Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar

Transitions from ionic states A²⁺X– of alkalihalides CsF, CsCl and RbF isolated in solid Ne and Ar films recorded under pulsed e-beam excitation are studied. The B(²∑₁/₂)-X(²∑₁/₂) and C(²П₃/₂)-A(²П₃/₂) luminescence bands of Cs2+F– (196.5 nm, 227 nm), Cs²⁺Cl– (220.1 nm, 249.2 nm) and Rb²⁺F– (136 nm)...

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Hauptverfasser: Śliwiński, G., Frankowski, M., Schwentner, N.
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spelling nasplib_isofts_kiev_ua-123456789-1289382025-02-09T22:44:44Z Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar Śliwiński, G. Frankowski, M. Schwentner, N. Spectroscopy in Cryocrystals and Matrices Transitions from ionic states A²⁺X– of alkalihalides CsF, CsCl and RbF isolated in solid Ne and Ar films recorded under pulsed e-beam excitation are studied. The B(²∑₁/₂)-X(²∑₁/₂) and C(²П₃/₂)-A(²П₃/₂) luminescence bands of Cs2+F– (196.5 nm, 227 nm), Cs²⁺Cl– (220.1 nm, 249.2 nm) and Rb²⁺F– (136 nm) in Ne, and a weakerB–X emission of Cs²⁺F– (211.2 nm) in Ar are identified. For CsF the depopulation of the A²⁺X– state is dominated by the radiative decay. A ratio of the recorded exciplex emission intensities of I(CsF)/I(CsCl)/I(RbF) = 20/5/1 reflects the luminescence efficiency and for RbF and CsCl a competitive emission channel due to predissociation in the A²⁺X⁻(B²∑₁/₂) state is observed. For these molecules an efficient formation of the state X*₂ is confirmed through recording the molecular D`(³П₂g)-A`(³П₂u) transition. A strong dependence of the luminescence intensities on the alkalihalide content reveals quenching at concentrations higher than 0.7%. 2003 Article Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar / G. Śliwiński, M. Frankowski, N. Schwentner // Физика низких температур. — 2003. — Т. 29, № 9-10. — С. 1113-1117. — Бібліогр.: 18 назв. — англ. 0132-6414 PACS: 78.45.+h, 78.55.Fv https://nasplib.isofts.kiev.ua/handle/123456789/128938 en Физика низких температур application/pdf Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
topic Spectroscopy in Cryocrystals and Matrices
Spectroscopy in Cryocrystals and Matrices
spellingShingle Spectroscopy in Cryocrystals and Matrices
Spectroscopy in Cryocrystals and Matrices
Śliwiński, G.
Frankowski, M.
Schwentner, N.
Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
Физика низких температур
description Transitions from ionic states A²⁺X– of alkalihalides CsF, CsCl and RbF isolated in solid Ne and Ar films recorded under pulsed e-beam excitation are studied. The B(²∑₁/₂)-X(²∑₁/₂) and C(²П₃/₂)-A(²П₃/₂) luminescence bands of Cs2+F– (196.5 nm, 227 nm), Cs²⁺Cl– (220.1 nm, 249.2 nm) and Rb²⁺F– (136 nm) in Ne, and a weakerB–X emission of Cs²⁺F– (211.2 nm) in Ar are identified. For CsF the depopulation of the A²⁺X– state is dominated by the radiative decay. A ratio of the recorded exciplex emission intensities of I(CsF)/I(CsCl)/I(RbF) = 20/5/1 reflects the luminescence efficiency and for RbF and CsCl a competitive emission channel due to predissociation in the A²⁺X⁻(B²∑₁/₂) state is observed. For these molecules an efficient formation of the state X*₂ is confirmed through recording the molecular D`(³П₂g)-A`(³П₂u) transition. A strong dependence of the luminescence intensities on the alkalihalide content reveals quenching at concentrations higher than 0.7%.
format Article
author Śliwiński, G.
Frankowski, M.
Schwentner, N.
author_facet Śliwiński, G.
Frankowski, M.
