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. AgSbTe₂-based compounds are high-efficiency TE materials suitable for the mid-temperature range. Herein, we explore an Ag_16.7Sb₃₀Te_53.3 alloy (at %) subjected to heat treatments at 380 °C for different durations aimed at nucleation and coarsening of Sb₂Te₃-precipitates. To characterize the Sb₂Te₃-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⁺, Na⁺, Mg²⁺, and Ca²⁺) on Ni­(Fe)­OOH catalytic activity in alkaline media. We show that electrolytes containing alkali metal cations (Na⁺ and K⁺) yield dramatically lower overpotentials than those with alkaline earth cations (Mg²⁺ and Ca²⁺). K⁺ and Na⁺ 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

Supplementary document for Silicon-photonics focused ultrasound detector for minimally invasive optoacoustic imaging - 5966521.pdf

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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