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Quantum radiation from a shaken two-level atom in vacuum
摘要： We present a nonrelativistic theory of quantum radiation generated by shaking a two-level atom in vacuum. Such radiation has the same origin of photon emission in dynamical Casimir effect. By performing a time-dependent “dressing” transformation to the Hamiltonian, we derive an interaction term that governs the radiation. In particular, we show that photon pairs can be generated, not only by shaking the position of the atom, but also by changing the internal states of the atom. As applications of our theory, we calculate the emission rate from an oscillating atom and the multiphoton state generated in a single-photon scattering process.
关键词： time-dependent dressing transformation,two-level atom,dynamical Casimir effect,quantum radiation,photon emission
更新于2025-09-09 09:28:46
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Fluorometric determination of hydroquinone by using blue emitting N/S/P-codoped carbon dots
摘要： N/S/P-codoped carbon dots (CDs) are shown to be a viable fluorescent probe in a turn-off-on fluorometric assay for hydroquinone (HQ). The preparation of CDs was carried out using a one-step hydrothermal reaction starting with glyoxal and isocarbophos. The method is based on the formation of ground state complexes between CD and Fe(III) which leads to quenching of blue fluorescence (with excitation/emission peaks at 363/448 nm). On addition of HQ, it will be oxidized by Fe(III) upon which fluorescence recovers. This turn-off-on system can be utilized to quantify HQ. A linear relationship exists between fluorescence recovery and HQ concentration in range between 0.56 and 375 μM. The limit of detection is 0.16 μM. The assay was successfully applied to the determination of HQ in spiked water samples and developer samples.
关键词： Developer samples,Blue emission,1,4-dihydroxybenzene,Glyoxal,Fluorescence turn-off-on system,Heteroatoms,Carbon dots,Water samples,Hydrothermal reaction,Fe(III)
更新于2025-09-09 09:28:46
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An Optical Emission Spectroscopy Study of Plasma–Precursor Interactions in Solution Precursor Plasma Spray
摘要： In this work, optical emission spectroscopy is used to study plasma–liquid precursor interactions in a plasma spray process. A mapping of the plasma jet is performed with a bundle of seven optical fibers while injecting various liquid precursors. The decomposition of two suspensions containing a titania (TiO2) powder in different solvents and that of one solution containing titanium butoxide is analyzed inside a radio frequency thermal plasma. For each precursor, the evolution of both temperature and titanium density along the plasma jet is observed. Two different plasma compositions were used to study their effects on the precursor decomposition. For each experiment, x-ray diffraction was performed on the collected powder to correlate OES observations with the structure and composition of the powder. Comparing these results brings a new understanding of the precursor decomposition inside the plasma, while the noted contrasts between water and ethanol as solvent, and between the use of a powder and that of an alkoxide as a source of titanium, help to assess the effect of these parameters on the plasma spray process.
关键词： titanium dioxide,optical emission spectroscopy,suspension plasma spray,plasma–precursor interactions,solution precursor plasma spray
更新于2025-09-09 09:28:46
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Light Emission by Nanoporous GaN Produced by a Top-Down, Nonlithographical Nanopatterning
摘要： Temperature-dependent photoluminescence (PL) spectroscopy is carried out to probe radiative recombination and related light emission processes in two-dimensional periodic close-packed nanopore arrays in gallium nitride (np-GaN). The arrays were produced by nonlithographic nanopatterning of wurtzite GaN followed by a dry etching. The results of Raman spectroscopy point to a small relaxation of the compressive stress of ~0.24 GPa in nanoporous vs. bulk GaN. At ~300 K, the PL emission is induced by excitons and not free-carrier interband radiative recombinations. An evolution of the emission spectra with T is con?rmed to be mainly a result of a decay of nonexcitonic PL emission and less of spectral shifts of the underlying PL bands. A switching of excitonic PL regime observed experimentally was analyzed within the exciton recombination-generation framework. The study provides new insights into the behaviors and physical mechanisms regulating light emission processes in np-GaN, critical to the development of nano-opto-electronic devices based on mesoscopic GaN.
关键词： photoluminescence,nonlithographic nanopatterning,Raman spectroscopy,nanoporous GaN,excitonic emission
更新于2025-09-09 09:28:46
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Probing the Aggregation and Signaling Behavior of Some Twisted 9,9′-Bianthryl Derivatives: Observation of Aggregation-Induced Blue-Shifted Emission
摘要： With an aim to understand the photophysical behavior of twisted organic fluorescent molecules in their aggregated state, two twisted biaryl molecules, namely, 9,9′-bianthryl and 10,10′-dicyano-9,9′-bianthryl, have been synthesized and characterized by conventional spectroscopic methods. To understand the role of C?C bond twisting on the photophysical response of biaryl aggregates, monoaryl counterparts (anthracene and 9-anthracenecarbonitrile) of the biaryl systems are also investigated. Photophysical behaviors of these systems along with their monoaryl counterpart are investigated in both solution and aggregated state. Investigations reveal that fluorescence spectra of the biaryl compounds show blue-shifted emission upon aggregation. Interestingly, no blue shift of the emission has been observed for monoaryl aggregates. Photophysical data of biaryl systems compared to monoaryl unit reveal that change in geometry, during self-assembly process, disfavors the formation of charge-transfer state, which eventually causes blue shift in the emission upon aggregation. In addition to this, potential of these systems toward signaling of nitroaromatic explosive has also been explored. Among all of the nitroaromatics, the highest fluorescence quenching is observed for nitrophenols (say picric acid (PA)). The investigation also reveals that compared to monoaryl systems, biaryl systems are more responsive to fluorescence quenching by nitroaromatics. Perrin’s model of quenching sphere action has been attributed to nitrophenol (PA) selective signaling behavior of biaryl systems.
