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Optical characterization of BaLaALO4:Nd
Journal of Alloys and Compounds
259 ( 1997) 69-73
tica W.
Ryba-Romanowski”‘“, S. Goigb”, “Imtitute
ab
of Low Tentperature and Stntcture Research, Polish Academy of Sciences. Wrociaw. Poland hlr~.~tituteof Electronic Muteriuls Technology, Warsaw, Poland Received 13 December 1996; received in revised form 20 February 1997
Abstract Crystals of BaLaAlO, and BaLaAlO,:Nd were obtained by the Czochralski method from a stoichiometric melt. X-ra!l studies indicated that the crystal lattice is orthorhombic and ordered, whereas the bandwidths of spectral lines corresponding to transitions between individual crystal field levels of Nd’ ’ were as large as those encountered in disordered structures. Examination with an electron microscope revealed that the material is composed of crystalline phase consistent with the X-ray data and a fully amorphous ase. 0 1997 Elsevier Science S.A. Ke,wwd~:
Crystal .gow4x Optical properties; Phololuminc.4cerlce .-_
Among a variety B,O,-C,O,
of compounds
system (A=Ca,
derived
Sr,
from the AO-
Ba;
on
C = Al. Ga, transition metal A CO., (A ==Ca, Sr) have been crystals tit’ composition obtui& r~cntly by the Czoshralski method und considcreel ils substrata for high tcmpcraturc sup~rconclu~titlg IillllS 1l-31 01’Iuniincsccnt IlIiltd’Ki;llS i\scclIGlIcd thut A CO, co~~~~~~)ilnds 1 tetragonal crystuls within slx~cc groa structure is built up s of GO, octahedra and between the layers the A an atoms occupy randomly
of
element;
y giving
on the crystal growth, these
to certain
system are not
,0,&Y$13
knowledge
rise
crystals
is
stability
operties
of
limited.
&,aAIO,
were obt‘lined for the first
region and Crystals
of
time by :I slow
cooling of the stoichio the crystals of BaLaGa the same ~~ettl(~d 18J. found to be orthorhot
nearest surrounding
1’71.
“Corresponding author
09258388/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PfI SO925-8388(97)00121-7
evalua!e
interest.
their
rare
ea
reached a 1eng:h of 40 mm and diameter of 18 mm. The structure of crystals was examined by X-ray measurements. Nd content in doped crystal was checked by chemical analysis, in which small quantities of a crystal were dissolved in I-INO, and the obtained solutions were examined by inductively coupled plasma emission (I.C.P.). the samples, in the form of For optical measuremenis. cut out from spheres and plates 6X4X I mm’,were polished. Three oriented samples for each cryzcal were prepared with their edges parallel to the axes of the crystal and with a large surface perpendicular to n, b and c axis respectively. Optical absorption spectra were measured with a Varian Model 2300 spectrophotometer at room temperature and at 5 K. Ltiminescence spectra wer? excited by an argon ion laser, dispersed by an l-m grating monochromator and detected by a cooled photomultiplier with a S-l spectral response. Resulting signals were processed by a SRS250 boxcar averager and stored. In luminescence lifetime medbtirements, a nitrogen laser pumped dye laser was used as an excitation source. For low temperature measurements, the samples were installed in a CF1204 continuous flow helium cryostat equipped with a temperature controller.
An undoped BLA crystal and a crystal with nominal Nd concentration of 1 mol% were grown for this study. Chemical analysis revealed that the distribution of Nd in doped crysial is uniform, but the actual concentration is only 0.43 mol%. Structure of crystals was verified by X-ray examination. The lattice constants were found to be n =0.98837 n m, b=0.72855 nm, c=O.58328 nm, in agreement with those reported earlier for crystals obtained by cooling of stoichiometric melt [il. To the eye, the colour of undoped and Nd doped BLA IS similar. l3oth crystals display intense yellow tint, the neodymium content being too low to make a difference. It has been noted previously that the BaLaGaO, crystals were orange [S]. Thus, it appears that t colouring is a common feature of orthorhombic and ragonal ABCO, crystals, since the latter ones display various colours from light yellow to dark red erally believed that the structural defects oxygen vacancies in tetragonal ABCO, are r this feature [2,3,6], however the nature of the defects are not identified yet. Optical absorption associated with defect centres can be seen in Fig. 1 which
Wavenumber [cm-‘] 18000
Wavelen Fig. 1. Survey absorption spectndof Nd“
in iiaEaAiG,
. .Inset shows absorption of undoped BaLaAIU,
12Ot?
