Sonoluminescence of aqueous solution of gadolinium chloride

Article abstract of DOI:10.1007/s11172-005-0414-1

A line of the Gd^III ion was detected at 311 nm in the multibubble sonoluminescence spectrum of a concentrated (1 mol L^-1) solution of gadolinium chloride. A comparison with the earlier studied sonoluminescence of the Ce^III and Tb^III ions shows that the Gd^III ion is excited in the volume and/or on the surface of cavitation bubbles upon collisions with hot particles. The efficiency of excitation of the lanthanide ions via this mechanism depends on the type of electron transition. For the same energy of the excited state, the efficiency of Gd^III excitation (f-f transition) exceeds by at least 50 times that of Ce^III excitation (f-d transition).

Full text of DOI:10.1007/s11172-005-0414-1

Russian Chemical Bulletin, International Edition, Vol. 54, No. 6, pp. 1383—1386, June, 2005
1383
Sonoluminescence of aqueous solution of gadolinium chloride
G. L. Sharipov,ꢀ R. Kh. Gainetdinov, and A. M. Abdrakhmanov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
1
41 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347 2) 31 2750. Eꢀmail: ink@anrb.ru
III
A line of the Gd ion was detected at 311 nm in the multibubble sonoluminescence
spectrum of a concentrated (1 mol L– ) solution of gadolinium chloride. A comparison with
1
III
III
III
the earlier studied sonoluminescence of the Ce and Tb ions shows that the Gd ion is
excited in the volume and/or on the surface of cavitation bubbles upon collisions with "hot"
particles. The efficiency of excitation of the lanthanide ions via this mechanism depends on the
III
type of electron transition. For the same energy of the excited state, the efficiency of Gd
excitation (f—f transition) exceeds by at least 50 times that of Ce excitation (f—d transition).
III
Key words: sonoluminescence, lanthanides, photoluminescence, gadolinium chloride.
1
1
Sonolysis and sonoluminescence (SL) are being studꢀ
ied for a long time. However, mechanisms of many proꢀ
cesses accompanying the appearance of cavitation gasꢀ
vapor bubbles in the liquid upon ultrasonication remain
We have earlier studied the SL of concentrated aqueꢀ
ous solutions of lanthanide chlorides (C = 1 mol L– ).
The SL spectra consist of a broad (λ = 250—650 nm)
continuum glow of excited water molecules and OH•
radicals, and the characteristic luminescence bands
1
1
unclear. The characteristic emission lines of dissolved
2
—8
III
III
III
III
metal compounds have previously
been found in the
of Ln , e.g., Tb , Dy , or Ce , are superimposed on
this glow. For the ions with a high photoluminescence
quantum yield in solution (ϕ ≈ 1), the efficiency of charꢀ
SL spectra, indicating their excitation upon sonolysis of
the aqueous solutions. However, this phenomenon is deꢀ
scribed in general features only.
III
acteristic SL is found to be low: no SL of the Pr ion,
which does not absorb in the region of UV emission of the
sonolysis products of water, was found. The lowꢀintensity
It is believed that at low concentrations (10–4—10–3
mol L–1) additives are excited due to chemiluminescence
reactions involving sonolysis products in bubbles of water
molecules that get into the solution volume. At high conꢀ
2
III
SL of the Ce ion is mainly caused by the absorption of
the light emitted from bubbles by the sonolysis products
of water, viz., cerium ions, in the liquid bulk (optical
mechanism) (Fig. 1, insert). The sonoluminescence of
the Tb and Dy ions with lower quantum yields (ϕ ≤ 0.1)
is much more intense than the SL of the cerium ion and is
not related to the optical mechanism. As in Ref. 8, the SL
of these ions was attributed to their electron excitation in
the cavity and/or on the surface of bubbles. This process
is assumed to be much more efficient than the innerꢀ
bubble electron excitation of the Pr and Ce ions,
which do not differ substantially from the Tb and DyIII
ions by the ability of incorporation into the bubbles.
