Single Bubble Sonoluminescence Research Articles

Single-bubble sonoluminescence of itterbium(II or III) and thulium(II or III) chloride nanoparticles colloidal suspensions in dodecane

Colloidal suspensions of nanoparticles of di- and trivalent ytterbium and thulium chloride crystals in dodecane were prepared by ultrasonic dispersion. The average nanoparticle size in the suspensions was 20–35 nm. During single-bubble sonolysis with the bubble moving at the standing wave antinode, identical bands with a maximum at 550 nm appeared in the sonoluminescence spectra with spectral resolution Δλ = 15 nm for suspensions of both Yb(II) and Yb(III) salts. Bands with a maximum at 600 nm were found for suspensions of Tm(II) and Tm(III) salts. These sonoluminescence bands coincide with the photoluminescence bands of Yb(II) (550 nm) or Tm(II) (600 nm) salts, respectively. For suspensions of divalent lanthanide salts, these sonoluminescence bands appear when nanoparticles get into a moving bubble, because of collisional excitation of Yb(II) or Tm(II) in the bubble plasma, which periodically appears during acoustic oscillations: [Ln(II)]suspension → [Ln(II)]bubble → [Ln(II)]plasma → [Ln(II)*]plasma → Ln(II) + hνLn(II). The presence of analogous bands for suspensions of trivalent lanthanide salts is caused, in particular, by also their reduction in the plasma after they get into a bubble: [Ln(III)]suspension → [Ln(III)]bubble → [Ln(III)]plasma → [Ln(II), Ln(II)*]plasma → [Ln(II)*]plasma → Ln(II) + hνLn(II). The reduction of lanthanide ions in the bubble plasma is not limited to the reaction Ln(III) → Ln(II), Ln(II)*, but can proceed further giving singly charged lanthanide cations and lanthanide atoms: Ln(II) → Ln(I), Ln(I)* → Ln(0), Ln(0)*. The single-bubble sonoluminescence spectra with Δλ = 1.5 nm for a suspension of Yb(III) salt showed characteristic lines of Yb(I) and Yb(0). These characteristic lines and bands for ytterbium and thulium atoms and ions are suitable for sonoluminescent spectroscopic analysis, that is, identification and quantification of ions in solutions and suspensions and determination of electronic temperature in bubble plasma.

About the sonoluminescent spectral portrait of gasoline water pollution

Single-bubble sonoluminescence spectra of the following samples were recorded in the modes of standing and moving bubble in liquid near the center of its levitation under the action of ultrasound: water contaminated with additives of commercial gasoline (1.5 – 38 mg·L−1), water with additives of individual gasoline components (hexane, benzene, toluene, p-xylene, naphthalene, anthracene, and p-terphenyl), and solutions of these gasoline components in hexane. Characteristic bands λmax of gasoline component emitters are recorded in the sonoluminescence spectra of a moving bubble for water samples contaminated with additives of commercial gasoline: 290 (p-xylene), 340 (p-terphenyl), 381, 399, 424, 449 (anthracene), and 438, 474, 516, 564 nm (C2, a hydrocarbon decomposition product during sonolysis).These bands are as a spectral portrait of gasoline contamination of water: they make it possible to identify gasoline in water in the above mentioned range of its content and to find a quantitative content of individual gasoline components.

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R≃0.8μm , and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.

Vapor compression and energy dissipation in a collapsing laser-induced bubble

The composition of the gaseous phase of cavitation bubbles and its role on the collapse remains to date poorly understood. In this work, experiments of single cavitation bubbles in aqueous ammonia serve as a novel approach to investigate the effect of the vapor contained in a bubble on its collapse. We find that the higher vapor pressure of more concentrated aqueous ammonia acts as a resistance to the collapse, reducing the total energy dissipation. In line with visual observation, acoustic measurements, and luminescence recordings, it is also observed that higher vapor pressures contribute to a more spherical collapse, likely hindering the growth of interface instabilities by decreasing the collapse velocities and accelerations. Remarkably, we evidence a strong difference between the effective damping and the energy of the shock emission, suggesting that the latter is not the dominant dissipation mechanism at collapse as predicted from classical correction models accounting for slightly compressible liquids. Furthermore, our results suggest that the vapor inside collapsing bubbles gets compressed, consistently with previous studies performed in the context of single bubble sonoluminescence, addressing the question about the ability of vapors to readily condense during a bubble collapse in similar regimes. These findings provide insight into the identification of the influence of the bubble content and the energy exchanges of the bubble with its surrounding media, eventually paving the way to a more efficient use of cavitation in engineering and biomedical applications.