15000
I
recorded at room temperature with unpolarized light propagating along three axes of the crystal.
crystal 0.2-mm thick.
IN. R~h~-Rnttruttorr,ski
et ~1. I Jaurtt~tl
shows a survey of absorptiorr specua of BLA:Nd recorded at room temperature with light propagating along a, b and c axis. In addition to several sharp lines corresponding to transitions of Nd3’, there is a broad absorption band beginning at about 500 nm and stretching up to the fundamental absorption edge of BLA at about 240 nm. In order to locate the absorption edge, a sample of undoped BLA 0.2-mm thick was prepared and its absorption to UV was recorded at room temperature. The obtained spectrum is shown in the inset of Fig. 1. Intensities of Nd’* absorption recorded with light propagating along a, b and c axis of the crystal are slightly different. Corresponding oscillator strengths evaluated by numerical integration of absorption bands are given in three columns of Table 1. In fourth column of this tabtc, the oscillator strengths P,,, are presented. They were evaluated from spectrum which was recorded with a sample composed of three plates with (loo), (010) and (001) orientations respectively. It has been suggested [lo] that such ‘isotropic’ oscillator strengths should be used for the uc~1a1Judd-Ofelt analysis of absorption spectra recorded with anisotropic media. In the last column of Table 1, we present the values of oscillator strengths evaluated by a !esst squares fit between experimental P,,, and theoretical IPtheorexpressed in terms of adjustable 0 parameters and matrix elemerts of unit tensor operators. Three parameters fiz = 1.4* lo-” cm’, fi~=3.8*‘10-‘” cm’ and .f&,=3.7*t&‘” cm’ derived from this procedure were next used to calculate the rates A of radiative transitions from the JF,,2 hrminescent level to all lower lying levels aa well as the corresponding lu cence branching ratios /3. The refractive index of BaLaAlO, WRS not determined earlier. Using the method of refraction in oriented prism we determined the edium value of refractive index II= 1.799. which was used to calculate the r&es A. Calculated values o Table 2. The radiative ltfctime of tne ‘F3,_, . an mverb;L of the total ra tive transition rate is whereas the luminescence etime was found to be from an analysis of lu difference between t e calculated and ex time is higher than the estimated error of lifetime measurements of 10%. Contribution of the multiphonon relaxation to the &cay is believed to be negligible since the ex-
Table
Cotnpolrtlds 259 (1997)
69- 7-3
71
Table 2 Calculated radiative transition rates A, luminescence branching ratios /3 and resulting radiative lifetime 7 for the ‘FIIZ level of Nd”
in BaLaAlO,
crystal [L’. S’]J’ J--
,,,+41‘,,2
A (p-m)
4 (s-l)
0.88
1343
0.42
--%Z
1.06
1591
0.47
-+Q, a/?
I .33
324
0.10
--%~
I .88
17
0.01
t-
7 (t.W
P
297
perimental luminescence lifetime -&as f&and to be independent of temperature in the 5-3 region. The discrepancy may be ue to the i~ce~itude i the determination of the Nd content in the sample. Additional source of error is a scarcity of data available for
Wavelength [nm] 920
10800
108OQ
900
880
l~QQ0
41
Fig. 2. Luminescence spectra associated with the ‘IF,, ,- ‘I.,, NJ”
860
, transmon
of
at 300 K and at 5 K.
I
Mtxlhured and ckulated Excited level
oxillator
\trengrh\
of Nd’
Average wacenumber (cm
.a l--
of A1h.w and
r/2
JF ‘H,,,, S,?’ J-I-%,,
’ in ,BtiLaAIO,
at 3W K: 311 tranbltions are from the ‘I<,,? level to the level indlcatcd _P
O.scdlator :>tringth Px lO^ -(001)
(010)
‘)
P *I\L.
P , .,I
I I 320
I .57
I.54
2.43
I .93
2.04
12 254
5.59
7.07
9.21
6.95
6.20
13 24s
4.99
5.66
6.9 I
5.87
6.34
9X8
9.15
8.36
10.52
8.86
8 .&& ‘9
18 981
4.11
3.06
3.81
3.19
4.33
-
712. %d
‘K
%&
(/?’ ‘G,,,. I I/?.