Schwentner, N.
author_sort Śliwiński, G.
title Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
title_short Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
title_full Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
title_fullStr Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
title_full_unstemmed Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar
title_sort luminescence and formation of alkalihalide ionic excimers in solid ne and ar
publisher Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
publishDate 2003
topic_facet Spectroscopy in Cryocrystals and Matrices
url https://nasplib.isofts.kiev.ua/handle/123456789/128938
citation_txt Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar / G. Śliwiński, M. Frankowski, N. Schwentner // Физика низких температур. — 2003. — Т. 29, № 9-10. — С. 1113-1117. — Бібліогр.: 18 назв. — англ.
series Физика низких температур
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AT frankowskim luminescenceandformationofalkalihalideionicexcimersinsolidneandar
AT schwentnern luminescenceandformationofalkalihalideionicexcimersinsolidneandar
first_indexed 2025-12-01T11:59:27Z
last_indexed 2025-12-01T11:59:27Z
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fulltext Fizika Nizkikh Temperatur, 2003, v. 29, Nos. 9/10, p. 1113–1117 Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar G. Œliwiñski and M. Frankowski Polish Academy of Sciences, IF-FM, Fiszera 14, PL 80-952 Gdansk, Poland E-mail: gerards@imp.gda.pl N. Schwentner Institute of Experimental Physics, Free University, Arnimallee 14, Berlin D-14195, Germany Transitions from ionic states A2+X– of alkalihalides CsF, CsCl and RbF isolated in solid Ne and Ar films recorded under pulsed e-beam excitation are studied. The B /( )2 1 2� –X /( )2 1 2� and C /( )2 3 2� –A /( )2 3 2� luminescence bands of Cs2+F– (196.5 nm, 227 nm), Cs2+Cl– (220.1 nm, 249.2 nm) and Rb2+F– (136 nm) in Ne, and a weaker B–X emission of Cs2+F– (211.2 nm) in Ar are iden- tified. For CsF the depopulation of the A2+X– state is dominated by the radiative decay. A ratio of the recorded exciplex emission intensities of I(CsF)/I(CsCl)/I(RbF) = 20/5/1 reflects the lu- minescence efficiency and for RbF and CsCl a competitive emission channel due to predissociation in the A X2 2 1 2 � �( )B /� state is observed. For these molecules an efficient formation of the state X2 � is confirmed through recording the molecular � � �D Ag u( ) ( )3 2 3 2� � transition. A strong dependence of the luminescence intensities on the alkalihalide content reveals quenching at concentrations higher than 0.7%. PACS: 78.45.+h, 78.55.Fv 1. Introduction Luminescence of ionic excimers covers the VUV and deep UV wavelength region and represents an in- teresting perspective for an extension of the gas phase excimer media towards shorter wavelengths. Since the first considerations around 1985 [1,2] the ionic sys- tems are extensively investigated. Spectroscopic stud- ies in the gas phase provided emission from ionic states A2+X– of alkalihalides (AX), and from diatomic (RgA)+ and triatomic (Rg2A)+ rare gas alkali ions [3–8]. Optical gain has been achieved [9], however, the recent kinetic studies indicate quenching processes which can seriously limit amplification [10]. The electronic configurations for the family of alkalihalide ions (AX)+ correspond to those of rare gas halides RgX in the ground state and correlate to the atomic states A+(1S) and X(2P). Also the ionically bound upper states (A2+X–) due to transfer of an alkali 5p-core electron to the halogen are isoelectronic to Rg+X– exciplex states with similar po- tential surfaces and correlate to A2+(2P) and X–(1S) atomic states. Since the potential of the lower (AX)+ state has a dissociative character it is anticipated, that population inversion can be obtained in these systems. The upper bound state can be directly populated by photoionization of AX. Radiative transitions with large cross-section for stimulated emission