Sonoluminescence of elementary sulfur melt

The sonoluminescence of liquid sulfur has been observed for temperatures of 120–180°C. The sonoluminescence intensity of the sulfur melt is 10⁹ photons/s at 120°C. As the temperature increases, the luminescence intensity decreases nonmonotonically, a maximum is observed at 160–175°C, and cavitation and luminescence cease at 180°C. The dependence obtained correlates with the temperature dependence of the viscosity of the sulfur melt. The sonoluminescence spectrum obtained with a resolution of 10 nm for 130–150°C contains one band with λ_max = 560 nm, the emitter of which is likely an (S⁺)* ion. When the melt is saturated with argon, the sonoluminescence intensity increases by an order of magnitude; in this case, the spectral band shape changes only slightly. The results confirm the “electric” theory of multibubble sonoluminescence. In the process of the sonolysis of the sulfur melt, biradical fragments are formed in cavitation bubbles consisting of sulfur molecules, which initially have the form of cyclooctasulfur S₈. These fragments can enter into the melts and can be involved in various chemical reactions. This circumstance makes it possible to recommend ultrasonic activation for reactions of sulfurization of hydrocarbons.     

Sonochemiluminescence in an aqueous solution of Ru(bpy)3Cl2

The sonochemiluminescence spectra of electron-excited ions ^*[Ru(bpy)₃]²⁺ was registered for the first time during sonolysis of argon saturated aqueous solutions of Ru(bpy)₃Cl₂ with low concentration. At single-bubble sonolysis, the luminescence band of ruthenium is recorded at a concentration of Ru(bpy)₃Cl₂ from 10⁻⁶ M, and at multibubble from 10⁻⁵ M. Possible mechanisms for the appearance of the band of a tris-bipyridyl ruthenium(II) complex on the background of an structureless continuum of water in the spectra of sonoluminescence are analyzed. Based on the results of the comparison of the sonoluminescence spectra of Ru(bpy)₃Cl₂ aqueous solutions with the sonoluminescence spectra of aqueous solutions of rhodamine B (which has a high quantum yield of photoluminescence) it was established that a possible mechanism of sonophotoluminescence does not play a decisive role in ruthenium sonoluminescence. The effect of radical acceptors (O₂, C₂H₅OH, Cd²⁺, I⁻) on ruthenium sonoluminescence is analyzed. The most significant mechanism for the formation of electron-excited ions ^*[Ru(bpy)₃]²⁺ during sonolysis is the sonochemiluminescence in oxidation-reduction reactions involving [Ru(bpy)₃]²⁺ ions and radical products of sonolysis of water (OH, H, e⁻_aq) in the solution volume.     

Anomalous isotopic effect in multibubble sonoluminescence of aqueous solutions of terbium chloride

An anomalously low isotope effect has been discovered in 20-kHz sonoluminescence of terbium chloride solutions in H₂O-D₂O mixtures. The intensity of luminescence in the characteristic 488-and 545-nm lines of the Tb³⁺ ion, which are observed against the solvent continuum (230–700 nm), increases with the content of D₂O to a maximum value of 4.0 ± 0.4, whereas the isotope effect in photoluminescence of the same solutions reaches 10 ± 1.0. The result is explained using the model of nonexponential decay of sonoluminescence of Tb³⁺ ions. These ions, which are formed in an excited state in cavitation bubbles, first undergo radiative and radiationless deactivation in the gas phase. However, some excited ions enter the solution bulk, because the excitation lifetime is longer than the average bubble lifetime. At the first stage, the isotope effect is small, because the density of the gas phase is low and quenching by solvent molecules is weak. At the second stage, the isotope effect coincides with the effect in usual photoluminescence in the solution. The total decrease in the effect in sonoluminescence depends on the weight of the “gas” stage of deactivation of excited Tb³⁺ ions.     

