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Color-center formation and thermal recovery in X-ray and electron-irradiated magnesium aluminate spinel
摘要： We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 10^18 cm^?2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VO^x) and singly ionized (VO^.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.
关键词： thermal recovery,X-ray irradiation,color centers,threshold displacement energy,F centers,electron irradiation,absorption spectroscopy,magnesium aluminate spinel
更新于2025-09-23 15:23:52
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Ferroelastic phase transition in Cu <sub/>6</sub> PS <sub/>5</sub> Br <sub/>1-x</sub> Cl <sub/>x</sub> mixed crystals
摘要： Cu6PS5Br1-xClx mixed crystals were grown by chemical vapour transport. Optical absorption edge and optical polarization measurements were performed in the temperature range 77–320 K. The in?uence of anionic Br→Cl substitution on the phase transitions in Cu6PS5Br1-xClx mixed crystals is studied. Compositional dependence of the ferroelastic phase transition temperature for Cu6PS5Br1-xClx mixed crystals is obtained. The variation of optical parameters at ferroelastic phase transition is analyzed.
关键词： absorption edge,optical parameters,phase transition,mixed crystals,Ferroelastic
更新于2025-09-23 15:23:52
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Controlling the emission and absorption spectrum of a quantum emitter in a dynamic environment
摘要： We study the emission spectrum and absorption spectrum of a quantum emitter when it is driven by various pulse sequences. We consider the Uhrig sequence of nonequidistant πx pulses, the periodic sequence of πxπy pulses and the periodic sequence of πz pulses (phase kicks). We find that, similar to the periodic sequence of πx pulses, the Uhrig sequence of πx pulses has emission and absorption that are, with small variations, analogous to those of the resonance fluorescence spectrum. In addition, while the periodic sequence of πz pulses produces a spectrum that is dependent on the detuning between the emitter and the pulse carrier frequency, the Uhrig sequence of nonequidistant πx pulses and the periodic sequence of πxπy pulses have spectra with little dependence on the detuning as long as it stays moderate along with the number of pulses. This implies that they can also, similar to the previously studied periodic sequence of πx pulses, be used to tune the emission or absorption of quantum emitters to specific frequencies, to mitigate inhomogeneous broadening and to enhance the production of indistinguishable photons from emitters in the solid state.
关键词： spectral diffusion,emission/absorption spectrum,solid state emitter,pulse-driven emitter
更新于2025-09-23 15:23:52
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Fabrication and characterisation of viscose fibre with photoinduced heat-generating properties
摘要： In the field of functional textile research, heat-generating fibres to maintain body temperature without unsustainable energy input are of interest. Here, we propose a photoinduced heat-generating viscose fibre fabricated by adding zirconium carbide (ZrC) to the viscose solution. Viscose nonwoven fabrics comprising ZrC-doped viscose fibres were irradiated by infrared (IR) light to measure their surface temperatures, thereby determining their light-to-heat conversion effects. The results show that the surface temperature of the viscose fabric doped with 4% ZrC was increased by almost 40 °C, as verified by ultraviolet–visible–near-IR (NIR) spectroscopy, indicating that the ZrC-doped viscose fibre was significantly increased in photon absorption in the visible-light and NIR regions. The cross-sectional morphology of the viscose fibre was observed using a scanning electron microscope. In addition, thermogravimetric analysis was used to determine the thermal decomposition behaviour of the doped viscose fibres. Moreover, it is noticed that the ZrC-doped viscose fibre has lower moisture regain, potentially increasing the wet strength of the viscose fibre.
关键词： Zirconium carbide,Photoinduced heat-generation,Viscose fibre,Light absorption
更新于2025-09-23 15:23:52
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Atom localization using Laguerre-Gaussian beams
摘要： Use of the Laguerre-Gaussian beams in an atom-light interaction makes the linewidth of the optical spectrum narrow. We exploit this fact for providing the ability to accomplish simultaneous ultra-high precision and spatial resolution atom localization in a double-Λ atomic system; under multi-photon resonance condition, the resolution of the localization is remarkably improved so that the atom can be localized in a region smaller than λ/100 × λ/100. Most prominently, the probability of finding the atom at a particular position is always 100%, when a photon with certain frequencies is absorbed or amplified. Such features are mainly attributed to radial dependence associated with the Laguerre-Gaussian beams in a spatially dependent atom-light interaction.