and short radiative lifetimes of the order of 1 ns can be expected for A2+X–. These ions considered in the condensed phase combine the favorable properties of the short wavelength, strong excimer emissions known from the gas phase with the high number densities of excited states attainable in the solid. Recently deep UV fluorescence bands of A2+X– ions were observed for CsF, CsCl and RbF isolated in Ne and Ar matrices under e-beam excitation [11,12]. It was shown, that the exciplex states B / 2 1 2� and X / 2 3 2� are effectively populated via host excitons resulting mainly in the B X/ / 2 1 2 2 1 2� �� emission. Also a much weaker C A/ / 2 3 2 2 3 2� �� transition for the ionic states of CsF and CsCl was observed. The observed transitions were red shifted compared to the gas phase due to interaction with the dielectric host. The first indication for the homonuclear � � �D A transi- tion of Cl2 � and F2 � was reported and ascribed to predissociation via the A+X� state [13]. © G. Œliwiñski, M. Frankowski, and N. Schwentner, 2003 1114 Fizika Nizkikh Temperatur, 2003, v. 29, Nos. 9/10 In this work the spectroscopic data and formation of the ionic states A2+X– of alkalihalides: CsF, CsCl and RbF isolated in thin Ne and Ar films, are studied. Conclusions on the formation efficiency of X2 � mole- cules due to predissociation in the A2+X–(B / 2 1 2� ) state of RbF and CsCl following from the concentra- tion dependent measurements are discussed. 2. Transitions from alkalihalide ionic states For understanding of the excitation and decay pro- cesses it is instructive to consider the energy level scheme of the alkalihalide states involved in the ob- served radiative transitions. Since the problem was dis- cussed for the CsCl elsewhere [12] here just features will be recalled which are valid for the general case of the A+X– ionic states. For this purpose it is convenient to consider the energy of states in units equal to the binding potential of the AX ground state and the internuclear separation in units of equilibrium distance re – see Fig. 1. The states relevant for discussion are de- scribed by potential curves and for the other ones only positions of the dissociation limits are given. The rare gas excitons formed in the host by the pulsed electron beam are responsible for the A+(1S) core ionization of the 1� ground state of AX molecules (an upward arrow in Fig. 1). Due to the equilibrium distance re in this state the higher vibrational levels ��� of the A2+(2P)X–(1S) state are populated, and a fast radia- tionless relaxation to the ��� = 0 level occurs because of the low temperature around 5 K. It is followed by the bound-free radiative transition A X AX2� � � �( ) h� (1) to the repulsive part of the lower X / 2 1 2� potential and characterized by the emission of UV photons on a time scale close to one nanosecond (a downward ar- row, Fig. 1). Energy wise population of the closely spaced B and C states of A2+X– is equally likely and emissions from these states are observed in contrary to the D state which lies higher in energy by the 2 3 2 2 1 2P P/ /� spin-orbit splitting of the A2+ ion. The bound states, i.e. the ground state 1�, the A+X*, and the ionic B / 2 1 2� , potential curves in Fig. 1 are based on the truncated Rittner potential (at 1/r4) with the effect of the dielectric host taken into ac- count by introducing the1/ factor into the coulombic and 1/r4 terms. Bond lengths and polarizabilities are taken from literature [4,14]. For the lower A+X state the Born–Mayer potential V r r re( ) exp[ ( )]� � � �0 0 (2) is used with the assumption that the consideration re- fers to the vicinity of the equilibrium distance re, with 0 being the energy of the lower state at r = re. The shape of V(r) and also the 0 and �0 values are derived from experimental data for the gas phase B–X transitions of A2+X– ions. The potential minima of the X / 2 1 2� states are taken equal to their gas phase counterparts [4]. The transition energies