Sonoluminescence

Abstract

Sonoluminescence is the light emission phenomenon from collapsing bubbles in liquid irradiated by an ultrasonic wave. In the present review, theoretical and experimental studies of the two types of sonoluminescence [single‐bubble sonoluminescence (SBSL) and multibubble sonoluminescence (MBSL)] are described. SBSL is a sonoluminescence from a single stably pulsating bubble trapped at the pressure antinode of a standing ultrasonic wave. MBSL is a sonoluminescence occurring from many bubbles in liquid irradiated by an ultrasonic wave. The theoretical and experimental studies suggest that SBSL originates in emissions from plasma inside the heated bubble at the bubble collapse, whereas MBSL originates both in emissions from plasma and in chemiluminescence inside heated bubbles at the bubble collapse. Unsolved problems of sonoluminescence have also been explained in detail.     

Single-bubble sonoluminescence of aqueous solutions of lanthanide chlorides and models of the sonochemistry of nonvolatile metal salts

The single-bubble sonoluminescence of d-f (Ce³⁺, Pr³⁺) and f-f (Tb³⁺) ions is detected in aqueous solutions of LnCl₃. It has been shown that the luminescence of these ions is sonophotoluminescence, i.e., the reemission of the absorbed short-wavelength part of the radiation spectrum of a blackbody, which appears in a bubble levitating in the field of a standing ultrasonic wave, in the bulk of the solution. In view of the revealed inefficiency of reemission in GdCl₃, the single-bubble sonoluminescence of Gd³⁺ has not been observed. The results indicate the low probability of the penetration of nonvolatile metal ions into the bubble in the hot shell model, which would be valid in single-bubble sonolysis and thereby confirm the validity of the injected droplet model, which explains the penetration to the bubble, electronic excitation, and luminescence of f-f ions Gd³⁺ and Tb³⁺ in multibubble sonolysis with an intensity much higher than the yield of their sonophotoluminescence.     

Strong green luminescence of Ni2+-doped ZnS nanocrystals

ZnS nanoparticles doped with Ni²⁺ have been obtained by chemical co-precipitation from homogeneous solutions of zinc and nickel salt compounds, with S^2- as precipitating anion, formed by decomposition of thioacetamide (TAA). The average size of particles doped with different mole ratios, estimated from the Debye–Scherrer formula, is about 2–2.5 nm. The nanoparticles could be doped with nickel during synthesis without altering the X-ray diffraction pattern. A Hitachi M-850 fluorescence spectrophotometer reveals the emission spectra of samples. The absorption spectra show that the excitation spectra of Ni-doped ZnS nanocrystallites are almost the same as those of pure ZnS nanocrystallites (λ_ex=308–310 nm). Because a Ni²⁺ luminescent center is formed in ZnS nanocrystallites, the photoluminescence intensity increases with the amount of ZnS nanoparticles doped with Ni²⁺. Stronger and stable green-light emission (520 nm) (its intensity is about two times that of pure ZnS nanoparticles) has been observed from ZnS nanoparticles doped with Ni²⁺. Received: 18 December 2000 / Accepted: 17 March 2001 / Published online: 20 June 2001     

A novel approach for the synthesis of superparamagnetic Mn3O4 nanocrystals by ultrasonic bath

In this study, the synthesis of Mn₃O₄ (husmannite) nanoparticles was carried out in two different alkali media under sonication by ultrasonic bath and conventional method. Manganese acetate was used as precursor, sodium hydroxide and hexamethylenetetramine (HMT) as basic reagents in this synthesis. An ultrasonic bath with low intensity was used for the preparation of nanomaterials. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. The XRD patterns exhibit the nanocrystals are in pure tetragonal phase. The chemical composition was obtained by EDS analysis and confirmed the presence of Mn and O in the sample. According to the TEM and HRTEM results, both nanorods and nanoparticles of Mn₃O₄ were obtained in the presence of ultrasonic irradiation. The average size of nanoparticles was 10 nm, and the size of nanorods was 12 nm in diameter and 100-900 nm in length for the samples prepared in basic medium with sodium hydroxide. In the conventional method with the same basic medium, the nanorod was not observed and the nearly cubic nanoparticles was appeared with an average size of 2.5 nm. The selected area electron diffraction (SAED) patterns revealed that the nanocrystals are polycrystalline in nature. When HMT was used as a basic reagent in the presence of ultrasonic irradiation, it was led to a higher size of nanoparticles and nanorods than when sodium hydroxide was used as a basic reagent. The average size of nanoparticles was about 15 nm and its shape was nearly cubic. The diameter for nanorods was 50 nm and the length was about a few micrometers.The magnetic measurements were carried out on the sample prepared in sodium hydroxide under ultrasonic irradiation. These measurements as a function of temperature and field strength showed a reduction in ferrimagnetic temperature (T_c = 40 K) as compared to those reported for the bulk (T_c = 43 K). The superparamagnetic behavior was observed at room temperature with no saturation magnetization and hysteresis in the region of measured field strength.     