IG
G,,,,
72
Wavelength [nm]l 1080
9200
1060
9400
Wavenumber
[cm-’
9600
the Judd-Ofelt treatment since only 5 absorption bands of Nd3’ lie outside the band associated with the host absorption. Luminescence spectra associated with the 4FI,I-419,1 z transitions recorded at room temperature and ?,,,-‘I,,, and at 5 K are shown in Figs. 2 and 3 respectively. Room temperature spectra consist of poorly resolved bands which are formed by overlapping transitions between individual crystal field levels of initial and terminal multiplets. In low temperature spectra, the transitions originate in the lowest multiplet and all crystal field component of the ‘F,,, components of the terminal ‘I,,, and “I, t ,? multiplets may be located. Their energies and the splitting of several excited multiplets determined from 5 K absorption spectra are given in Table 3. It can be seen in Table 3 that the from optical spectra number of crystal field levels derive for all multiplets does not exceed the expected one, indicating that Nd ions enter only one type of site. On the other hand, the lines associated with transitions between individual crystal field levels are asymmetric and relatively broad. Their band widths are comprised between 25 and 100 cm ’ FWt-fM, both in emission and absorption spectra
!*IK. -8. High IYW~U~I~II &xtron mtcroscopemicrographof BaLoAlO, showing ordered crystalline phase and amorphousphase. Inset shows a sclectrd area difktction of cryatllitte phase.
W. R~ha-Rotmtlo,vsAi
et ul. I hurturl
recorded at 5 K. Similar bandwidths were encountered in rare earth doped tetragonal ABCO, crystals where a structural disorder induces a strong inhomogeneous line broadening, but they are surprisingly large in ordered lattice of orthorhombic BLA. In order to find out about the cause of the spectral line broadening a sample of crystal was ground to get a fine powder and individual grains were examined using a Philips CM-20 electron microscope working in the transmission mode. A photograph in Fig. 4 shows one of typical pictures obtained with our samples. It can be seen that the nomina!ly single crystal sample consists of ordered crystalline phase imbedded in an amorphous medium. Selected area diffractions are consistent with this observation and contain patterns corresponding to crystalline and amorphous phases. The inset in Fig. 4 shows a selected area diffraction corresponding to the crystalline phase. It should be noted that in optical absorption and emission measurements the Nd’+ ions in both the amorphous and crystalline phases are excited simultaneously. Resulting spectra do not contain additional lines, therefore the tirst coordination sphere of Nd’+ ion in both the phases appears to be very similar. Occurrence of amorphous phase in very slowly solidified compounds, which do not contain the glass forming oxides is rather puzzling and needs to be investigated in greater detail. Further processes of solidification LA are being prepared now in order to explain the
of Allo_vs atId Cotttpouttd.~ 259 (1997) 69- 73
13
The authors thank Dr. L. K.rajczyk for an exami samp!es with an electron microscope.
3. Konopka.
1. Wolf& IEEE Trans. MTT
40 (1992)
24.
R.D. Shannon. R.A. Oswald, J.B. Parise, B.H.T. Cnai, P Byszewski. A. Pajqczkowska. A. Dabkowski. I32
( 1993)
R. Sobolewski, J. SQI. State Chem. 98 (1992) 98. H.A.
Dabkowska.
E.F. Kustov. VP. Petrol. (a) 41 (1977)
J. Cryst. Growth
D.S. Petrova. J.P. Udalov, Phys. Stat. Sol.
379.
W. Ryba-Romanowski, Dominiak-Dzik. 217 (1995)
J.E. Greedan,
205.
S. Golqb.
1. Sokhlska. W.A.
A. Pajqczkowska. M. Berkowski.
Plsarski. 6.
J. Alloys Comp.
263.
J.C. Souriau. C. Borei, Ch. Wyon. C. Li. R. Moncorge, J. Lumin. 59
( 1994)
349.
L.M. Kovba. L.V. Lykova. E.V. Antipov. Koord. #him. 1. Riiter. Hk. Miiller-Buxzhbaum.
II
( 1985) 74. ( 1990)
Z. Anorg. AlIp. Chem. 584
I Is). A. Gloubokov. Res. Bull. 31
A. Klos, J. Fink-Finowicki,
( 1996)
A. Pajgczkowska. Mater.
271. Silvestrova. SE.
Phys. Stat. Sol. (a) 80 (1983)
607.