observed in experiment are red shifted by E relative to the gas phase. This can be explained by means of the cavity shell model for a transition dipole moment � given by the relation ( ) ( ) � 2 3� C Ed (3) with C /( ) . ( ) ( ) � � �0125 2 1 1 , d corresponding to the cavity diameter, and being the dielectric constant of the surrounding. The measured E values yield the estimates for � and the measured transition energies result in potential minima of the upper A2+X–(B / 2 1 2� ) states with the red shifts reflecting the solvation energy of the ionic states of AX molecules. For CsCl and RbF it can be deduced from Fig. 1, that the Frank—Condon region corresponding to the G. Šliwiòski and M. Frankowski, N. Schwentner 1 0 1 2 3 4 5 0.7 1.0 1.3 1.7 2.0 � E n e rg y, a rb .u n its ( P)2 A++ X ( S)1+ A+ + +X +XA + A+*+ X A+( S)1 +X ( P)2* A+( S)1 + + X ( S)1 A+( S)1 X ( P)2 VUV/UV Iuminescence B2 �1/2 �1/2X2 �0 1 excitation Internuclear distance, re Fig. 1. The potential energy diagram of the alkalihalides; energy and internuclear separation are in units of the ground state binding potential, and re, respectively; the relevant states are described by the shell configurations and for the other ones only the energetic positions at r � � are given; states C2� and A2� resulting from the spin-orbit splitting of the upper and lower excimer state, respectively, are not shown for simplicity. Selective exci- tation of the ground state A+X– molecule is provided by the e-beam via rare gas excitons — dashed arrow. The ra- diative decay follows a fast radiationless relaxation to the � �� 0 level of the A2+X– ionic bound state. excitation of the 1� state falls close to the crossing point of the A2+X– and A+X� potential surfaces. This indicates predissociation of the A2+X– state as the probable depopulation channel due to the reaction A2+X– A+ + X� (4) which is accompanied by a partial, nonradiative en- ergy loss. Similar to the gas phase results [5] the com- peting predissociation effect is only observed for CsCl and RbF doped samples and in both cases the X2 � mo- lecular emission X X2 2 � � �h h h� � �1 1, (5) occurs. However, in the host a strong cage effect traps the excited X* atoms in the lattice. This leads to a de- crease of the population of X2 molecules finally formed in the ground state. For CsF doped samples the X2 � emission was not observed so in the matrix as well as in the gas phase. The difference in separations of the crossing point of A2+X– and A+X* potentials from the bottom of the 1� potential (re = 1) in Fig. 1, and also the longer radiative lifetime of the C state explain the low intensity of the C–A band for CsF and CsCl in Ne obtained from experiment. The spectroscopic data of the observed ionic transitions for RbF, CsCl, and CsF are calculated following the procedure described previ- ously [15], and are given in Table. Table Spectroscopic properties of matrix isolated, core excited RbF, CsF and CsCl alkalihalides in the VUV and deep UV spectral range: �em — peak position, fwhm — halfwidth, � s — cross section for stimulated emission, and �f — radiative lifetime Molecule, transition Matrix �em, nm fwhm, nm � s, 10–16 cm2 �r, ns Rb++F– B X� Ne 136 4.5 1.5 0.9 Cs++F– B X� Ne 196.5 9.5 2.5 1.2 C A� Ne 227.1 15 0.22 11.3 B X� Ar 211.2 11.3 2.74 0.8 Cs++Cl– B X� Ne 220.1 10.4 2.22 1.4 C A� Ne 249.2 14.8 0.29 12.6 As the most of data obtained refer to the Ne host a comment should be added for the transition energies observed in the solid. These are shown as the ma- trix-dependent (Ne, Ar, or Kr) peak positions of the emission bands together with respective data from gas phase measurements and those of the solid state XeF excimer for reference – Fig. 2. The peak positions are given for optimal contents of the alkalihalides CsF (0.45% in Ar, and 0.7% in Ne), CsCl (0.37%), and RbF (0.6%) in solid Ar and Ne films. The variable ( ) ( ) � �1 2 1/ describes the host interaction and slanted lines connect data of the same dopant. In