis and characterisation of the optical near infrared properties of an erbium phthalocyanine. The complex shows very high absorption in the 670nm region, is highly soluble and shows minimum concentration quenching effect. The red absorption could allow the use of standard laser diode as pump source in a planar polymer amplifier device.

Thermoelectric characterization of nanostructured selenium doped bismuth telluride obtained by a solution route

Thermoelectric devices offer a reliable all solid state solution to active temperature control and are more and more considered as a promising way for thermal management of Integrated Circuits. However, low material performances still represent a hurdle to the spreading of such devices for high power electronics cooling. Enhanced performances bulk materials are needed to access high performance board level cooling, and at the same time very stable processes are needed to ensure repeatability of the materials performances for large scale production. Assembly of nanoparticles obtained by a solution route is an attractive bulk fabrication method in this regard. However, to be effective this solution must give access to fine control of the composition of the material as well. We studied the synthesis of selenium substituted bismuth telluride nanoparticles using a scalable process and characterized the electronic and thermoelectric transport properties of the materials obtained by sintering of these particles.

Thermoelectric property analysis of CsSnX3 materials (X = I, Br, Cl)

The thermoelectric properties of CsSnI₃ are analysed with the ab initio first-principle density functional theory (DFT). Seebeck coefficient, electrical and thermal conductivities are calculated in order to determine the dimensionless figure of merit ZT. Knowing that CsSnI₃ is one of the perovskite series of materials that undergo complex phase transitions with temperature, the calculations are performed for different common phases. Several phases of CsSnBr₃ and CsSnCl₃ are also analysed as comparisons. For the same material, comparison of band structures showed that the band gap increases with phase transition from phase - α to phase - β then to phase - γ. And the ZT values show the same trend as the band gaps. CsSnCl₃ exhibits a higher ZT value than CsSnBr₃ and CsSnI₃ at phase-α.