- Email: [email protected]
Emission spectrum and crystal field parameters of pentanitratoeuropiate(III) ions
Journal of the Less-Common Metals, 93 (1983) 241
Spin-correlated
crystal field effects in lanthanide
241
ions*
W. Y. P. FLING and D. J. NEWMAN Department of Physics, University of Hong Kong, Hong Kong (Hong Kong) Ab initio calculations of overlap and covalency contributions to the spin-correlated crystal field (SCCF) in Pr3’ with a single ligand are described. It is shown that covalency provides a positive contribution to the C~parameters describing the SCCF, thus giving a possible explanation of some characteristic experimental results. Numerical results for various types of contribution to the SCCF are tabulated.
Analysis
of the Pr3 + spectrum
C. KHAN MALEK, Laboratoire
J. C. KRUPA
de Radiochimie,
in the incommensurate
phase of ThCl,*
and M. GENET
Znstitut de Physique NuclCaire, B.P. I, 91406 Orsay Ce’dex (France)
The crystal energy level structure problem in the Pr3+ ((4f)‘) configuration is formally equivalent to that for its isoelectronic actinide ion U4’((5f)‘). The modulated and incommensurate low temperature phase of the matrix in a II“’ -doped single crystal of ThCl, produces characteristic lineshapes owing to the modulation of the crystal field. The modulation of the halide position reduces the site symmetry from D,, to D, and, as has been shown from spectral singularities, some of the U4+ impurity ions pin the phase of the modulation and remain in D,, sites. This behaviour is not obvious in the Pr-‘+-ThCl, spectra where the lineshapes are more conventional and the transitions are less intense. This is due to the fact that the protected 4f electrons are less sensitive to the crystal field manifestation than are the 5f electrons which are characterized by a greater extension of the radial wavefunction. As a consequence the crystal Stark splitting is roughly half that in II4 ‘-ThCl, and the SLJ multiplets of Pr3’ can easily be labelled because there is no significant overlapping except, possibly, in the weak lines of the ‘I, group. 34 crystal field states were identified as being associated with D,, site symmetry and were fitted to the parameters with a deviation of 29 cm- ‘. This least squares preliminary calculation leads to the following set of parameter values: ; = 724cm-‘; Fh F” = 11176cm-‘; F* = 68476cm-‘; F4 = 50743 cm-‘;
= 33483 cm- 1; B,’ = 1443 cm-‘; ; = 1534 cm-’ B,’ = 435cm-‘, ) B 4e = 415cm-’ B,“ = -476cm-‘; a = 21.20cm-’ B,“ = lOOlcm_‘; 8,112 = -55.4cm-’
Emission spectrum and crystal field parameters pentanitratoeuropiate(II1) ions*
of
J.-C. G. BUNZLI, B. KLEIN and G.-O. PRADERVAND Znstitut de Chimie Minerale et Analytique, Lausanne (Switzerland)
Uniuersite de Lausanne, place du Chateau 3, CH-1005
P. PORCHER Laboratoire des Ele’ments de Transition dans les Solides, Equipe de Recherche du CNRS 210,l place A. Briand, F-92190 Meudon Belleuue (France) * Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April 18-21, 1983. 0022.5088/83/$3.00
(’ Elsevier Sequoia/Printed
in The Netherlands
242
Journal
of the Less-Common
Metals,
93 (1983) 242
A spectroscopic investigation at 77K of finely powdered samples of A,[Eu(NO,),] with A=(C,H,),As+, (C6H.&P+ and (CH,),N+ is reported. The crystal structure of ((C,H,),As),[Eu(NO,),] reveals a ten-coordinate polyhedron which can be approximately fitted to a bicapped dodecahedron; the site symmetry of the europium(II1) ion is C, [l]. However, if the nitrate ions are assumed to occupy one coordination site, the resulting polyhedron is almost a trigonal bipyramid and this pseudosymmetry is reflected in the pattern of the emission spectrum [2]. We have attempted to reproduce the crystal field splitting by various sets of parameters using the method of descending symmetry. For ((C,H,),P),[Eu(NO,),] standard deviations of 18 cm-i and 11 cm-’ are obtained with hamiltonians of D,, and C,, symmetry respectively. The influence of the countercation on the local pseudosymmetry is discussed. 1 2
J.-C. G. Bunzli, B. Klein, G. Chapuis and K. J. Schenk, J. Inorg. Nucl. Chem., 42 (1978) 1307. J.-C. G. Bunzli and B. Klein, in G. J. McCarthy, H. B. Silber and J. J. Rhyne (eds.), The Rare Earths in Modern Science and Technology, Vol. 3, Plenum, New York, 1982, p. 97.