com- parison to the gas phase results [5] the matrix shift of the B X� luminescence from the ionic states of RbF, CsF and CsCl has a value of 0.43, 0.39 and 0.33 eV, respectively. This is in a good agreement with values of 0.3–0.4 eV predicted from relation (3) and coin- cides with the results obtained for the XeF excimer in solid Ne and Ar [15,16]. Moreover, the values ob- tained so far from experiment (solid data points) al- low to deduce the estimates of transition energies for Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar Fizika Nizkikh Temperatur, 2003, v. 29, Nos. 9/10 1115 Ne Matrix Ar Kr 0 4 5 6 7 8 9 10 Rb F (B X)++ Cs F (B X)++ Cs Cl (B X)++ Cs F (C A)++ Cs Cl (C A)++ +Xe F (D X) 0.1 0.2 ( 1)/(2 + 1) Fig. 2. The matrix-dependent transition energies of the e-beam excited CsF, CsCl, and RbF in Ar and Ne solid films for the optimal alkalihalide concentrations, and XeF data for reference; values for ( ) ( ) � � �1 2 1 0/ correspond to the gas phase data already measured (solid data points) and postulated (hollow points). 1116 Fizika Nizkikh Temperatur, 2003, v. 29, Nos. 9/10 emission bands not observed yet in the solid and in the gas phase as well (hollow data points). 3. The concentration effect The measured intensities of the B–X band are highly sensitive to changes in the original sample composition. Dependences of the peak intensity values versus the dop- ant concentrations in Ne films presented in the form of experimental data sets for CsF, RbF (up and down tri- angles), and CsCl (squares) are summarized in Fig. 3. The dependence observed for CsCl is more pronounced than for CsF and for RbF only two data points are avail- able due to the relatively low signal. In all cases the op- timal alkalihalide content corresponding to the maxi- mum band intensity lies around 0.6–0.8% and is in accordance with the data obtained for the gas phase [4] and also coincides with those from our previous results reported for XeF [15,16]. A comparison of the band in- tensities for the optimal concentrations related to the highest one (CsF) lead to the ratio of I(CsF)/I(CsCl)/I(RbF) = 20/5/1 and reflects the energy transfer efficiency for the investigated species. In the case of CsF a change of the concentration dependent intensity of almost two orders of magnitude is observed. The data for CsCl indicate on weaker concentration de- pendence for samples doped below optimum than for the higher doped ones. In the low doping range exclusively an occurrence of the predissociation of molecules in the ionic state can be observed. This is confirmed by the de- tailed analysis of the CsF and CsCl spectra reported elsewhere [11,12]. The relevant decay channels of the Cs2+Cl–( )B / 2 1 2� state become more evident when the � � �D Ag u( ) ( )3 2 3 2� � transition of the Cl2 � molecule is taken into account. An appearance of the molecular emission can only be observed for CsCl content not ex- ceeding values of about 0.6–0.7%. The intensity of this transition is even much larger from that of B–X for lower concentrations, around 0.1–0.2 %. This together with a decrease of the Cl2 � band intensity for CsCl con- tent increasing in that range reflects a strong competi- tion between the deep UV emission and the concentration quenching process which is due to short-range energy mi- gration, aggregation and also self-absorption by the ground state CsCl( )1� molecules. For a concentration increase in the range from about 0.4 up to 0.9% the optimal values of the dopant content correspond to the highest band in- tensities. The AX content larger than 0.9% results in a decrease of the B–X band intensities. Moreover, in that doping region a rapid growth of the intrinsic fluores- cence bands originating from aggregates occurs. In the case of CsF the concentration quenching seems to repre- sent the main negative contribution to the emission effi- ciency of the excimer band. In general, the effect ob- served most clearly for CsCl is representative for the decay of (AX)+ states of alkalihalides in general. This is supported by the similar concentration dependences of the band intensities observed for CsF and in part for RbF, too [17,18]. 