Single-Bubble Sonoluminescence of Colloidal Suspensions of Europium(II) Salt Nanoparticles.

Colloidal suspensions of EuCl2, EuBr2, and EuSO4 nanoparticles (<50 nm) in dodecane and EuSO4 in 70% H2SO4 were synthesized. Moving single-bubble sonoluminescence (m-SBSL) spectra were obtained for a bubble performing radial oscillations in these suspensions and translational motions at the antinode of a standing ultrasonic wave with a frequency of about 27 kHz. In these spectra (at a spectral resolution of 10 nm), the sono-excited luminescence bands of the Eu2+ ion were detected for the first time, coinciding in the shape and position of the maxima (404, 413, and 377 nm for EuCl2, EuBr2, and EuSO4, respectively) with the bands of Eu2+ located in a crystalline environment in the photoluminescence spectra of nanoparticles of europium salts in suspensions. The detected sonoluminescence of Eu2+ arises due to the injection of nanoparticles into a bubble deformed during motion and excitation of a lanthanide ion at the periphery of the bubble volume during collisions of nanoparticles with charged particles, mainly electrons, coming from a hot nonequilibrium plasma, which periodically arises during bubble compression. Evidence for the excitation of the europium ion in the bubble is the absence of its luminescence bands in the SBSL spectra of the translationally immobile bubble, in which nanoparticles are unlikely to enter. The nanoparticles that enter the bubble also undergo decomposition in the plasma into fragments, in particular, with the formation of Eu, Eu+ in the excited state. The atomic lines of these fragments were recorded for the first time in the m-SBSL spectrum with a resolution of 1 nm for a suspension of EuSO4 nanoparticles in 70% H2SO4. The resulting m-SBSL spectra will add to the library of characteristic spectra of objects of sonoluminescent spectroscopic analysis and will make it possible to identify and determine the content of Eu or Eu2+ in these objects.

Ubiquitous fullerenes: A detection of C60 and C70 under sonolysis of aqueous graphite colloidal suspensions

For the first time, the molecular bands of the C2 species were detected in the single-bubble sonoluminescence spectra of aqueous colloidal suspensions of graphite nanoparticles (≤ 50 nm) obtained by ultrasonic dispergation upon multi-bubble sonolysis. The registration of these bands indicates that graphite nanoparticles enter the moving cavitation bubble together with solution microdroplets, where they are decomposed in the nonequilibrium plasma that occurs during ultrasonic vibrations into small fragments, including C2 radicals. Based on the conventional mechanism for the formation of fullerenes at the arc-discharge synthesis, starting from C2, under plasma conditions, we suggest that these framework molecules are synthesized in a cavitation bubble during single-bubble sonolysis of graphite nanoparticles. Indeed, the presence of the C60 and C70 fullerenes was registered in the accumulated sonolysis products of samples of suspensions of graphite nanoparticles with the chromatographic and mass-spectrometric techniques.

О ВЫХОДАХ ВОЗБУЖДЕНИЯ И ЛЮМИНЕСЦЕНЦИИ ТРЕХВАЛЕНТНЫХ ИОНОВ ЛАНТАНИДОВ ПРИ ОДНОПУЗЫРЬКОВОМ СОНОЛИЗЕ РАСТВОРОВ В СЕРНОЙ КИСЛОТЕ

The light yields of luminescence (Glum) and the yields of excited ion production (yields of excitation, Gext) were measured for the first time for a number of trivalent lanthanide ions (Ln3+) during moving single-bubble sonoluminescence in solutions of 10-2 M Ln3+ in 70% H2SO4. The luminescence yields were determined by comparing the integrated sonoluminescence intensity of the test solution with the radioluminescence intensity of the reference light source, and the excitation yields were found from the relation Gext = Glum/φ, where φ are the photoluminescence quantum yields of Ln3+ ions in the solution, which were also measured experimentally in the work. Determined yields Glum = (0.63, 0.96, 1.8, 5.1, 0.49)´107 photon/100 eV and Gext = (0.066, 1.6, 0.7, 1.5, 0.7)´108 excited ions/100 eV for Ce3+, Eu3+, Gd3+, Tb3+ ions, Dy3+, respectively. It was confirmed that, as previously shown in the case of radiation-excited luminescence of lanthanide ions (Kazakov V.P., Sharipov G.L. Radioluminescence of aqueous solutions. M.: Nauka, 1986. p. 116), transition with a change in the principal quantum number (4f→5d, Ce3+ ion) is an order of magnitude or less lower than the excitation yield in a transition without its change (4f→4f, Eu3+, Tb3+ , and others ions).

