Effect of argon on the multibubble sonoluminescence of cerium, terbium, and dysprosium trichlorides

Abstract

The ultrasonic (20 kHz) multibubble sonoluminescence spectra of aqueous air or argon saturated solutions of CeCl 3 , TbCl 3 , and DyCl 3 were obtained. Saturation with argon leads to the intensity redistribution in the spectrum of the continuum with an increase in its short wavelength part and increases the intensity of the characteristic emission of Ce 3+ and Tb 3+ due to the enhancement of the sonophotoluminescence intensity, i.e., the re emission of the ab sorbed part of the continuum by these ions. The Ce 3+ , Tb 3+ , and Dy 3+ ions quench the OH* emission at 310 nm with a qualitative correlation between the degree of quenching and the standard redox potentials of the pairs Ln IV /Ln III .The characteristic luminescence of the Ln 3+ ions ob served in the sonolysis of air saturated solutions of lan thanide chlorides against the solvent continuum is due to two mechanisms. 1 For CeCl 3 , whose photoluminescence (PL) quantum yield in water is ~1, 2 the appearance of the Ce 3+ band in the spectrum of multibubble sonolumines cence (MBSL) is caused by sonophotoluminescence (SPL), viz., the re emission of the absorbed part of the continuum by cerium aqua ions in the bulk of the solution from the gas phase of cavitation bubbles generated upon acoustic radiation. For TbCl 3 and DyCl 3 , whose PL yields are lower than that of CeCl 3 , the absorption of the solvent luminescence is less considerable and the contribution of SPL to the MBSL intensity is insignificant. The appear ance of the lines from Tb 3+ and Dy 3+ , like the continuum, is caused by the electronic excitation of the sonolumines cence emitters inside the bubbles. Lanthanide can incor porate into the bubbles only in concentrated solutions and, hence, the MBSL of terbium is noticeable beginning from the concentration of 0.05 mol L -1 , whereas the SPL of cerium is observed at the concentration 10 -3 mol L -1 . 1 The detailed mechanism of the intrabubble excitation of the Ln 3+ ions has not earlier 1 been discussed.In the present work, we studied the effect of argon on the MBSL of solutions of CeCl 3 , TbCl 3 , and DyCl 3 to reveal possible routes of its influence on the intensity of the characteristic luminescence of Ln 3+ excited through dif ferent mechanisms. ExperimentalBidistilled water and the salts LnCl 3 •6Н 2 О (reagent grade) were used. The procedure of recording the MBSL spectra for air saturated solutions has been described previously. 1 The solutions were saturated with argon by passing it for 45 min, then the spectra were recorded for 2 min. It was found in special experi ments that the MBSL intensity changed negligibly due to degas sing of the solution (10 mL) during this time, when applying sonication with a frequency of 20 kHz and power of 30 W. The spectra obtained with a resolution of 20 nm are given with out corrections to the spectral sensitivity of the detecting system, viz., the monochromator of an Aminco-Bowman J4 8202 spec trofluorimeter and a Hamamatsu 1P28 photomultiplier. When comparing intensities in different spectral regions, cor...

The influence of the temperature of a liquid on multibubble sonoluminescence of Tb3+ ions in an aqueous solution

“…3), and E a is still larger for the MBSL of water (14.7 kJ/mol). These results substantiate the conclusion [9][10][11][12] that the MBSL of terbium cannot be sonoluminescence but is related to lanthanide ion excitation directly in cavitation bubbles. Indeed, if the mechanism of SPL is correct, we must expect the activation energy for the intensity of MBSL higher than E a for the MBSL of water by the E a value for the PL 1 dependence.…”

“…Note that a factor decreasing E a of MBSL quenching may be a probable increase in the amount of Tb 3+ ions transferred from solution into bubbles as the temperature of the solution increases because of more intense vaporization. To summarize, the results obtained substantiate the conclusions drawn in [9][10][11][12][13][14] concerning the mecha nism of MBSL of lanthanide ions. The observed decrease in the intensity of MBSL of terbium as the temperature of solutions grows is a complex effect caused by the summation of two main acting factors: a decrease in the yield and luminescence of excited Tb 3+ ions in bubbles and temperature quenching of part of excited ions transferred from bubbles into solution volume.…”

“…Indeed, such reemission completely explains glow of Ce 3+ , whose luminescence was caused by d-f transitions [9,12]. However, glow in the sonolysis of ions emitting light in intrashell f-f transi tions (Eu 3+ , Tb 3+ , Gd 3+ , and Dy 3+ ) cannot be explained by SPL [9][10][11][12]. In addition, intrabubble excitation of these ions was also substantiated by the isotope effect (an increase in the intensity of lan thanide luminescence caused by solvent deuteration), which was observed for MBSL in solutions of TbCl 3 [13,14].…”

“…This hypothesis is difficult to prove because of a possible contribution of sonophoto luminescence (SPL) to glow; that is, reemission by Ln 3+ ions in solution volume of partly absorbed radia tion of electronically excited sonolysis products emit ted from bubbles. Indeed, such reemission completely explains glow of Ce 3+ , whose luminescence was caused by d-f transitions [9,12]. However, glow in the sonolysis of ions emitting light in intrashell f-f transi tions (Eu 3+ , Tb 3+ , Gd 3+ , and Dy 3+ ) cannot be explained by SPL [9][10][11][12].…”

“…Tb 3+ ions should therefore be less "sensitive" (with respect to the possibility of excitation) to a decrease in the maximum temperature in bubbles, accordingly, to liq uid temperature than OH radicals. Indeed, experi ments showed that solution saturation with argon, which, like a decrease in liquid temperature, increases the degree of gas compression in bubbles, more weakly influences the intensity of MBSL of terbium com pared with its influence on the intensity of MBSL of water [12]. Note that a factor decreasing E a of MBSL quenching may be a probable increase in the amount of Tb 3+ ions transferred from solution into bubbles as the temperature of the solution increases because of more intense vaporization.…”