关键词： aggregation-induced blue-shifted emission,twisted biaryl molecules,fluorescence quenching,photophysical behavior,nitroaromatic explosives
更新于2025-09-09 09:28:46
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Lead-Free Direct Bandgap Double Perovskite Nanocrystals with Bright Dual-Color Emission
摘要： Lead-free double perovskite nanocrystals (NCs), i.e. Cs2AgInxBi1?xCl6 (x = 0, 0.25, 0.5 0.75 and 0.9), that can be tuned from the indirect bandgap (x = 0, 0.25 and 0.5) to the direct bandgap (x = 0.75 and 0.9) are designed. Direct-bandgap NCs exhibit 3 times greater absorption cross-section, lower sub-bandgap trap states, and >5 times photoluminescence quantum efficiency (PLQE) compared with those observed for indirect bandgap NCs (Cs2AgBiCl6). A PLQE of 36.6% for direct bandgap NCs is comparable to those observed for lead-perovskite NCs in the violet region. Besides the band edge violet emission, the direct bandgap NCs exhibit bright orange (570 nm) emission. Density functional theory calculations suggesting forbidden transition is responsible for the orange emission, which is supported by time resolved PL and PL excitation spectra. The successful design of lead-free direct bandgap perovskite NCs with superior optical properties opens the door for high performance lead-free perovskite optoelectronic devices.
关键词： dual-color emission,direct bandgap,Lead-free,photoluminescence quantum efficiency,double perovskite nanocrystals
更新于2025-09-09 09:28:46
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Dual sites fluorescence probe for hydrogen sulfide: AIEE activity and supramolecular assembly with β-cyclodextrin
摘要： One aggregation-induced emission enhancement (AIEE) active compound based on α–cyanostilbenes and maleic anhydride group were synthesized. The “Turn-On” fluorescence recognition for H2S was evaluated both in aqueous solution and cells. It was found that cyanostilbenes group acts as the first reactive site and maleimide group acts as the second site to H2S. Supramolecular assembly with β-cyclodextrin successfully revealed the reaction mechanism of 3-state model.
关键词： α–cyanostilbenes,Hydrogen sulfide,Supramolecular assembly,Maleic anhydride,Aggregation–induced emission
更新于2025-09-09 09:28:46
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Applied Nanophotonics || Quantum confinement effects in semiconductors
摘要： Absorption and emission of light by atoms, molecules, and solids arise from electron transitions. Electron confinement phenomena in solids with restricted geometry like nanoparticles, nanorods, or nanoplatelets gives rise to the modification of optical absorption and emission spectra and transition probabilities in semiconductor nanostructures. These phenomena are direct consequences of the wave properties of electrons. In this chapter we describe size-dependent optical properties of semiconductor nanostructures related to quantum confinement.
关键词： optical absorption,semiconductors,nanostructures,emission spectra,Quantum confinement
更新于2025-09-09 09:28:46
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Applied Nanophotonics || Spontaneous emission of photons and lifetime engineering
摘要： Excited atoms, molecules, and solids emit spontaneously photons, with the rate of emission being dependent both on their intrinsic properties and the properties of ambient space. The latter is capable or not capable of carrying on certain electromagnetic modes. This property of space is described by means of the density of electromagnetic modes or, in quantum language, photon density of states. Photon density of states can be engineered in a desirable way using spatially arranged components with different dielectric permittivity on the wavelength scale. This chapter provides a brief introduction to spontaneous photon emission control in nanostructures based on confinement of electromagnetic waves to get photon density of states’ enhancement or inhibition.
关键词： nanostructures,electromagnetic waves,spontaneous emission,photon density of states,lifetime engineering
更新于2025-09-09 09:28:46
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Applied Nanophotonics || Stimulated emission and lasing
摘要： Stimulated transitions in quantum systems represent the principal background for laser operation. Lasers play important roles in daily life and form a valuable part of photonics. Though the first lasers were supposed to have an impact on material processing owing to extreme energy concentration, currently the main applications of lasers are not based on high-energy abilities, but essentially on their compactness, cheapness, and efficiency. Optical communication, laser printers, and DVD players are the most common laser applications, and here semiconductor lasers are definitely unsurpassed. In this chapter we provide a brief introduction to the principles of laser operation and laser device engineering to emphasize where nanostructures can be useful and which components of lasers can be improved by means of nanophotonic solutions. Because of the scope of this book, a brief explanatory style is used which may confuse laser experts but at the same time may still appear complicated for newcomers. This chapter may appear complicated for readers not at all familiar with lasers, and in this case appropriate textbooks are suggested for further reading.
关键词： quantum systems,lasing,stimulated emission,optical gain,semiconductor lasers
更新于2025-09-09 09:28:46