Single-bubble sonoluminescence of aqueous suspensions of ZnS or Tb(acac)3·H2O nanoparticles

Aqueous suspensions of nanoparticles (below 50 nm in size) of ZnS or Tb(acac)3·H2O crystals were prepared by dispersion under multibubble sonolysis. Single-bubble sonoluminescence (SL) of these colloidal suspensions in an ultrasonic standing wave was found. For a ZnS suspension, the SL spectrum of a bubble moving at acoustic pressure pa = 1.29 bar, recorded with 12 nm resolution, exhibited a ZnS band with a maximum at 470 nm against the background of a wide continuum of bubble luminescence (200–700 nm). At a resolution of 1.2 nm, numerous lines of atomic (Zn, S) and ionic (S+, S2+, S3+) emitters were present in the 270–670 nm range. For a Tb(acac)3 suspension at 12 nm resolution, Tb3+ quasilines were detected at 488, 544, 585, and 618 nm (5D4 – 7Fj transitions, j = 6,5,4,3). At 1.2 nm resolution, no terbium atomic lines were found. The ZnS band and Tb3+ quasilines were present, although with a lower intensity (at a constant continuum intensity), in the SL spectra of suspensions for a stationary (pa = 1.07 bar) bubble. The atomic emitter lines for a stationary bubble were absent in the spectra of both suspensions. The ZnS band and Tb3+ quasilines in the SL spectra were similar to those in the photoluminescence (PL) spectra. However, the spectrum of a moving bubble in a Tb(acac)3 suspension differed from the PL spectrum in the relative intensities of the quasilines for some transitions. It was concluded that a non-equilibrium plasma was ignited in a stationary or moving bubble in suspensions under periodic compression of its gas content. This was the main source of luminescence during sonolysis, which was observed as thermal emission bursts in a plasma with a spectral continuum. In addition, sonophotoluminescence was generated as re-emission of the continuum luminescence partially absorbed by nanoparticles in suspensions; this occurred as flashes of ZnS or Tb3+ characteristic luminescence. Additionally, for a moving bubble, there was luminescence of these emitters associated with the entry of nanoparticles into the bubble and the collisional excitation of emitters in the plasma. In the case of a ZnS suspension, there was luminescence of atomic emitters (Zn, S) that formed upon decomposition and excitation of fragments of the initial emitter (ZnS) in a bubble plasma. The absence of a similar component in the SL spectrum of the Tb(acac)3 suspension may be attributable to low efficiency of the collisional excitation of terbium atoms, which were undoubtedly formed upon decomposition of nanoparticles in a bubble plasma. The emitters and mechanisms of the studied single-bubble sonoluminescence in colloidal suspensions were compared with those for the previously considered (J. Luminescence. 252 (2022) 119389) multibubble sonotriboluminescence in non-colloidal suspensions of ZnS or Tb(acac)3·H2O crystals.

The effect of bulk viscosity on single bubble dynamics and sonoluminescence

In our previous paper, we derived a new single bubble model including the effect of bulk viscosity. To confront it to experiments, single bubble dynamics was measured here in 30% (v/v) glycerol-water mixture under different acoustic amplitudes and compared to models including or not the effect of bulk viscosity. The results showed that calculated bubble dynamics were not significantly affected by the bulk viscosity within the experimental conditions used in this study. However, there was a noticeable delay for the first rebound when bulk viscosity was considered. The corresponding sonoluminescence intensities were collected and compared with theoretical predictions. The results did not allow to discriminate between the two models (one includes the effect of bulk viscosity, the other does not), confirming the negligible effect of bulk viscosity in this condition (30% (v/v) glycerol-water mixture). Due to the instability of a single bubble in higher viscosity solutions, we could not implement experiments that can discriminate between the two models.