Multi-bubble sonoluminescence of phosphoric acid

Multi-bubble sonoluminescence spectra of 85% H₃PO₄ and the dependences of sonoluminescence intensity on the acid concentration and temperature are obtained. The spectra contain a weakly structured 300–600-nm band formed by the superposition of radiation from several emitters (presumably, oxygencontaining products of acid sonolysis, viz., PO, HOPO, and PO₂). Weak luminescence at a wavelength exceeding 600 nm can be due to emission from excited O* and Ar* atoms. The shape of the fundamental band changes upon a transition from multi-bubble sonolysis to sonolysis in the setup for one-bubble sonoluminescence, in which several clusters of cavitation bubbles are formed in a spherical flask at ultrasonic frequencies multiple of the first acoustic resonance frequency (multi-cluster sonoluminescence). The form of the temperature dependence of the sonoluminescence intensity depends on the detection regime: for natural heating of 85% acid under the action of ultrasound, a curve with a luminescence peak at 40°C is observed, while in detection with preliminary thermostating “over points,” only an inflection exists on a monotonic curve describing a decrease of intensity upon heating. An analogous curve for acids with a lower viscosity (hydrochloric and nitric acids) has neither a peak nor inflection irrespective of the detection regime. It is concluded that the viscosity of phosphoric acid plays a decisive role in the evolution of cavitation and in obtaining intense sonoluminescence.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

The size of active bubbles for the production of hydrogen in sonochemical reaction field

The sonication of aqueous solution generates microscopic cavitation bubbles that may growth and violently collapse to produce highly reactive species (i.e. OH, HO₂ and H₂O₂), hydrogen and emit light, sonoluminescence. The bubble size is a key parameter that influences the chemical activity of the system. This wok aims to study theoretically the size of active bubbles for the production of hydrogen in ultrasonic cavitation field in water using a single bubble sonochemistry model. The effect of several parameters such as frequency of ultrasound, acoustic intensity and liquid temperature on the range of sonochemically active bubbles for the production of hydrogen was clarified. The numerical simulation results showed that the size of active bubbles is an interval which includes an optimum value at which the production rate of H₂ is maximal. It was shown that the range of ambient radius for an active bubble as well as the optimum bubble radius for the production of hydrogen increased with increasing acoustic intensity and decreased with increasing ultrasound frequency and bulk liquid temperature. It was found that the range of ambient bubble radius dependence of the operational conditions followed the same trend as those reported experimentally for sonoluminescing bubbles. Comparison with literature data showed a good agreement between the theoretical determined optimum bubble sizes for the production of hydrogen and the experimental reported sizes for sonoluminescing bubbles.     

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT

According to the spectra of stationary X-ray excited luminescence (XEL) of BaF₂: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d?=?35?nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120?nm, does not result in effective changes of the charge state of Eu^{3 +} → Eu^{2 +} activator, in contrast to CaF₂: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF₂: Eu nanophosphors in the 590?nm emission band of Eu³⁺ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67?nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF₂: Eu nanoparticles of 58?nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu³⁺ → Eu²⁺ under the influence of long-time X-ray irradiation was revealed for the peak of 151?K. Thus, X-ray excited luminescence spectra of BaF₂: Eu nanophosphors are formed predominantly due to the emission of Eu³⁺ ions, while emission of Eu²⁺ ions is observed in the TSL spectra.     