The different efficiencies of SL generation in cavitaꢀ
tion bubbles can be a consequence, first, of differences in
the energy of the excited state of Ln ions (in the case of
praseodymium and cerium, it is ∼ 47 000 and ∼ 32 200 cm–
respectively; for terbium and dysprosium, it is much lower:
∼ 20 000 cm ). Second, the electron states are different:
excitation in praseodymium and cerium is caused by the
f—d transitions, while the f—f transitions produce the
electron states in terbium and dysprosium. Since the
excitation cross sections of lanthanide ions for collisions
of particles were not calculated, experimental data on the
–
1
centrations (>0.1 mol L ), the additives get into gas
bubbles and are excited similarly to water molecules, i.e.,
due to inelastic collisions with other particles in the gasꢀ
III
III
3
8
eous phase heated to high temperature ((3—5)•10 K).
Neither the role of a traditional optical mechanism,
viz., reꢀemission by additives after absorption (mainly in
the UV region) of the luminescence of water molecules,
nor the role of factors affecting the efficiency of innerꢀ
bubble excitation and luminescence of the additives are
considered in the aboveꢀmentioned works.2 Although
states with any quantum numbers can be excited upon
III
III
—8
III
9
collisions of electrons, ions, atoms, and molecules, unꢀ
like optical transitions, the efficiency (cross section) of
excitation depends on both the energy (including the enꢀ
ergy of the formed excited state) and quantum states of
these particles. Both the intrinsic (determined by intramoꢀ
lecular processes) quantum yield of luminescence and
different reactions of quenching by the sonolysis products
should affect the SL intensity of the additives.
III
1
,
–
1
1
0
Lanthanide compounds with characteristic wideꢀrange
absorption and emission spectra, from the UV to IR reꢀ
gion, are best suited to solve these problems.1
0
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1341—1344, June, 2005.
066ꢀ5285/05/5406ꢀ1383 © 2005 Springer Science+Business Media, Inc.
1

1384
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Sharipov et al.
I (rel. units)
spectra recording) solutions was maintained at a level of 4±2 °C.
One spectrum was recorded within ∼ 1 min.
S2
I (rel. units)
2
III
The SL yield of the Gd ions was estimated by a compariꢀ
4
3
2
1
0
0
0
0
son of integrated glows of the band at λ = 311 nm and a referꢀ
1
1
20
00
4
ence radioluminescent light source (λ
= 520 nm) similarly to
max
1
3
a known procedure. The total number of photons emitted by
gadolinium from the whole cavitation region was estimated with
allowance for the spectral sensitivity of the PMT and geometry
of measurement.
S1
5
8
6
4
2
0
0
0
0
1
3
00
500 λ/nm
Results and Discussion
2
The SL spectra of bidistilled water and aqueous soluꢀ
tions of GdCl and CeCl are given in Fig. 1. It is seen
4
3
3
3
that the spectrum of a solution of gadolinium chloride
contains an intense band with a maximum at λ = 311 nm
6
8
corresponding to the transition P7/2 → S
in the
7/2
3
00
400
500
600
λ/nm
III
10
Gd ion. The line corresponding to the transition
6
8
P5/2 → S
(λ = 306 nm) is not resolved under the
Fig. 1. Sonoluminescence spectra (T = 4±2 °C) of aqueous
7/2
1
1
experimental conditions. The intensity of the characterisꢀ
tic band of the gadolinium ion, as in the case of the SL of
solutions of gadolinium chloride (1), cerium chloride (2) (C =
–
1
1
mol L ), and bidistilled water (3) and the reduced spectrum
1
1
of the continuum glow of water during sonolysis of a cerium
solution (4). The spectrum (5) obtained by subtraction of curve
the terbium ion, increases linearly with an increase in
–
1
the concentration from 0.05 mol L (detection limit) to
4
from curve 2 in a region of 320—450 nm and coinciding with
–1
1
mol L . In addition, high concentrations of the gadoꢀ
III
the photoluminescence spectrum of Ce is shown in insert. The
hatched regions S and S equal in surface area are the part of
11
linium ion, as well as other lanthanide ions or alkaline
metal salts,
1
2
4—8
noticeably increase the intensity of the
the bubble glow of water absorbed by cerium and the sonoꢀ
luminescence emitted by cerium, respectively.
continuum glow of water (up to a factor of four near the
maximum at λ = 420 nm). These regularities, as well as
IV
III
the high redox potential of the Gd /Gd pair (E° =
7
influence of these factors on the innerꢀbubble SL of lanꢀ
thanides are required.