Single-Bubble Sonoluminescence of Colloidal Suspensions as a New Technique for Sonoluminescent Spectroscopic Analysis.

This is a brief research review on the new method of development for element luminescence determination, namely, sonoluminescent spectroscopy. The advantages and disadvantages of the technique of multibubble sonoluminescence (MBSL) in solutions used to apply this method are discussed. It has been shown that the use of a new technique moving single-bubble sonoluminescence (m-SBSL) in colloidal suspensions of nanoparticles (<50nm) containing the elements analyzed seems preferable for this purpose. This makes it possible to determine elements not only at lower concentrations than when using MBSL in solutions but also to find elements that are unavailable for determination through previous techniques. Thus, this new technique expands the range of elements that can be determined using sonoluminescent spectroscopy. The article provides a detailed description of the standard procedure for the preparation and recording of m-SBSL in colloidal suspensions, as well as examples of characteristic spectra of some elements obtained and recorded for the first time according to this new technique (Al, K, Mn, Cd, Pt, Ni, and Ti), including those not previously found using the MBSL in solutions (Al, Cd, Pt, Ni, and Ti). An example of the analytical line at 396nm in the Al spectrum obtained through this new technique on the basis of an AlCl3 initial aqueous solution, the region of the linear dependence of the intensity on the AlCl3 concentration was registered, and the lower limit of the spectroscopic determination of the Al content in this solution was estimated as 8.3·10-3M. Using the analysis of the obtained Cd spectrum as an example, we carried out a spectroscopic measurement of the electronic temperature achieved at m-SBSL in bubble plasma at the moment of greatest compression of a bubble with light emission during its acoustic oscillations in dodecane, Te = 7900 ± 500K.

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 () 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 (TbCl3). 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 () 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 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 TbCl3 aqueous solutions with the acceptor of are stronger than those of TbCl3 aqueous solutions without the acceptor of . Whereas the Tb(III) ion line intensities from MBSL are not variational, which is significant for exploring the mechanism behind the cavitation and sonoluminescence.

Generation of excited Sm2+ ion and luminescence during sonochemical reduction of Sm3+ by solvated electron

Spectra of moving single-bubble sonoluminescence have been obtained for trichloride solutions of Sm, Tm and Yb in water and ethylene glycol. In addition to continuum solvent, the spectrum of Sm3+ salt in ethylene glycol contains a wide luminescence maximum at 754 nm. This maximum is related to 4f55d → 4f6 radiative transition *Sm2+ → Sm2+ + hν. Based on the analysis of available data on the nature of sonoluminescence of different lanthanide ions and the influence of the H+ electron acceptor on it, it is concluded that *Sm2+ formed by reduction of Sm3+ by electron solvated in ethylene glycol. The latter is generated during the solvent sonolysis. The formation and sonochemiluminescence of *Tm2+ and *Yb2+ under the same conditions of sonolysis was not found. Analysis of published literature shows that this new discovered example of generation and light emission of *Men + metal ion upon reduction of Me(n+1)+ by solvated electron, apparently, is a general phenomenon for transition metals if the reduction reaction energy is sufficient for electronic excitation of Men+.

Atomic luminescence of Ag during single-bubble sonolysis of silver nanoparticles aqueous suspension

For the first time, luminescence of Ag atoms was recorded during moving single-bubble sonolysis of silver nanoparticles aqueous colloidal suspension. This glow is caused by the entry of nanoparticles into a bubble deformable during motion and their decomposition to atoms with collisional excitation in the nonequilibrium plasma of the bubble. Nanoparticles were obtained by multibubble sonolysis of an AgNO3 solution with the addition of honey. This method was used to synthesize a stable suspension of Ag nanoparticles with an average size of ~ 10 nm. By comparing the experimental spectrum of this suspension and simulated spectra of Ag, the electron temperature in the bubble plasma was found to be ~ 10 000 K. Keywords: single-bubble sonoluminescence, silver nanoparticles, electron plasma temperature.