有机溶液中圆锥泡声致发光

在U形管声致发光装置的基础上建立了一套新型的声致发光装置——直管圆锥泡声致发光装置. 利用此装置以有机溶液为液体介质得到了超强的发光脉冲并测量得到了其发光光谱. 结果表明发光光谱为一从紫外光至可见光波长范围的连续谱,上面叠加有C₂的d³Π_g→d³Π_u跃迁形成的五个序列谱带,分别对应于Δv=-2,Δv=-1,Δv=0,Δv< 关键词： 声致发光 光谱 斯旺带 振动温度     

Spectroscopy of Nickel-Doped Zinc Sulfide Nanoparticles

ABSTRACT

In the present study, Zn_1?xNi_xS (x = 0.0–0.8 mol%) nanoparticles were prepared through the chemical route and the synthesis involved the mixing and drying of zinc acetate and sodium sulphide in an appropriate ratio with the addition of Ni²⁺ at a proper concentration. The structural and spectroscopic studies are investigated by X-ray diffraction (XRD), absorption spectra, emission and excitation spectra, and Raman spectra. Compared with that of the pristine materials, the absorption band-edge demonstrates an apparently blue shift, which is attributed to the quantum size effect. The average particle size of ZnS nanoparticles is in the range of 2–4 nm deduced from the XRD line broadening. Excited at about 330 nm, a blue emission band at 425 nm can be observed, which corresponds to Ni²⁺ luminescent center; this result is consistent with the postulation that Ni²⁺ replaced the Zn²⁺ ions in the lattice of ZnS nanocrystals. Excitation spectra also confirm the above postulation. The effect of different concentrations of nickel is also studied by Raman spectra.     

Photoluminescent silicon nanocrystals stabilized by ionic liquid

Silicon nanocrystals stabilized by an ionic liquid, dimethylimidazolium iodide, were synthesized by chemical reduction of SiBr₄ with metallic Na in an organic solvent, diglyme. The nanoparticles were crystalline with a diamond cubic lattice and average size of 3.5 nm. Solid state ¹³C- and ²⁹Si-NMR CP MAS spectra indicate the formation of imidazolium carbene, which ligates the Si atoms at the surface of the nanoparticles. The synthesized Si nanoparticles exhibit photoluminescence with an emission maximum in the red spectral range when excited at 320 nm. The origin of this luminescence is suggested to be mainly related to quantum confinement.     

Dextran‐Coated Antiferromagnetic MnO Nanoparticles for a T1‐MRI Contrast Agent with High Colloidal Stability

A simple approach to synthesize carboxymethyl dextran‐coated MnO nanoparticles (CMDex‐MnONPs) with high colloidal stability in physiological saline solutions is described here for potential applications as a magnetic resonance imaging (MRI) T₁ contrast agent. The thermal decomposition methodology is used to produce uniform MnONPs with an average size of around 20 nm, and its hydrophobic surface is modified with CMDex molecules, conferring hydrophilic properties. After CMDex coating, the nanoparticle presents high colloidal stability in concentrations ranging from 10 to 50 μg mL^?1, average hydrodynamic size (Z‐average) of 130 nm, polydispersity degree of ≈12%, and negative surface charge in both simulated body fluid solutions and pure water with zeta‐potential of –20 and –40 mV, respectively. The CMDex‐MnONPs with 20 nm show antiferromagnetic behavior at room temperature, and the magnetic properties are found to be strongly dependent of the nanoparticle size, increasing the contribution of the ferromagnetic Mn₃O₄ phase with decreasing size for nanoparticles about 3 nm. Cytotoxicity evaluation in cancerous and noncancerous cells in the range of 5.0–50.0 μg mL^?1 shows low toxicity for cancerous cells and lack of the same for healthy cells lines. Related to the magnetic properties, CMDex‐MnONP presents significant r₁ relaxivity and low r₂/r₁ relaxivity ratio. The results suggest that these nanoparticles display characteristics for potential applications as an MRI T₁ contrast agent.     