.9 V), make it possible to exclude the earlier proposed2
1
4
redox chemiluminescence mechanism for the SL of aqueꢀ
ous solutions of the organic terbium chelate (oxidation of
For this purpose, in this work we studied the earlier
unknown SL of an aqueous solution of gadolinium chloꢀ
•
the emitter or its precursor with the OH radical followed
III
ride. The energy of the excited state of the Gd ion
by excitation accompanying reduction with a hydroꢀ
gen atom).
(
∼ 32 000 cm–1) is higher than the resonance levels of the
terbium and dysprosium ions and is close to the level of
the excited state of the cerium ion. At the same time, the
excitation of the gadolinium, terbium, and dysprosium
ions is caused by a transition of the f—f type.
It is known10 that the absorption spectrum of the GdIII
aqua ion contains bands at 272, 273, and 275 nm (i.e., at
the UV spectral edge of the SL continuum of water)
with molar absorption coefficients of 3.16, 1.12, and
–
1
–1
1
.9 L mol cm , respectively. A small linewidth and
Experimental
low molar absorption coefficients impede the optical exꢀ
citation of the gadolinium aqua ion during sonolysis. When
Gadolinium chloride was prepared from metallic gadolinium
of 99.9% purity and hydrochloric acid (special purity grade)
III
assuming that the SL of the Gd ion appears via the
1
2
optical mechanism, then, taking into account its photoꢀ
using a known procedure. The experimental setup is similar to
1
5
that described earlier.11 Sonoluminescence spectra were recorded
luminescence quantum yield in solution (ϕ ≈ 0.2), it is
difficult to explain a higher glow intensity at λ = 311 nm
on an AMINCOꢀBOWMAN spectrofluorimetric technique with
a HAMAMATSU 1P28 photomultiplier tube (PMT). To obtain
acoustic oscillations, an ACE GLASS ultrasonic generator with
a titanium waveguide (length 130 mm, diameter 6 mm, and
working frequency 20 kHz) equipped with a sensor of the emitꢀ
ted acoustic power was used. Experiments were carried out at a
radiation power of ∼ 30 W. Sonoirradiation was carried out in a
steel thermostatted 20ꢀmL reactor with a quartz window. Glow
III
compared to the SL intensity of the Ce ion (ϕ ≈ 1) (see
Fig. 1). The contributions from the gadolinium and terꢀ
11
bium glows (ϕ ≈ 0.1) to the SL of an aqueous solution
are close. Therefore, the gadolinium glow in the solution
bulk related to the absorption of radiation from water and
•
OH radicals is not the main source of its SL. Sonoꢀ
3
excitation of gadolinium can be explained by the innerꢀ
was detected from a bubble cluster with a volume of ∼ 1 cm .
1
1
Sonoluminescence spectra were recorded with the spectral resoꢀ
lution ∆λ = 20 nm. The temperature of all airꢀsaturated (before
bubble mechanism proposed previously for the SL of
terbium and dysprosium (see below).

Sonoluminescence of gadolinium chloride
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
1385
8
differences in energies of the excited state of the LnIII ions
on their innerꢀbubble SL is less significant than the effect
of the electron transition type.
