8 research outputs found
The Nature of Unusual Luminescence in Natural Calcite CaCO 3
Abstract. The unusual luminescence of particular varieties of natural pink calcite (CaCO 3 ) samples was studied by laser-induced time-resolved luminescence spectroscopy at different temperatures. The luminescence is characterized by intense blue emission under short-wave UV lamp excitation with an extremely long decay time, accompanied by pink-orange luminescence under long wave UV excitation. Our investigation included optical absorption, natural thermostimulated luminescence (NTL) and Laser-Induced Breakdown Spectroscopy (LIBS) studies. Two luminescence centers were detected: a narrow violet band, with λ max =412 nm, ∆=45 nm, two decay components of τ 1 =5 ns and τ 2 =7.2 ms, accompanied by very long afterglow, and an orange emission band with λ max =595 nm, ∆=90 nm and τ=5 ns. Both luminescence centers are thermally unstable with the blue emission disappearing after heating at 500 C, and the orange emission disappearing after heating at different temperatures starting from 230 ˚C , although sometimes it is stable up to 500 C in different samples. Both centers have spectral-kinetic properties very unusual for mineral luminescence, which in combination with extremely low impurity concentrations, prevent their identification with specific impurity related emission. The most likely explanation of these observations may be the presence of radiation-2 induced luminescence centers. The long violet afterglow is evidently connected with trapped charge carrier liberation, with their subsequent migration through the valence band and ultimate recombination with a radiation-induced center responsible for the unusual violet luminescence
Silicon photonic acoustic detector (SPADE) using a silicon nitride microring resonator
Silicon photonics is an emerging platform for acoustic sensing, offering exceptional miniaturization and sensitivity. While efforts have focused on silicon-based resonators, silicon nitride resonators can potentially achieve higher Q-factors, further enhancing sensitivity. In this work, a 30 µm silicon nitride microring resonator was fabricated and coated with an elastomer to optimize acoustic sensitivity and signal fidelity. The resonator was characterized acoustically, and its capability for optoacoustic tomography was demonstrated. An acoustic bandwidth of 120 MHz and a noise-equivalent pressure of ∼ 7 mPa/Hz1/2 were demonstrated. The spatially dependent impulse response agreed with theoretical predictions, and spurious acoustic signals, such as reverberations and surface acoustic waves, had a marginal impact. High image fidelity optoacoustic tomography of a 20 µm knot was achieved, confirming the detector’s imaging capabilities. The results show that silicon nitride offers low signal distortion and high-resolution optoacoustic imaging, proving its versatility for acoustic imaging applications
Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications
Thermoelectric
(TE) materials are of utmost significance for conversion
of heat flux into electrical power in the low-power regime. Their
conversion efficiency depends strongly on the microstructure. AgSbTe<sub>2</sub>-based compounds are high-efficiency TE materials suitable
for the mid-temperature range. Herein, we explore an Ag<sub>16.7</sub>Sb<sub>30</sub>Te<sub>53.3</sub> alloy (at %) subjected to heat treatments
at 380 °C for different durations aimed at nucleation and coarsening
of Sb<sub>2</sub>Te<sub>3</sub>-precipitates. To characterize the
Sb<sub>2</sub>Te<sub>3</sub>-precipitation, we use a set of methods
combining thermal and electrical measurements in concert with transmission
electron microscopy and atom probe tomography. We find correlations
between the measured TE transport coefficients and the applied heat
treatments. Specifically, the lowest electrical and thermal conductivity
values are obtained for the as-quenched state, whereas the highest
values are observed for alloys aged for 8 h. In turn, long-term heat
treatments result in intermediate values of transport coefficients.
We explain these findings in terms of interplay between precipitate
formation and variations in the matrix composition, highlighting the
importance of thermal stability of the material under service conditions
Influence of Electrolyte Cations on Ni(Fe)OOH Catalyzed Oxygen Evolution Reaction
Iron-doped,
nickel oxyhydroxide (Ni(Fe)OOH) is one of the
best catalysts for the oxygen evolution reaction (OER) under alkaline
conditions. Due to Ni(Fe)OOH’s layered structure, electrolyte
species are able to easily intercalate between the octahedrally coordinated
sheets. Electrolyte cations have long been considered inert spectator
ions during electrocatalysis, but electrolytes that penetrate into
the catalyst may play a major role in the reaction process. In a joint
theoretical and experimental study, we report the role of electrolyte
counterions (K<sup>+</sup>, Na<sup>+</sup>, Mg<sup>2+</sup>, and Ca<sup>2+</sup>) on Ni(Fe)OOH catalytic activity in alkaline media.
We show that electrolytes containing alkali metal cations (Na<sup>+</sup> and K<sup>+</sup>) yield dramatically lower overpotentials
than those with alkaline earth cations (Mg<sup>2+</sup> and Ca<sup>2+</sup>). K<sup>+</sup> and Na<sup>+</sup> lower the overpotential
because they have an optimal acidity and size that allows them to
not bind too strongly or alter the stability of reaction intermediates.
These two features required for intercalated cation species provide
insight into selecting appropriate electrolytes for layered catalyst
materials, and enable understanding the role(s) of electrolytes in
the OER mechanism
Interlaboratory comparison for quantitative chlorine analysis in cement pastes with laser induced breakdown spectroscopy
International audienceConcrete structures experience severe damage during service, such as pitting corrosion of rebars caused by the ingress of chlorine (Cl) into the porous concrete structure. The ingress can be monitored using laser-induced breakdown spectroscopy (LIBS), a promising civil engineering technique used to detect Cl in concrete structures in addition to conventional wet chemistry methods. The key advantages of LIBS are high spatial resolution, which is important when analyzing heterogeneous concrete samples, as well as the almost complete absence of sample preparation. To assess LIBS as a reliable analytical method, its accuracy and robustness must be carefully tested. This paper presents the results of an interlaboratory comparison on the analysis of Cl in cement paste samples conducted by 12 laboratories in 10 countries. Two sets of samples were prepared with Cl content ranging from 0.06-1.95 wt.% in the training set and 0.23-1.51 wt.% in the test set, with additional variations in the type of cement and Cl source (salt type). The overall result shows that LIBS is suitable for the quantification of the studied samples: the average relative error was generally below 15 %. The results demonstrate the true status quo of the LIBS method for this type of analysis, given that the laboratories were not instructed on how to perform the analysis or how to process the data