Photoabsorption study of bonding in some 3d-4f intermetallics other compounds* K. B. GARG, H. S. CHAUHAN, Department
of Physics,
S. G. SAXENA
University of Rajasthan,
and
and SATISH CHANDRA Jaipur
302004 (India)
3d4f intermetallics of the type R,T, (where R is a 4f metal and T is a 3d metal) are industrially important magnetic materials. The bonding in these compounds is expected to involve a decrease in the size of the R atoms and an increase in the size of the T atoms. We studied this question by making measurements on the X-ray absorption near the edge structure, particularly on the energy position of the edge and the so-called white lines, for both types of constituent atoms in these compounds. The energy shifts observed for the L,,, edges of the R constituent and for the K edge of the T constituent appear to lend support to the idea of change in the relative sizes ofthe two types of atoms. No changes have been observed in the intensities of the white lines at the L,, and the L,,, edges and in the areas under them. These are interpreted in terms of non-participation of d states in bonding. Similar photoabsorption measurements were carried out on a number of organic complexes of some rare earth metals. The results are interpreted in terms of the predominant covalent bonding in these compounds and the changes that take place in the electronic configuration of the rare earth atoms on chemical combination. The most notable result obtained for these semiconducting compounds is the appearance of a white line at the L, edge together with those observed at the L,, and L,,, edges in the metals and the intermetallic compounds. This is the first time that white lines have been simultaneously observed at all three L edges of a system. Two possible reasons are discussed for the appearance of this white line: the formation of p symmetric excitonic levels in the band gap followed by an electronic transition from the 2s state to the excitonic state, and an increase in the density of the unoccupied p symmetric states near the Fermi level owing to dehybridization and narrowing of the 6p band caused by the larger interatomic distances in the compounds. Our results support the latter explanation. The measurements were made using a 400mm bent crystal spectrograph. The intermetallic compounds were prepared by arc melting the constituents in an argon atmosphere followed by annealing and characterization using X-ray diffraction.
*Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April 18-21, 1983. 0022-5088/83/$3.00
0 Elsevier Sequoia/Printed
in The Netherlands
Spin-correlated
crystal field effects in lanthanide
241
ions*
W. Y. P. FLING and D. J. NEWMAN Department of Physics, University of Hong Kong, Hong Kong (Hong Kong) Ab initio calculations of overlap and covalency contributions to the spin-correlated crystal field (SCCF) in Pr3’ with a single ligand are described. It is shown that covalency provides a positive contribution to the C~parameters describing the SCCF, thus giving a possible explanation of some characteristic experimental results. Numerical results for various types of contribution to the SCCF are tabulated.
Analysis
of the Pr3 + spectrum
C. KHAN MALEK, Laboratoire
J. C. KRUPA
de Radiochimie,
in the incommensurate
phase of ThCl,*
and M. GENET
Znstitut de Physique NuclCaire, B.P. I, 91406 Orsay Ce’dex (France)
The crystal energy level structure problem in the Pr3+ ((4f)‘) configuration is formally equivalent to that for its isoelectronic actinide ion U4’((5f)‘). The modulated and incommensurate low temperature phase of the matrix in a II“’ -doped single crystal of ThCl, produces characteristic lineshapes owing to the modulation of the crystal field. The modulation of the halide position reduces the site symmetry from D,, to D, and, as has been shown from spectral singularities, some of the U4+ impurity ions pin the phase of the modulation and remain in D,, sites. This behaviour is not obvious in the Pr-‘+-ThCl, spectra where the lineshapes are more conventional and the transitions are less intense. This is due to the fact that the protected 4f electrons are less sensitive to the crystal field manifestation than are the 5f electrons which are characterized by a greater extension of the radial wavefunction. As a consequence the crystal Stark splitting is roughly half that in II4 ‘-ThCl, and the SLJ multiplets of Pr3’ can easily be labelled because there is no significant overlapping except, possibly, in the weak lines of the ‘I, group. 34 crystal field states were identified as being associated with D,, site symmetry and were fitted to the parameters with a deviation of 29 cm- ‘. This least squares preliminary calculation leads to the following set of parameter values: ; = 724cm-‘; Fh F” = 11176cm-‘; F* = 68476cm-‘; F4 = 50743 cm-‘;