关键词： Laguerre-Gaussian beams,probe absorption,2D atom localization
更新于2025-09-23 15:23:52
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To the Theory of the Polarized Radiation Absorption in a Semiconductor (001) Quantum Well
摘要： The paper considers absorption of linearly polarized radiation in a semiconductor size-quantized well related to optical transitions both between the branches of light and heavy holes and between the size-quantized subbands. Main features of the light absorption in an infinitely deep symmetric well are elucidated. These features are characterized by intraband absorption of light and associated with the direct optical transitions of holes between the subbands of the semiconductor valence band formed due to the size quantization.
关键词： optical transition,semiconductor,size quantization,light absorption coefficient,polarized light,holes
更新于2025-09-23 15:23:52
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Spectral and third order nonlinear optical properties of Yttrium-doped BaWO4 nanostructures
摘要： BaWO4 nanostructures doped with different concentrations of Yttrium have been synthesized by a chemical method. The as-prepared samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopy and Raman spectra. From the UV–vis spectra, it is seen that absorption band edge shifted towards the visible region upon Y doping. The X-ray diffraction and Raman analyses reveal that the BaWO4 powders present a tetragonal structure. The third-order nonlinear optical responses of BaWO4 nanostructures on the effect of Y concentrations was investigated by Z-scan technique using a continuous wave Nd:YAG laser at 532 nm. Experimental results have shown that the observed nonlinear absorption and nonlinear refraction behavior is attributed to saturable absorption and thermal nonlinear effects.
关键词： Nanostructures,Yttrium,Saturable absorption,Z-scan
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on Computational Electromagnetics (ICCEM) - Chengdu (2018.3.26-2018.3.28)] 2018 IEEE International Conference on Computational Electromagnetics (ICCEM) - A Novel Band-Notched UWB Conformal Antenna Combined with the Method of Circuitry
摘要： A real-time latching controller with consideration of wave force prediction is developed and applied to a heaving point-absorber to maximize its energy absorption. The control scheme is based on the combination of optimal command theory and first order-one variable grey model GM(1,1). By forecasting the wave forces in the near future, the control action at the next instant is deduced. Simulation results show that the energy absorption is increased due to the real-time controller. Therefore, the developed real-time controller is applicable to an industrial wave energy converter (WEC) in random waves. The effect of wave force prediction deviation is also examined. It is shown that the control efficiency is reduced in the presence of prediction deviation.
关键词： wave energy converter,wave force prediction,renewable energy,optimal command theory,energy absorption,real-time latching control
更新于2025-09-23 15:23:52
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Fingerprints of sp1 Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials
摘要： Carbon structures comprising sp1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp1/sp2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp1/sp2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp2 systems. We then consider a mixed polymer alternating sp1 C4 units with sp2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp1 hybridization in surface-grown C structures.
关键词： density functional theory,self-assembly,carbynes,on-surface chemistry,near edge X-ray absorption spectroscopy,C 1s absorption
更新于2025-09-23 15:22:29
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Transition from Two-photon Absorption to Saturable Absorption in Gold Patterned Ruby Thin Film
摘要： Nonlinear behaviour of gold micro disks patterned Ruby film has been investigated via Z-scan technique. Open Z-scan was performed for Ruby and Ruby/gold thin film using 532 nm Laser source. Two-photon absorption (TPA) and Saturable absorption (SA) have been observed in pure Ruby and Ruby/gold thin film respectively. The expression for normalized transmittance in open Z-scan was obtained by Gaussian decomposition method for fitting the open. The values for nonlinear absorption coefficient (β) for Ruby/gold (7.41 × 10?7??/??) was two orders of magnitude higher than that of Ruby (1.41 × 10?9??/??). Further, TPA and SA were confirmed by open Z-scan on these films, performed by 633 nm Laser source.
关键词： Surface Plasmon Resonance,Ruby,Z-scan,Two-photon absorption,Saturable absorption
更新于2025-09-23 15:22:29