4. Conclusion The favorable population of the A2+X– state of alkalihalides by ionization of the trapped AX mole- cules via host excitons of solid Ne and Ar can be de- duced from the energy level scheme and is confirmed experimentally. The B X/ /( ) ( )2 1 2 2 1 2� �� radiative transition from ionic states represents the most effi- cient depopulation channel for e-beam excited, rare gas matrix-isolated CsF, CsCl and RbF. Also the much weaker emission bands C A( ) ( )2 2� �� of Cs2+F– and Cs2+Cl– occur besides the intrinsic lumi- nescence bands of aggregates. For RbF and CsCl the concentration dependent formation of X2 � molecules due to predissociation in the A2+X–( )B / 2 1 2� state is observed in experiment. The resulting molecular tran- sition �D g( )3 2� – �A u( )3 2� competes efficiently with the exciplex emissions at low doping concentrations around 0.1%. A strong dependence of the emission in- tensities on the alkalihalide content leads to aggrega- G. Šliwiòski and M. Frankowski, N. Schwentner a b CsF CsCl RbF CsCl solid Cl 2* 10 10 4 3 0 0.1 0.1 1 1 Concentration, % In te n si ty (c o u n ts ) 1 2 Fig. 3. Emission intensities of the B X� transition of the A2+X– exciplexes vs. the AX concentration in Ne solid films for CsF (�), CsCl (�) and for RbF (�) (a), and the case of CsCl doped Ne sample; luminescence intensi- ties of the Cl2 � molecular transition � � �D Ag u( ) ( )3 2 3 2� � and of the intrinsic band of CsCl aggregates (245 nm), re- lated to the B X/ / 2 1 2 2 1 2� �� band intensity vs. concen- tration (b); concentrations are percentages and intensities are the peak values measured. tion and quenching at doping concentrations higher than the optimal range of about 0.7 %. Marked differ- ence in the B–X emissions intensities observed for alkalihalides CsF, CsCl and RbF is explained by the position of the crossing point of the A2+X– and A+X* potential surfaces relative to the equilibrium internuclear separation of the A+X- ground state. The condensed phase ionic excimer Cs2+F– represents the best emission properties compared to Cs2+Cl– and Rb2+F–. This is demonstrated by the B–X fluorescent transition dominating the excited state decay and also the fluorescence intensity exceeding those of Cs2+Cl– and Rb2+F– by a factor of about 6 and 20, respectively. 1. R. Sauerbrey and H. Langhoff, IEEE J. QE-21, 179 (1985). 2. N.G. Basov, M.G. Voitik, V.S. Zuev, and V.P. Kutalchov, Sov. J. Quantum Electron 15, 1455 (1985). 3. H.M.I. Bastiaens, F.T.J.L. Lankhorst, P.J.M. Peters, and W.J. Witteman, Appl. Phys. Lett. 60, 2834 (1992). 4. S. Kubodera, P.J. Wisoff, and R. Sauerbrey, J. Opt. Soc. Am. B9, 10 (1992). 5. C. Toth, J.F. Young, and R. Sauerbrey, Opt. Lett. 18, 2120 (1993). 6. T.T. Yang, V.T. Gylys, and D.G. Harris, J. Opt. Soc. Am. B6, 1536 (1989). 7. D. Xing, K. Ueda, and H. Takuma, Chem. Phys. Lett. 163, 193 (1989). 8. S. Kubodera, P.J. Wisoff, and R. Sauerbrey, J. Chem. Phys. 92, 5867 (1990). 9. S. Kubodera and R. Sauerbrey, Opt. Comm. 94, 515 (1992). 10. M. Schumann and H. Langhoff, J. Chem. Phys. 101, 4769 (1994) 11. G. Œliwiñski, Ch. Bressler, and N. Schwentner, Phys. Status Solidi B193, 247 (1996). 12. G. Œliwiñski and N. Schwentner, J. Appl. Phys. D30, 2229 (1997). 13. G. Œliwiñski and N. Schwentner, J. Low Temp. Phys. 111, 733 (1998). 14. E.S. Rittner, J. Chem. Phys. 19, 1030 (1951). 15. G. Zerza, G. Œliwiñski, and N. Schwentner, Appl. Phys. B55, 331 (1992) 16. G. Zerza, G. Œliwiñski, and N. Schwentner, Appl. Phys. A56, 156 (1993) 17. M. Frankowski, G. Œliwiñski, and N. Schwentner, SPIE Proc. 3724, 362 (1999). 18. M. Frankowski, G. Œliwiñski, and N. Schwentner, J. Low Temp. Phys. 122, 443 (2001). Luminescence and formation of alkalihalide ionic excimers in solid Ne and Ar Fizika Nizkikh Temperatur, 2003, v. 29, Nos. 9/10 1117