Atomic single bubble sonoluminescence of ytterbium in a colloidal suspension

For the first time, atomic single-bubble sonoluminescence of Yb in a colloidal suspension in dodecane of SiO2 nanoparticles containing YbCl3 was recorded. A spectrum was obtained containing Yb, Yb+ lines in the region of 300-550 nm, together with SiO lines, due to the entry of nanoparticles into the bubble during sonolysis of the suspension. The lower limit of determination of ytterbium in the initial aqueous solution of YbCl3 used for depositing onto nanoparticles, according to the intensity of the analytical line at 399 nm in this spectrum, is 3·10-3 mol/l. By comparing the experimental and temperature-dependent calculated spectra of ytterbium, we found the electronic temperature in the nonequilibrium plasma that arises during bubble collapse, where Yb atoms emit light: Te=7000± 500 K. Keywords: single-bubble sonoluminescence, silicon dioxide, ytterbium, colloidal suspension.

Атомарная однопузырьковая сонолюминесценция иттербия в коллоидной суспензии

For the first time, atomic single-bubble sonoluminescence of Yb in a colloidal suspension in dodecane of SiO2 nanoparticles containing YbCl3 was recorded. A spectrum was obtained containing Yb, Yb+ lines in the region of 300-550 nm, together with SiO lines, due to the entry of nanoparticles into the bubble during sonolysis of the suspension. The lower limit of determination of ytterbium in the initial aqueous solution of YbCl3 used for depositing onto nanoparticles, according to the intensity of the analytical line at 399 nm in this spectrum, is 3∙10–3 mol/l. By comparing the experimental and temperature-dependent calculated spectra of ytterbium, we found the electron temperature in the nonequilibrium plasma that arises during bubble collapse, where Yb atoms emit light: Te = 7000±500 K.

АКТИВАЦИЯ ОДНОПУЗЫРЬКОВОЙ СОНОЛЮМИНЕСЦЕНЦИИ И РАДИОЛЮМИНЕСЦЕНЦИИ ИОНОВ GD3+ И DY3+ АКЦЕПТОРАМИ ЭЛЕКТРОНА В ВОДНЫХ РАСТВОРАХ КАК СЛЕДСТВИЕ ГЕНЕРАЦИИ ГИДРАТИРОВАННОГО ЭЛЕКТРОНА ПРИ СОНОЛИЗЕ И РАДИОЛИЗЕ ВОДЫ

Discovered the activation of moving single-bubble sonoluminescence and radioluminescence for Gd3+ and Dy3+ ions in aqueous solutions of GdCl3 and DyCl3 by the acceptor of a hydrated electron (eaq-): H+, Cd2+, etc. This activation is similar to the previously found activation by acceptors of eaq- radioluminescence and single-bubble sonoluminescence for the Tb3+ ion. Electron acceptors do not affect the quantum yield of the said lantha-nide ions photoluminescence. They also do not affect the yield of their multibubble sonoluminescence in aqueous solutions, since eaqdoes not appear in significant amounts during multibubble sonolysis. The found luminescence activation effects of lanthanide ions are interpreted as a consequence of the suppression of the quenching (reduction) reactions of these electronically excited ions eaq: *Ln3+ + eaq- → Ln2+ by acceptors. The feasibility of these reactions was predicted for all Ln3+ ions based on a theoretical estimate of their free energy. The discovery of the described effects of activation of the luminescence of Ln3+ ions is a consequence and serves as confirmation of not only the known generation of eaq- during radiolysis, but also its previously unknown generation during moving single-bubble sonolysis of water.

Single-bubble sonoluminescence of suspensions in dodecane of porous SiO2 nanoparticles with lanthanide ions

Single-bubble sonoluminescence of colloidal suspensions in dodecane of SiO2 nanoparticles containing Ln3+ ions (Ce3+, Pr3+, Gd3+, Tb3+) was investigated. Sonoluminescence is achieved by irradiating the suspension with ultrasound (27 kHz) in a spherical standing-wave resonator. As found for all suspensions, the luminescence spectra of an immobile bubble contains a structureless continuum with no characteristic bands or Ln3+ lines, which is associated with the low probability of nanoparticle penetration into the bubble. For suspensions with Tb3+ or Gd3+ ions, the narrow bands (quasi-lines of f-f transitions) of these ions are recorded in the spectra of a bubble moving near the resonator’s centre. This is due to the entry of nanoparticles with Ln3+ ions into a bubble deformed during the motion and collisional electronic excitation of these ions in nonequilibrium bubble plasma. For suspensions with Ce3+ or Pr3+ ions, in the moving single-bubble sonoluminescence spectra, the bands corresponding to luminescent d-f transitions of these ions were not found despite their entry into the bubble similar to that of Tb3+ and Gd3+. This result is explained by much lower probability of collisional excitation during the electronic intershell 4f-5d transition in Ln3+ ions compared to the probability of such excitation upon the intrashell 4f-4f transition.