= 33483 cm- 1; B,’ = 1443 cm-‘; ; = 1534 cm-’ B,’ = 435cm-‘, ) B 4e = 415cm-’ B,“ = -476cm-‘; a = 21.20cm-’ B,“ = lOOlcm_‘; 8,112 = -55.4cm-’
Emission spectrum and crystal field parameters pentanitratoeuropiate(II1) ions*
of
J.-C. G. BUNZLI, B. KLEIN and G.-O. PRADERVAND Znstitut de Chimie Minerale et Analytique, Lausanne (Switzerland)
Uniuersite de Lausanne, place du Chateau 3, CH-1005
P. PORCHER Laboratoire des Ele’ments de Transition dans les Solides, Equipe de Recherche du CNRS 210,l place A. Briand, F-92190 Meudon Belleuue (France) * Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April 18-21, 1983. 0022.5088/83/$3.00
(’ Elsevier Sequoia/Printed
in The Netherlands
242
Journal
of the Less-Common
Metals,
93 (1983) 242
A spectroscopic investigation at 77K of finely powdered samples of A,[Eu(NO,),] with A=(C,H,),As+, (C6H.&P+ and (CH,),N+ is reported. The crystal structure of ((C,H,),As),[Eu(NO,),] reveals a ten-coordinate polyhedron which can be approximately fitted to a bicapped dodecahedron; the site symmetry of the europium(II1) ion is C, [l]. However, if the nitrate ions are assumed to occupy one coordination site, the resulting polyhedron is almost a trigonal bipyramid and this pseudosymmetry is reflected in the pattern of the emission spectrum [2]. We have attempted to reproduce the crystal field splitting by various sets of parameters using the method of descending symmetry. For ((C,H,),P),[Eu(NO,),] standard deviations of 18 cm-i and 11 cm-’ are obtained with hamiltonians of D,, and C,, symmetry respectively. The influence of the countercation on the local pseudosymmetry is discussed. 1 2
J.-C. G. Bunzli, B. Klein, G. Chapuis and K. J. Schenk, J. Inorg. Nucl. Chem., 42 (1978) 1307. J.-C. G. Bunzli and B. Klein, in G. J. McCarthy, H. B. Silber and J. J. Rhyne (eds.), The Rare Earths in Modern Science and Technology, Vol. 3, Plenum, New York, 1982, p. 97.
Photoabsorption study of bonding in some 3d-4f intermetallics other compounds* K. B. GARG, H. S. CHAUHAN, Department
of Physics,
S. G. SAXENA
University of Rajasthan,
and
and SATISH CHANDRA Jaipur
302004 (India)
3d4f intermetallics of the type R,T, (where R is a 4f metal and T is a 3d metal) are industrially important magnetic materials. The bonding in these compounds is expected to involve a decrease in the size of the R atoms and an increase in the size of the T atoms. We studied this question by making measurements on the X-ray absorption near the edge structure, particularly on the energy position of the edge and the so-called white lines, for both types of constituent atoms in these compounds. The energy shifts observed for the L,,, edges of the R constituent and for the K edge of the T constituent appear to lend support to the idea of change in the relative sizes ofthe two types of atoms. No changes have been observed in the intensities of the white lines at the L,, and the L,,, edges and in the areas under them. These are interpreted in terms of non-participation of d states in bonding. Similar photoabsorption measurements were carried out on a number of organic complexes of some rare earth metals. The results are interpreted in terms of the predominant covalent bonding in these compounds and the changes that take place in the electronic configuration of the rare earth atoms on chemical combination. The most notable result obtained for these semiconducting compounds is the appearance of a white line at the L, edge together with those observed at the L,, and L,,, edges in the metals and the intermetallic compounds. This is the first time that white lines have been simultaneously observed at all three L edges of a system. Two possible reasons are discussed for the appearance of this white line: the formation of p symmetric excitonic levels in the band gap followed by an electronic transition from the 2s state to the excitonic state, and an increase in the density of the unoccupied p symmetric states near the Fermi level owing to dehybridization and narrowing of the 6p band caused by the larger interatomic distances in the compounds. Our results support the latter explanation. The measurements were made using a 400mm bent crystal spectrograph. The intermetallic compounds were prepared by arc melting the constituents in an argon atmosphere followed by annealing and characterization using X-ray diffraction.
*Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April 18-21, 1983. 0022-5088/83/$3.00
0 Elsevier Sequoia/Printed
in The Netherlands