Novel nanofluids based on mesoporous silica for enhanced heat transfer

Nanofluids, which are liquids with engineered nanometer-sized particles suspensions, have drawn remarkable attraction from the researchers because of their enormous potential to enhance the efficiency in heat-transfer fluids. In the present study, water-based calcined mesoporous silica nanofluids were prepared and characterized. The commercial mesoporous silica (MPSiO₂) nanoparticles were dispersed in deionized water by means of pH adjustment and ultrasonic agitation. MPSiO₂ nanoparticles were observed to have an average particle size of 350 ± 100 nm by SEM analysis. The concentration of MPSiO₂ was varied between 1 and 6 wt%. The physicochemical properties of nanofluids were characterized using various techniques, such as particle size analyzer, zeta-potential meter, TEM, and FT-IR. The thermal conductivity was measured by Transient Plane Source (TPS) method, and nanofluids showed a higher thermal conductivity than the base liquid for all the tested concentrations.     

Luminescence mechanism of acoustic and laser-induced cavitation

A new approach is proposed for explaining the experimental data on sonoluminescence of acoustic and laser-induced cavitation bubbles. It is suggested that two different sonoluminescence mechanisms, namely, thermal and electric ones, are possible and that they manifest themselves depending on the bubble dynamics. An intense thermal luminescence occurs as a result of compression of an individual stationary spherical bubble; a weak electric luminescence accompanies the deformation and splitting of the bubble when thermal luminescence is suppressed (for example, in the case of multibubble sonoluminescence). It is shown that, when an individual bubble loses its spherical shape under the effect of different actions (change in the acoustic pressure, artificial deformation, translatory motion, etc.) or when a laser-induced bubble undergoes fragmentation, the sonoluminescence spectrum exhibits specific bands that are similar to the bands in the multibubble sonoluminescence spectrum. The appearance of these bands is attributed to the suppression of the thermal sonoluminescence mechanism and the manifestation of the electric mechanism. It is shown that the maximum temperature T _max characterizing the compression of a laser-induced bubble is primarily determined by the temperature of the plasma at the instant of the laser-induced breakdown, whereas, for an acoustic bubble, T _max is primarily determined by the acoustic and hydrostatic pressures and by the saturation vapor pressure of the liquid.     

Multibubble sonoluminescence as a tool to study the mechanism of formic acid sonolysis

Sonoluminescence spectra collected from 0.1 to 3.0 M aqueous solutions of formic acid sparged with argon show the OH(A²Σ⁺−X²Π_i) and C₂(d³Π_g → a³Π_u) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C₂ Swan band. It is concluded that C₂ emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C₂ band is much stronger at high ultrasonic frequency compared to 20 kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative mechanism.     

圆锥气泡发光的光谱性质

在改进的U型管装置中观察到一种圆锥气泡声致发光现象。声致发光产生的单个光脉冲的能量可达到约1.4 毫焦. 脉冲宽度约100 毫秒。发光光谱由连续光谱上叠加C2,CN,和CH的激发态光谱构成。这种圆锥气泡声致发光为单泡声致发光和多泡声致发光提供了一种联系。     

Luminescence of Tb3+ and Gd3+ ions in sonolysis under the conditions of a single bubble moving in aqueous solutions of TbCl3 and GdCl3

Luminescence bands of Tb³⁺ and Gd³⁺ ions are detected during sonolysis in the regime of a moving single bubble in aqueous solutions of TbCl₃ and GdCl₃ salts with concentration 1–2 mol/L. Saturation with argon, low temperatures of solutions (?5°C), and a high concentration of salts are the factors facilitating sonoluminescence of the metal. Comparison with the characteristics of sonoluminescence of lanthanide ions studied earlier in the regimes of multibubble and single-bubble sonolysis with a stationary bubble shows that the electron excitation of metal ions in the given case is associated with translational displacements of the bubble. Our results confirm the validity of the sonochemical model of microdroplet injection, which explains the penetration of nonvolatile salts into cavitation bubbles as a result of their deformation during intense movements.