Computational simulation of ionization processes in single-bubble and multi-bubble sonoluminescence

The most recent spectroscopic studies of moving-single bubble sonoluminescence (MSBSL) and multi-bubble sonoluminescence (MBSL) have revealed that hydrated electrons (e$_{{\rm aq}}^{-}$) are generated in MSBSL but absent in MBSL. To explore the mechanism of this phenomenon, we numerically simulate the ionization processes in single- and multi-bubble sonoluminescence in aqueous solution of terbium chloride (TbCl$_{3}$). The results show that the maximum degree of ionization of single-bubble sonoluminescence (SBSL) is approximately 10000 times greater than that of MBSL under certain special physical parameters. The hydrated electrons (e$_{{{\rm aq}}}^{-}$) formed in SBSL are far more than those in MBSL provided these electrons are ejected from a bubble into a liquid. Therefore, the quenching of e$_{{{\rm aq}}}^{-}$ to SBSL spectrum is stronger than that of the MBSL spectrum. This may be the reason that the trivalent terbium [Tb(III)] ion line intensities from SBSL in the TbCl$_{3}$ aqueous solutions with the acceptor of e$_{{{\rm aq}}}^{-}$ are stronger than those of TbCl$_{3}$ aqueous solutions without the acceptor of e$_{{{\rm aq}}}^{-}$. Whereas the Tb(III) ion line intensities from MBSL are not variational, which is significant for exploring the mechanism behind the cavitation and sonoluminescence.     

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.     

Theory of light emission in sonoluminescence based upon transitions in confined atoms

A theory of light emission in sonoluminescing hydrogen bubbles, based upon transitions in confined atoms, is proposed. Despite the simplicity of the assumptions this model accounts for a number of facts related to sonoluminescence: a broadband spectrum in the correct wavelength window is predicted as well as the number of emitted photons. Taking the temperature at the moment of collapse as a parameter we argue that confined atomic transitions at 4000 K may account for the observed light emission. This result favours a ‘cold’ interpretation of sonoluminescence in contrast to previous theories. Many considerations are qualitatively extendible to rare gases.     

Conical bubble photoluminescence from rhodamine 6G in 1, 2-propanediol

A modified U-tube conical bubble sonoluminescence device is used to study the conical bubble photoluminescence. The spectra of conical bubble sonoluminescence at different concentrations of rhodamine 6G (Rh6G) solution in 1,2-propanediol have been measured. Results show that the sonoluminescence from the conical bubbles can directly excite Rh6G, which in turn can fluoresce. The light emission of this kind is referred to as conical bubble photoluminescence. The maximum of fluorescence spectral line intensity in the conical bubble photoluminescence has a red shift in relative to that of the standard photo-excited fluorescence, which is due to the higher self-absorption of Rh6G, and the spectral line of conical bubble photoluminescence is broadened in width compared with that of photo-excited fluorescence.     

Opacity and transport measurements reveal that dilute plasma models of sonoluminescence are not valid

A strong interaction between a nanosecond laser and a 70?μm radius sonoluminescing plasma is achieved. The overall response of the system results in a factor of 2 increase in temperature as determined by its spectrum. Images of the interaction reveal that light energy is absorbed and trapped in a region smaller than the sonoluminescence emitting region of the bubble for over 100?ns. We interpret this opacity and transport measurement as demonstrating that sonoluminescencing bubbles can be 1000 times more opaque than what follows from the Saha equation of statistical mechanics in the ideal plasma limit. To address this discrepancy, we suggest that the effects of strong Coulomb interactions are an essential component of a first principles theory of sonoluminescence.     

