M. Euler

Solid solution between lithium-rich yttrium and europium molybdate as new efficient red-emitting phosphors

Li3.5Y1.5(MoO4)4 was synthesized in the form of phase-pure crystals. It forms a solid solution with Li3.5Eu1.5(MoO4)4. Single crystals obtained from Li2MoO4 fluxes had edge lengths of up to 0.5 mm. The crystal structures of Li3.5(Y1−xEux)1.5(MoO4)4 (x = 0, 0.1, 0.25, 0.5, 0.75 and 1) were determined in the triclinic crystal system (e.g. P, no. 2, Z = 1; Li3.5Y1.5(MoO4)4: a = 5.1875(2) A, b = 6.6380(2) A, c = 10.2731(4) A, α = 100.082(3)°, β = 100.257(2)° and γ = 111.943(2)°). All the compounds are isostructural and crystallize with a structure related to the scheelite-type structure with mixed occupancy of one cation position, while the two others are occupied by Li ions exclusively. Thermal analyses reveal stability in air up to 995 K for Li3.5Y1.5(MoO4)4; the decomposition temperature decreases with an increase in Eu-content. Spectroscopic properties (emission and excitation) were investigated in the context of the search for new thermographic phosphors. Excitation at 395 nm leads to strong red emission at 613 nm. Features of the emission spectra suggest the potential of Li3.5(Y1−xEux)1.5(MoO4)4 as red phosphor candidates for light emitting diodes. Their luminescence properties at high temperatures were also investigated.

The spectrally resolved luminescence decay of thermographic phosphors

A novel instrumentation for a simultaneous determination of the spectrally and temporally resolved luminescence characteristics of thermographic phosphors is introduced. For this purpose, a spectrometer was combined with a CMOS high-speed camera in order to analyse the materials La2O2S:Eu and LaAlO3:Eu. Lifetime and luminescence intensity plotted against the wavelength as well as luminescence decay curves are presented. Such information in future will guide the best choice for the monitored spectral windows in thermometry applications. The system is shown to be a powerful and efficient tool for a detailed analysis of thermographic phosphors.

A Numerical Study of the Flame Stabilization Mechanism Being Determined by Chemical Reaction Rates Submitted to Heat Transfer Processes

Abstract Large Eddy Simulations of a turbulent lean premixed stratified burner are conducted in order to determine the physical mechanisms that dominate the flame stabilization close to burner walls. The purpose of this work is both to provide insight into the underlying physics as well as to check whether the deficiencies found in previous simulations are related to an inappropriate heat transfer treatment. The simulation utilizes a three-dimensional detailed chemistry database in order to capture the chemical reaction rates based on local mixing and thermal conditions. The study is supplemented by very accurate wall temperature measurements to remove the large uncertainty revealed in the past for this configuration. The results obtained from the simulations are evaluated by means of a qualitative illustration of the different flame stabilizations and comparisons with experimental data.