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.

Application of Sonotriboluminescence to Determine Arene Molecules in Hydrocarbons.

The sonotriboluminescence of suspensions of terbium(III) and europium(III) sulfates in decane without and in the presence of benzene, toluene and p-xylene was studied. The choice of crystals of these lanthanides is due to the fact that they have intense luminescence during mechanical action, and also do not dissolve in hydrocarbon solvents. During ultrasonic exposure to suspensions in pure alkanes, bands of Ln3+ ions and N2 in the UV region are recorded in the luminescence spectrum. When aromatic hydrocarbon molecules are added, bands of benzene, toluene and p-xylene molecules, coinciding with their photoluminescence spectra, are recorded in the sonotriboluminescence spectra in the UV region. The high sensitivity of the luminescence of suspensions to arene additives made it possible to obtain the dependence of the characteristic fluorescence of arene molecules in the sonotriboluminescence spectra on their concentration in suspensions. The limits of detection of benzene, toluene and p-xylene in the composition of this suspension were established. The lower limits of detection from the sonotriboluminescence spectra for xylene, toluene and benzene are 0.1, 3 and 50 ppmv, respectively. Fluorescence bands of these molecules were also recorded in the sonotriboluminescence spectra of suspensions in commercial dodecane and heptane with additives of commercial gasoline (up to 1%). The results obtained can be used for luminescent detection of aromatic compounds in saturated hydrocarbons.

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 (<50 nm) 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 396 nm 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 8.3·10-3 M. 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 ± 500 K.

Luminescence of Aromatic Compounds During Ultrasonic Treatment of Tb2(SO4)3 Suspension in Commercial Gasoline.

The spectral-luminescent properties of a suspension of terbium sulfate in commercial gasoline under sonication are studied. The following emitters are identified from the luminescence spectrum: *Tb3+ ions in crystals, electronically excited molecules of arenes (benzene, toluene, and xylenes), and polycyclic aromatic hydrocarbons (PAHs) in the liquid phase of the suspension. The study of sonotriboluminescence in gasoline-heptane and heptane-xylene-PAH synthetic mixtures shows for the first time that there is an effective luminescence activator in gasoline, that is, terphenyl molecules. It has been established that these molecules have the highest luminescence yield among all sonotriboluminescence emitters found. This is provided by the transfer of the excitation energy from monocyclic arene molecules primarily excited during the sonication. In this case, the primary excitation of aromatic hydrocarbon molecules in commercial gasoline during the ultrasonic treatment of suspensions occurs under the impact of charged particles/electrons generated during electrical discharges initiated by collision and destruction of microcrystals. This process is similar to radioluminescence excitation in liquid scintillators which can be considered commercial gasoline. The formation of *Tb3+ is due to separation and recombination processes of charges that populate the excited states of luminescence centers in microcrystals electrified during tribodestruction under sonication of the suspension.

Photoluminescence and mechanoluminescence of solid-state zirconocene dichlorides.

Spectral-luminescence properties of 23 samples of zirconium complexes were studied. Mechanoluminescence spectra of 10 complexes were obtained. The solid-state component of the mechanoluminescence spectrum, that is the luminescence of the crystal itself, coincided with the photoluminescence spectra of these complexes, which indicated identical emission from the same excited states in mechanoluminescence and photoluminescence, despite the different ways of excitation. The luminescence maximum was red shifted as substituents appeared in the ligand, in particular in the presence of a bridging group connecting π-ligands (ansa-complexes) and also for a substituted bis-indenyl complex rac-Me2 Si(2-Me-4-Ph-5-OMe-6-But -Ind)2 ZrCl2 ). It was found that mechanical destruction of the rac-isomer of complex Mе2 С(2-Me-4-But -C5 H2 )2 ZrCl2 , unlike that of the meso-isomer, was accompanied by a more than a 10-fold increase in intensity and by a shift in the mechanoluminescence spectrum to longer wavelengths.