稀土盐水溶液单泡声致发光中的特征光谱

在溶有稀有气体的稀土盐氯化铽水溶液中进行了单泡声致发光光谱的研究. 在固定驱动超声频率、不同驱动声压下, 观察到了一系列OH自由基从第一激发态A²∑⁺到基态X²Π 各振动能级跃迁所产生的谱线, 包括波长307 nm处的(0, 0)跃迁谱线, 335 nm处的(0, 1)跃迁谱线以及276 nm处的(1, 0) 跃迁谱线等. 实验结果表明较高的驱动声压有利于 276 nm处谱线的产生, 而较低的驱动声压则有利于 307 与 335 nm 处谱线的产生. 通过定义线状光谱与连续谱的光强比, 定量地表征了线状光谱在总光谱中的相对强度, 并给出了驱动声压对各跃迁谱线光强比的影响. 关键词： 单泡声致发光 驱动声压 线状光谱 光强比     

声致发光的流体动力学实验方法

介绍两种使用流体动力学实现声致发光的方法:刹管法和U管圆锥泡法.这两种方法的设备简单,操作方便,容易在普通物理实验中进行,所得结果和传统单泡声致发光有所不同.U管圆锥泡法创造了发光功率和单脉冲能量的新记录,并首次用条纹相机得到了时间分辨发射光谱.     

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.     

Sonoluminescence from a single bubble driven at 1 megahertz

Measurements of the spectrum of sonoluminescence from an isolated bubble driven at 1 MHz are well fit by assuming thermal bremsstrahlung from a transparent 10(6) degree plasma. According to this interpretation, the photon-matter mean free path is larger than the light-emitting radius of a 1 MHz bubble, but smaller than the light-emitting radius for bubbles driven at approximately 40 kHz, thus accounting for the observed blackbody spectrum at 40 kHz.     

Temperature and Pressure inside Sonoluminescencing Bubbles Based on Asymmetric Overlapping Sodium Doublet

We experimentally measure the sodium D-lines from the multibubble sonoluminescence in sodium hydroxide aqueous solution. The asymmetric overlapping D-lines are successfully decomposed based on the Fourier transform analysis. The line broadening of the decomposed sodium D-lines shows the effective temperature of 3600-4500 K and the pressure of 560-1000 atm during sonoluminescence.     

Measurements of the dependence of sonoluminescence on acoustic pressure of ultrasonic field and measurements of the acoustic spectrum of cavitation noise

Time-averaged values of the sonoluminescence in dependence on the acoustic pressure of ultrasonic field were measured in distilled water, exposed to ultrasonic field of frequency 43·40 kHz at temperatures of 5, 15, 25, 35 and 45 ° C in ambient atmospheric pressure. Average values of the sonoluminescence were measured with the aid of a photomultiplier — as a voltage drop on its working resistance. Effective acoustic pressure of ultrasonic field was measured with a piezoelectric s ensor coupled to a high-frequency millivoltmeter. The acoustic spectrum of cavitation noise (from 0·3 up to 2·0 MHz) in water was measured at temperatures of 5, 15, 25, 35 and 45 °C for various mean values of the sonoluminescence. Piezoelectric sensor was employed in detecting the spectrum of cavitation noise. The voltage signal on the sensor was measured by means of a heterodyne voltmeter. Sonoluminescence flashes were detected with a photomultiplier, amplified and displayed on an oscillograph screen together with the intensity of ultrasonic field in the liquid. Theoretical arguments are outlined explaining the occurrence of maxima in the acoustic spectrum of the cavitation noise.The authors express their thanks to Prof. RNDr. M.Brdika for his constant interest in their work and useful hints.     

乙二醇溶液中圆锥泡声致发光的发光特性

利用一种改进后的U形管圆锥泡声致发光装置，研究了乙二醇溶液中圆锥泡声致发光的发光特性.实验结果表明，利用乙二醇溶液可以得到超强的单个发光脉冲，其脉冲宽度可以达到150 μs，其值远远高于其他方式产生的声致发光的脉冲宽度.测量得到的光谱为一从紫外到可见光波长范围的连续谱，在589 nm附近叠加有钠的3P-3S原子发射谱线.在钠的原子发射谱线两侧测量得到了Na-Ar分子激发态跃迁形成的蓝卫星带，并在声致发光实验中测得了Na-Ar的红卫星带以及钠的3S-4S原子发射谱线. 关键词： 圆锥泡声致发光 光脉冲 光谱 卫星带     