According to the modern concepts, "hot" particles
are formed inside a pulsatory cavitation bubble due to its
compression in a ultrasonic field. Collisions of the "hot"
particles produce electronꢀexcited water molecules and
OH radicals. It is assumed that both the contents of a
bubble and an adjacent liquid layer with a thickness up to
Note that the SL efficiencies of the GdIII and CeIII
ions were compared ignoring the influence of possible
quenching reactions of luminescent states of these ions by
the sonolysis products. The question arises: which step of
innerꢀbubble processes is more affected by the excited
•
8
–
5
1
0
cm can be heated at maximum compression. The
parameters achieved at the liquid—gas interface are suffiꢀ
cient for the evaporation of nondissociated metal salts, in
particular, lanthanides. Getting into the gas phase, the
III
state nature, namely, the primary step of Ln ion excitaꢀ
tion upon collisions or subsequent steps of radiation and
radiationless deactivation of the excited ions?
III
Ln ions can be excited upon inelastic collisions with
"
hot" particles and, perhaps, due to the electronꢀexcitaꢀ
At the first sight, the low SL intensity of the cerium
1
1
tion energy transfer if the collisions occur with the already
excited particles, for example, H O* and OH*.
The estimates presented below show that the ions at
the liquid—gas interface, for instance, in a thin "monoꢀ
aquaionic" layer, can also be excited upon collisions.
To check this hypothesis, we estimated the luminesꢀ
cence yield of the Gd ions. We found that for a solution
with C = 1 mol L at a radiation power of ∼ 6.4•10
the photoacoustic efficiency is ∼ 2.1•10
ber of excited ions generated per period of an ultrasonic
ion and no SL of the praseodymium ion can also be
attributed to the innerꢀbubble quenching reactions. Ions
with the f—d type of excitation are good electron doꢀ
2
1
9,20
•
nors
and can react, e.g., with the OH radical.
Се3+* + OH•
Се4+ + OH–
III
Pr3+* + OH•
Pr4+ + OH–
–
1
–10
W
–
11
and the numꢀ
However, the probability of this quenching is low unꢀ
•
der the experimental conditions, because the OH radiꢀ
5
21
field oscillation is N * ≈ 10 .
cals are efficiently trapped by the known acceptor, viz.,
e
Let us estimate the efficiency of GdIII* ion generation
upon collisions, ignoring a possibility of excitation in the
bubble volume and assuming that the latter occurs only
on the bubble surface. For this purpose, by analogy to
Ref. 8, we estimate the minimum number of gadolinium
ions on the cavitation bubble surface at the moment of its
maximum compression, when a glow flash occurs. Since
Cl ions. They are present in the solution and, hence, in
–
the bubbles in a much higher concentration than that of
the excited lanthanide ions having, in addition, a short
1
0
lifetime (44 ns for cerium).
2
2
Sonolysis is known to have many common features
with radiolysis. Therefore, note that the efficiencies of SL
2
3
generation for lanthanides and the earlier determined
relative yields of their luminescence during radiolysis corꢀ
relate. It should be emphasized that, similarly to innerꢀ
bubble collisions with "hot" particles, the main source of
lanthanide ion excitation during radiolysis of aqueous soꢀ
lutions is the direct effect of radiation, i.e., their collisions
with ionizing particles. The study of the effect of radical
acceptors on radioluminescence of lanthanide ions showed
a certain influence of track quenching reactions on the
luminescence yield. However, the latter is more signifiꢀ
–
4
16,17
the minimum radius of a bubble is ∼ 10 cm
kinetic diameter of water molecules is 4•10 cm, the
total number of molecules on the bubble surface is ≥10 .