New sonochemiluminescence involving solvated electron in Ce(III)/Ce(IV) solutions.

The moving single-bubble sonoluminescence of Ce3+ in water and ethylene glycol solutions of CeCl3 and (NH4)2Ce(NO3)6 was studied. As found, a significant part of intensity of the luminescence (100% with cerium concentration less than 10-4 M) is due to the sonochemiluminescence. A key reaction of sonochemiluminescence is the Ce4+ reduction by a solvated (or hydrated in water) electron: Ce4+ + es (eaq) â†’ *Ce3+. Solvated electrons are formed in a solution via electrons ejection from a low-temperature plasma periodically generated in deformable moving bubble at acoustic vibrations. Reactions of heterolytic dissociation of solvents make up the source of electrons in the plasma. In aqueous CeCl3 solutions, the Ce4+ ion is formed at the oxidation of Ce3+ by OH radical. The latter species originates from homolytic dissociation of water in the plasma of the bubble, also penetrating from the moving bubble into the solution. The sonochemiluminescence in cerium trichloride solutions are quenched by the Br- (acceptor of OH) and H+ ions (acceptor of eaq). In water and ethylene glycol solutions of (NH4)2Ce(NO3)6, the sonochemiluminescence also quenched by the H+ ion. The sonochemiluminescence in CeCl3 solutions is registered at [Ce3+] ≥ 10-5 M. Then the sonochemiluminescence intensity increases with the cerium ion concentration and reaches the saturation plateau at 10-2 M. It was shown that sonophotoluminescence (re-emission of light of bubble plasma emitters by cerium ions) also contributes to the luminescence of Ce3+ in solutions with [Ce3+] ≥ 10-4 M. If the cerium concentration is more than 10-2 M, a third source contributes to luminescence, viz., the collisional excitation of Ce3+ ions penetrating into the moving bubble.

Luminescence of aromatic hydrocarbon molecules in the sonication of terbium sulfate suspensions.

The sonication of terbium sulfate suspensions in benzene, toluene, and p-xylene induces intense UV luminescence (260-320 nm). The luminescence bands coincide with the fluorescence spectra of these aromatic hydrocarbons, but it is not observed in their sonoluminescence spectra. Furthermore, the spectra of ultrasound-initiated luminescence of the suspensions defined as sonotriboluminescence, which is 103 times more intense than the sonoluminescence of hydrocarbons, exhibit also emission from the ∗Tb3+ ion. The luminescence of ∗N2, which is observed during traditional triboluminescence of terbium sulfate in air, is hardly detectable in the case of sonolysis of terbium sulfate suspensions in aromatic hydrocarbons, but can be observed on decreasing the temperature of the suspensions, which decreases the saturated vapor pressure of the liquids. A possible mechanism of excitation of aromatic hydrocarbon molecules during sonotriboluminescence is discussed.

Mechanoluminescence of Ce/Tb inorganic salts in methane-acetylene mixtures with inert gases.

The mechanoluminescence of cerium (Ce) and terbium (Tb) lanthanide salts is studied in hydrocarbon [methane (CH4 ) and acetylene (C2 H2 )] and inert [helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe)] gaseous mixtures. The lines of *N2 , *Ln3+ , inert gases, *CH, and *C2 radicals resulted from the mechanochemical decomposition of CH4 and C2 H2 are observed in the emission spectrum. The luminescence intensity of the inert gases decreases with the hydrocarbon gas concentration in the mixture. The intensities of the *CH or *C2 bands remains almost unchanged within 15-100 vol% of CH4 or C2 H2 in the mixture. When the concentration of CH4 or C2 H2 is lower than 15%, the intensities of the CH or C2 bands increase achieving their maxima at 0.5-3% of the hydrocarbon. This is probably due to the optimal compositions of the mixtures with the most efficient generation of electrical discharges responsible for mechanoluminescence.