Sarhisov. G.A.
259 ( 1997) 69-73
tica W.
Ryba-Romanowski”‘“, S. Goigb”, “Imtitute
ab
of Low Tentperature and Stntcture Research, Polish Academy of Sciences. Wrociaw. Poland hlr~.~tituteof Electronic Muteriuls Technology, Warsaw, Poland Received 13 December 1996; received in revised form 20 February 1997
Abstract Crystals of BaLaAlO, and BaLaAlO,:Nd were obtained by the Czochralski method from a stoichiometric melt. X-ra!l studies indicated that the crystal lattice is orthorhombic and ordered, whereas the bandwidths of spectral lines corresponding to transitions between individual crystal field levels of Nd’ ’ were as large as those encountered in disordered structures. Examination with an electron microscope revealed that the material is composed of crystalline phase consistent with the X-ray data and a fully amorphous ase. 0 1997 Elsevier Science S.A. Ke,wwd~:
Crystal .gow4x Optical properties; Phololuminc.4cerlce .-_
Among a variety B,O,-C,O,
of compounds
system (A=Ca,
derived
Sr,
from the AO-
Ba;
on
C = Al. Ga, transition metal A CO., (A ==Ca, Sr) have been crystals tit’ composition obtui& r~cntly by the Czoshralski method und considcreel ils substrata for high tcmpcraturc sup~rconclu~titlg IillllS 1l-31 01’Iuniincsccnt IlIiltd’Ki;llS i\scclIGlIcd thut A CO, co~~~~~~)ilnds 1 tetragonal crystuls within slx~cc groa structure is built up s of GO, octahedra and between the layers the A an atoms occupy randomly
of
element;
y giving
on the crystal growth, these
to certain
system are not
,0,&Y$13
knowledge
rise
crystals
is
stability
operties
of
limited.
&,aAIO,
were obt‘lined for the first
region and Crystals
of
time by :I slow
cooling of the stoichio the crystals of BaLaGa the same ~~ettl(~d 18J. found to be orthorhot
nearest surrounding
1’71.
“Corresponding author
09258388/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PfI SO925-8388(97)00121-7
evalua!e
interest.
their
rare
ea
reached a 1eng:h of 40 mm and diameter of 18 mm. The structure of crystals was examined by X-ray measurements. Nd content in doped crystal was checked by chemical analysis, in which small quantities of a crystal were dissolved in I-INO, and the obtained solutions were examined by inductively coupled plasma emission (I.C.P.). the samples, in the form of For optical measuremenis. cut out from spheres and plates 6X4X I mm’,were polished. Three oriented samples for each cryzcal were prepared with their edges parallel to the axes of the crystal and with a large surface perpendicular to n, b and c axis respectively. Optical absorption spectra were measured with a Varian Model 2300 spectrophotometer at room temperature and at 5 K. Ltiminescence spectra wer? excited by an argon ion laser, dispersed by an l-m grating monochromator and detected by a cooled photomultiplier with a S-l spectral response. Resulting signals were processed by a SRS250 boxcar averager and stored. In luminescence lifetime medbtirements, a nitrogen laser pumped dye laser was used as an excitation source. For low temperature measurements, the samples were installed in a CF1204 continuous flow helium cryostat equipped with a temperature controller.
An undoped BLA crystal and a crystal with nominal Nd concentration of 1 mol% were grown for this study. Chemical analysis revealed that the distribution of Nd in doped crysial is uniform, but the actual concentration is only 0.43 mol%. Structure of crystals was verified by X-ray examination. The lattice constants were found to be n =0.98837 n m, b=0.72855 nm, c=O.58328 nm, in agreement with those reported earlier for crystals obtained by cooling of stoichiometric melt [il. To the eye, the colour of undoped and Nd doped BLA IS similar. l3oth crystals display intense yellow tint, the neodymium content being too low to make a difference. It has been noted previously that the BaLaGaO, crystals were orange [S]. Thus, it appears that t colouring is a common feature of orthorhombic and ragonal ABCO, crystals, since the latter ones display various colours from light yellow to dark red erally believed that the structural defects oxygen vacancies in tetragonal ABCO, are r this feature [2,3,6], however the nature of the defects are not identified yet. Optical absorption associated with defect centres can be seen in Fig. 1 which
Wavenumber [cm-‘] 18000
Wavelen Fig. 1. Survey absorption spectndof Nd“
in iiaEaAiG,
. .Inset shows absorption of undoped BaLaAIU,
12Ot?