Since the molar fraction of dissolved gadolinium is equal
to 1 : 55 (55 is the number of water moles in solution),
the number of the gadolinium ions on the bubble surꢀ
face is ∼ 2•10 . For the bubble concentration n ≈
1
the bubble surface is N ≈ 2•10 —2•10 and the fraction
of the excited ions N */N is ∼ 10–5. Thus, only an insigꢀ
nificant portion of the Gd ions capable of excitation on
the surface is excited, which is quite reasonable in the
framework of the collision mechanism.
and the
–
8
8
6
3
4
–3 18
0 —10 cm
,
the total number of gadolinium ions on
9
10
III
cant for the Tb ion with the f—f type of excitation
e
III
23,24
(quenching with a hydrated electron)
rather than for
•
the cerium ion (quenching with the OH radical).*
III
Tb3+* + е–aq
Tb2+ (or Tb3+ + е–aq*)
These data suggest that the Gd ions are excited upon
collisions, most likely, due to the transformation of the
kinetic energy of "hot" particles into the electronꢀexcitaꢀ
tion energy rather than the energy transfer from the exꢀ
* The excited state of the terbium ion has a much longer lifetime
1
0
3+
(400 µs for the aqua ion ) than the Ce * ion and, probably, it
is more vulnerable for quenching by the radiolysis products or
water sonolysis. Note that the lifetime of the Tb3 * ion is comꢀ
parable with the oscillation period of a bubble, which can disapꢀ
pear after one or several oscillations due to collapse, yielding the
excited and radical products to the solution. The transfer of the
cited particles H O* and OH*. Otherwise, the continuum
2
+
glow of water in the shortꢀwave region would be quenched.
We can conclude the following. Although the energy
gap between the ground and first electronꢀexcited states is
III
considerable and close to that for the Ce ion (f—d type),
3+
Tb * ions from the gaseous to aqueous phase provides addiꢀ
III
the Gd ion (f—f type) is excited in bubbles with an
tional (compared to the cerium ion) opportunities for quenchꢀ
ing during sonolysis. Nevertheless, the SL intensity of the terꢀ
bium ion is higher than that of the cerium ion.
efficiency close to that of the innerꢀbubble excitation of
III
III
the Tb and Dy ions (f—f type). Thus, the influence of

1
386
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 6, June, 2005
Sharipov et al.
However, the aboveꢀpresented quenching reaction
have no decisive influence on the radioluminescence yield,
which would strongly change the ratio between the lumiꢀ
nescence yields of different ions.23 Most likely, this conꢀ
clusion is also true for innerꢀbubble SL, the more so,
sonolysis is characterized by the formation of a weaker
6. C. Sehgal, R. G. Sutherland, and R. E. Verral, J. Phys.
Chem., 1980, 84, 529.
7
8
9
. C. Sehgal, R. P. Steer, R. G. Sutherland, and R. E. Verral,
J. Chem. Phys., 1979, 70, 2242.
. M. A. Margulis and A. F. Dmitrieva, Zh. Fiz. Khim., 1982,
5
6, 875 [Russ. J. Phys. Chem., 1982, 56 (Engl. Transl.)].
. G. F. Drukarev, Stolknoveniya elektronov s atomami i
molekulami [Collisions of Electrons with Atoms and Molecules],
Nauka, Moscow, 1978, 256 pp. (in Russian).
(
(
compared to a hydrated electron) reducing agent
H atom) and a more diffuse distribution of the primary
OH and H• radicals. For sonolysis and radiolysis of
aqueous solutions, the terbium, dysprosium, and gadoꢀ
linium ions luminesce and are excited, evidently, much
more efficiently than the cerium and praseodymium ions.
Thus, the influence of the excitation state type on the
efficiency of innerꢀbubble excitation of lanthanide ions
rather than on the step of their quenching seems most
probable for explanation of the results obtained.
•
22
10. N. S. Poluektov, L. I. Kononenko, N. P. Efryushina, and
S. V. Bel´tyukova, Spektrofotometricheskie i lyuminestsentnye
metody opredeleniya lantanoidov [Spectrophotometric and Luꢀ
minescence Methods for Determination of Lanthanides],
Naukova Dumka, Kiev, 1989, 256 pp. (in Russian).
1
1. G. L. Sharipov, R. Kh. Gainetdinov, and A. M.
Abdrakhmanov, Izv. Akad. Nauk, Ser. Khim., 2003, 1866
[
Russ. Chem. Bull., Int. Ed., 2003, 52, 1969 (Engl. Transl.)].