Influence of dissolved oxygen content on multibubble sonoluminescence with ambient-pressure reduction

The efficiency of chemical reactions in the presence of ultrasound at reduced pressures has been monitored using the influence of dissolved oxygen (DO) content on a luminol solution undergoing multibubble sonoluminescence. From these measurements under the condition of constant ultrasonic frequency and constant amplitude of sound pressure, it is shown that the intensity of sonoluminescence is higher at subatmospheric ambient pressure than at atmospheric pressure under the same degree of saturation. Also, it is found that there is an appropriate content of DO to produce the highest intensity of the luminescence and its value varies with ambient pressure.     

Determination of Lifetime of Ce3+ Luminescence by Time-Correlated Single Photon Counting Method during Sonoluminescence from Aqueous CeCl3 Solution

Optics and Spectroscopy - Using a counter for single photon correlations, the flashes of sonoluminescence and sonophotoluminescence of a 0.1 M aqueous solution of CeCl3 are separated by time. The...     

Inverse effects of the gas feed positioning on sonochemistry and sonoluminescence

Purging of solutions to enhance sonochemical reactions is a common practice. A fundamental study combining sonoluminescence spectroscopy and sonochemical activity is adopted to study the effects of continuous Ar gas flow in the solution and of the position of the gas inlet tube on high-frequency sonolysis of aqueous solutions. It has been observed that neither sonochemical activity nor sonoluminescence intensity is controlled by the gas solubility only. Besides, the change in position of the gas inlet tube leads to opposite effects in sonoluminescence intensity and sonochemical activity: while the former increases, the latter decreases. Such an observation has never been reported despite sonochemical reactions have been carried out under different gas environments. Sonoluminescence spectroscopy indicates that more extreme conditions are reached at collapse with the gas inlet on the side, which could be explained by a more symmetrical collapse. Finally, it is shown in certain conditions that it is possible to favor the formation of some sonochemical products simply by positioning the gas inlet at different positions, which has practical significance in designing large scale sonochemical reactors for industrial applications.     

Activation of TiO2 photocatalyst by single-bubble sonoluminescence for water treatment

Single-bubble sonoluminescence (SBSL) continues to attract many researchers because the physics behind it remains uncertain and few applications have appeared. In this study, we propose to apply SBSL to a water-treatment technique. The SBSL flashes contain intense ultraviolet light, which activates a TiO2 photocatalyst to decompose organic compounds in water. This mechanism comes from the similar spectrum patterns between SBSL emission and TiO2 absorption. SBSL in solutions containing small amount of TiO2 powder decomposed phenol and 2,4-dinitrophenol with efficiency several times higher than those by the existing methods.     

Multibubble sonoluminescence pulses from Na atoms in viscous liquid

Multibubble sonoluminescence pulses of Na and continuum emissions were measured from NaCl-ethylene glycol solution saturated with Xe at 28 kHz. The Na emission consisted of multiple-peak pulses and single pulses. The intrinsic pulse width estimated from single pulses was 0.37 ns, which differs from 10-165 ns obtained by previous work. High-speed shadowgraphs of bubble dynamics and high-speed movies (32000 fps) of sonoluminescence were observed. The observations suggest that the multiple-peak pulse is due to the superposition of single peaks resulting from bubbles fragmented from a characteristic bubble which repeats the fragmentation and coalescence. This phenomenon may be specific to viscous liquids.     

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.     

Spectrum of luminescence from laser-created bubbles in water

The spectrum of the luminescence emitted at the collapse of single laser-induced bubbles in water is measured for different maximum bubble radii. Bubbles as large as 2 mm show a molecular OH(*) band at 310 nm in the spectrum, which otherwise can be fitted approximately with a blackbody curve at a temperature of 7800 K. This finding provides a connection between the light emission of single bubbles and multibubble sonoluminescence, since in the latter case the same molecular band is observed. Surface instabilities are observed in the larger bubbles, and may be connected with the OH(*) emission.     

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