15000
I
recorded at room temperature with unpolarized light propagating along three axes of the crystal.
crystal 0.2-mm thick.
IN. R~h~-Rnttruttorr,ski
et ~1. I Jaurtt~tl
shows a survey of absorptiorr specua of BLA:Nd recorded at room temperature with light propagating along a, b and c axis. In addition to several sharp lines corresponding to transitions of Nd3’, there is a broad absorption band beginning at about 500 nm and stretching up to the fundamental absorption edge of BLA at about 240 nm. In order to locate the absorption edge, a sample of undoped BLA 0.2-mm thick was prepared and its absorption to UV was recorded at room temperature. The obtained spectrum is shown in the inset of Fig. 1. Intensities of Nd’* absorption recorded with light propagating along a, b and c axis of the crystal are slightly different. Corresponding oscillator strengths evaluated by numerical integration of absorption bands are given in three columns of Table 1. In fourth column of this tabtc, the oscillator strengths P,,, are presented. They were evaluated from spectrum which was recorded with a sample composed of three plates with (loo), (010) and (001) orientations respectively. It has been suggested [lo] that such ‘isotropic’ oscillator strengths should be used for the uc~1a1Judd-Ofelt analysis of absorption spectra recorded with anisotropic media. In the last column of Table 1, we present the values of oscillator strengths evaluated by a !esst squares fit between experimental P,,, and theoretical IPtheorexpressed in terms of adjustable 0 parameters and matrix elemerts of unit tensor operators. Three parameters fiz = 1.4* lo-” cm’, fi~=3.8*‘10-‘” cm’ and .f&,=3.7*t&‘” cm’ derived from this procedure were next used to calculate the rates A of radiative transitions from the JF,,2 hrminescent level to all lower lying levels aa well as the corresponding lu cence branching ratios /3. The refractive index of BaLaAlO, WRS not determined earlier. Using the method of refraction in oriented prism we determined the edium value of refractive index II= 1.799. which was used to calculate the r&es A. Calculated values o Table 2. The radiative ltfctime of tne ‘F3,_, . an mverb;L of the total ra tive transition rate is whereas the luminescence etime was found to be from an analysis of lu difference between t e calculated and ex time is higher than the estimated error of lifetime measurements of 10%. Contribution of the multiphonon relaxation to the &cay is believed to be negligible since the ex-
Table
Cotnpolrtlds 259 (1997)
69- 7-3
71
Table 2 Calculated radiative transition rates A, luminescence branching ratios /3 and resulting radiative lifetime 7 for the ‘FIIZ level of Nd”
in BaLaAlO,
crystal [L’. S’]J’ J--
,,,+41‘,,2
A (p-m)
4 (s-l)
0.88
1343
0.42
--%Z
1.06
1591
0.47
-+Q, a/?
I .33
324
0.10
--%~
I .88
17
0.01
t-
7 (t.W
P
297
perimental luminescence lifetime -&as f&and to be independent of temperature in the 5-3 region. The discrepancy may be ue to the i~ce~itude i the determination of the Nd content in the sample. Additional source of error is a scarcity of data available for
Wavelength [nm] 920
10800
108OQ
900
880
l~QQ0
41
Fig. 2. Luminescence spectra associated with the ‘IF,, ,- ‘I.,, NJ”
860
, transmon
of
at 300 K and at 5 K.
I
Mtxlhured and ckulated Excited level
oxillator
\trengrh\
of Nd’
Average wacenumber (cm
.a l--
of A1h.w and
r/2
JF ‘H,,,, S,?’ J-I-%,,
’ in ,BtiLaAIO,
at 3W K: 311 tranbltions are from the ‘I<,,? level to the level indlcatcd _P
O.scdlator :>tringth Px lO^ -(001)
(010)
‘)
P *I\L.
P , .,I
I I 320
I .57
I.54
2.43
I .93
2.04
12 254
5.59
7.07
9.21
6.95
6.20
13 24s
4.99
5.66
6.9 I
5.87
6.34
9X8
9.15
8.36
10.52
8.86
8 .&& ‘9
18 981
4.11
3.06
3.81
3.19
4.33
-
712. %d
‘K
%&
(/?’ ‘G,,,. I I/?.