1
2. Yu. V. Karyakin and I. I. Angelov, Chistye khimicheskie
reaktivy [Pure Chemical Reagents], Khimiya, Moscow, 1974,
408 pp. (in Russian).
13. L. V. Levshin and A. M. Saletskii, Lyuminestsentsiya i ee
izmerenie [Luminescence and Its Measurements], Izdꢀvo Mosk.
Gos. Univ., Moscow, 1989, 279 pp. (in Russian).
4. A. K. Pikaev, V. P. Shilov, and V. I Spitsyn, Radioliz vodnykh
rastvorov lantanidov i aktinidov [Radiolysis of Aqueous Soluꢀ
tions of Lanthanides and Actinides], Nauka, Moscow, 1983,
This effect can quantitatively be estimated in the first
approximation, i.e., ignoring the spectral sensitivity of the
PMT in the absorption and emission regions of cerium
and gadolinium ions, losses for multiple reemission (in
the case of cerium), and influence of possible reactions of
innerꢀbubble quenching and changing ϕ of the gadolinium
ions that transfer to the gaseous phase. A comparison of
the integrated intensities of the radiation absorbed by ceꢀ
1
4
3 (in Russian).
rium from bubbles (S = 505±25 rel. units) and the glow
1
15. Y. Haas, G. Stein, and E. Würzberg, J. Chem. Phys., 1973,
58, 2777.
emitted by cerium (S = 507±25 rel. units) shows (see
2
Fig. 1, insert) that the SL intensity of the cerium ion,
which could be related to its innerꢀbubble excitation, viz.,
I = S – S ϕ, is lower than the detection threshold and
16. M. A. Margulis and A. F. Dmitrieva, Zh. Fiz. Khim., 1982,
56, 323 [Russ. J. Phys. Chem., 1982, 56 (Engl. Transl.)].
1
7. M. A. Margulis, Akust. Zh. [Acoustic J.], 1975, 21, 760 [in
2
1
Russian].
does not exceed 0.1S = 50 rel. units, taking into account
1
1
8. M. A. Margulis, Zvukokhimicheskie reaktsii
i sonoꢀ
measurement errors S and S (5%). A comparison of this
1
2
lyuminestsentsiya [Sonochemical Reactions and Sonolumineꢀ
scence], Khimiya, Moscow, 1986, 288 pp. (in Russian).
9. G. J. Kavarnos and N. J. Turro, Chem. Rev., 1986, 86, 401.
0. G. L. Sharipov, S. S. Ostakhov, N. Sh. Ableeva, A. I.
Voloshin, V. P. Kazakov, and G. A. Tolstikov, Izv. Akad.
Nauk, Ser. Khim., 1993, 1824 [Russ. Chem. Bull., 1993, 42,
value with the integrated SL intensity of the gadolinium
ion (surface area of the band at λ = 311 nm, which is
equal to 2840±140 rel. units) suggests that at the same
excitation state energy the efficiency of excitation of an
ion of the f—f type in innerꢀbubble processes is more than
1
2
1
748 (Engl. Transl.)].
5
0ꢀfold higher than that of excitation of an ion of the
2
2
1. A. K. Pikaev, Sovremennaya radiatsionnaya khimiya. Radioliz
gazov i zhidkostei [Modern Radiation Chemistry. Radiolysis of
Gases and Liquids], Nauka, Moscow, 1986, 440 pp. (in
Russian).
2. M. A. Margulis, Osnovy zvukokhimii (khimicheskie reaktsii v
akusticheskikh polyakh) [Foundations of Sonochemistry
f—d type.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 05ꢀ03ꢀ
7904).
9
(
Chemical Reactions in Acoustic Fields], Vysshaya Shkola,
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2
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. S. Kulmala, T. AlaꢀKleme, M. Latva, K. Haapakka, and
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3
4
5
. C. Sehgal, R. G. Sutherland, and R. E. Verral, J. Phys.
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Received April 27, 2004;
in revised form September 14, 2004