Turning single bubble sonoluminescence from blue in pure water to green by adding trace amount of carbon nanodots

Sonoluminescence (SL) is an interesting physical effect which can convert acoustic energy into light pulses. Up to now, the microscopic mechanism of the SL has not yet been fully clear. It is known that hydroxyl radicals play the important role for SL from water. In this work, we take advantage of carbon nano-dots (CNDs) as free radical captors to modulate the hydroxyl radicals (OH) in SL effect. Through studying the single bubble SL (SBSL) from CND aqueous solution (CNDAS) with trace amount of CNDs, we find that the color of SBSL is tuned dramatically from blue in water to green in CNDAS. Two different SL mechanisms can be identified from emission spectrum. One comes from blackbody-like radiation and another is attributed from the characteristic emission with identified peaks. The decrease in the yield of H2O2 in the presence of CNDs suggests the modulation effect on SL via OH interacting with CNDs. By comparison of the CNDs before and after sonication, it is found that hydroxyl radicals generated during SL can take part in the chain-like oxidation of the chemical groups attached to the CNDs to form larger amount of carboxyl groups. The blackbody temperature of blackbody-like radiation decreases from 15,600 K in water to 11,300 K in CNDAS. Moreover, the emission from hydroxyl radicals and two new luminescent centers related to carboxyl groups are introduced in SL from CNDAS. These important and interesting findings indicate that by adding trace amount of CNDs in water, the effect of SBSL can be significantly modulated, which can provide a macroscopic phenomenon for gaining an insight into the microscopic mechanism of the SL effect.

Sonoluminescence in solutions of organic aromatic luminophores: Monomer and excimer luminescence of benzene, toluene and p-xylene

This paper considers the spectra of glow that emerges during the sonolysis of benzene, toluene and p-xylene solutions in ethylene glycol under the action of a translationally motionless bubble levitating in the ultrasonic standing wave with a frequency of ~27 kHz or a moving bubble (single-bubble, or moving single-bubble sonoluminescence, SBSL, or m-SBSL, respectively). The m-SBSL spectra against the background of the broadband solvent continuum demonstrate the presence of characteristic luminescence bands of luminophores in the range of 270–305 nm (singlet excited monomers) and a band of singlet excited dimers (excimers) of these molecules with a maximum of 320 nm at a luminophores concentration in solution being 10−3-10−2 M. For 1.25∙10−3 M benzene solution, there were also recorded the bands of СН and С2 radicals occurred as a result of decomposing this luminophore. At concentrations higher than 10−2 M, luminophores luminescence is quenched and the m-SBSL spectra reveal only the continuum, the intensity of which also decreases with an increase in the luminophores concentration. This continuum is recorded without any significant change in its shape and intensity, with no bands of luminophores and radicals for the luminophores concentrations specified, and during SBSL. The obtained data are indicative of the penetration of luminophores molecules, in the m-SBSL regime, from the solution into the moving and deformed bubble according to the known sonochemical mechanism to inject solution nanodroplets and also their further collisional excitation in the nonequilibrium intrabubble plasma which repeatedly formed during oscillations of bubble in the acoustic field. The nonequilibrium plasma state determines the presence of luminescence both luminophore molecules (gas temperature about 103 K or less) and radical products of their decomposition (gas temperature is thousands K).

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 aq − ) are generated in MSBSL but absent in MBSL. To explore the mechanism this phenomenon, we numerically simulated the ionization processes in single- and multi-bubble sonoluminescence in aqueous solution of terbium chloride (TbCl3). 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 aq − ) formed in SBSL are far greater than those in MBSL provided these electrons are ejected from a bubble into a liquid. Therefore, the quenching of e 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 aq − are stronger than those of TbCl3 aqueous solutions without the acceptor of e aq − , whereas the Tb(III) ion line intensities from MBSL are not variational.