IG
G,,,,
72
Wavelength [nm]l 1080
9200
1060
9400
Wavenumber
[cm-’
9600
the Judd-Ofelt treatment since only 5 absorption bands of Nd3’ lie outside the band associated with the host absorption. Luminescence spectra associated with the 4FI,I-419,1 z transitions recorded at room temperature and ?,,,-‘I,,, and at 5 K are shown in Figs. 2 and 3 respectively. Room temperature spectra consist of poorly resolved bands which are formed by overlapping transitions between individual crystal field levels of initial and terminal multiplets. In low temperature spectra, the transitions originate in the lowest multiplet and all crystal field component of the ‘F,,, components of the terminal ‘I,,, and “I, t ,? multiplets may be located. Their energies and the splitting of several excited multiplets determined from 5 K absorption spectra are given in Table 3. It can be seen in Table 3 that the from optical spectra number of crystal field levels derive for all multiplets does not exceed the expected one, indicating that Nd ions enter only one type of site. On the other hand, the lines associated with transitions between individual crystal field levels are asymmetric and relatively broad. Their band widths are comprised between 25 and 100 cm ’ FWt-fM, both in emission and absorption spectra
!*IK. -8. High IYW~U~I~II &xtron mtcroscopemicrographof BaLoAlO, showing ordered crystalline phase and amorphousphase. Inset shows a sclectrd area difktction of cryatllitte phase.
W. R~ha-Rotmtlo,vsAi
et ul. I hurturl
recorded at 5 K. Similar bandwidths were encountered in rare earth doped tetragonal ABCO, crystals where a structural disorder induces a strong inhomogeneous line broadening, but they are surprisingly large in ordered lattice of orthorhombic BLA. In order to find out about the cause of the spectral line broadening a sample of crystal was ground to get a fine powder and individual grains were examined using a Philips CM-20 electron microscope working in the transmission mode. A photograph in Fig. 4 shows one of typical pictures obtained with our samples. It can be seen that the nomina!ly single crystal sample consists of ordered crystalline phase imbedded in an amorphous medium. Selected area diffractions are consistent with this observation and contain patterns corresponding to crystalline and amorphous phases. The inset in Fig. 4 shows a selected area diffraction corresponding to the crystalline phase. It should be noted that in optical absorption and emission measurements the Nd’+ ions in both the amorphous and crystalline phases are excited simultaneously. Resulting spectra do not contain additional lines, therefore the tirst coordination sphere of Nd’+ ion in both the phases appears to be very similar. Occurrence of amorphous phase in very slowly solidified compounds, which do not contain the glass forming oxides is rather puzzling and needs to be investigated in greater detail. Further processes of solidification LA are being prepared now in order to explain the
of Allo_vs atId Cotttpouttd.~ 259 (1997) 69- 73
13
The authors thank Dr. L. K.rajczyk for an exami samp!es with an electron microscope.
3. Konopka.
1. Wolf& IEEE Trans. MTT
40 (1992)
24.
R.D. Shannon. R.A. Oswald, J.B. Parise, B.H.T. Cnai, P Byszewski. A. Pajqczkowska. A. Dabkowski. I32
( 1993)
R. Sobolewski, J. SQI. State Chem. 98 (1992) 98. H.A.
Dabkowska.
E.F. Kustov. VP. Petrol. (a) 41 (1977)
J. Cryst. Growth
D.S. Petrova. J.P. Udalov, Phys. Stat. Sol.
379.
W. Ryba-Romanowski, Dominiak-Dzik. 217 (1995)
J.E. Greedan,
205.
S. Golqb.
1. Sokhlska. W.A.
A. Pajqczkowska. M. Berkowski.
Plsarski. 6.
J. Alloys Comp.
263.
J.C. Souriau. C. Borei, Ch. Wyon. C. Li. R. Moncorge, J. Lumin. 59
( 1994)
349.
L.M. Kovba. L.V. Lykova. E.V. Antipov. Koord. #him. 1. Riiter. Hk. Miiller-Buxzhbaum.
II
( 1985) 74. ( 1990)
Z. Anorg. AlIp. Chem. 584
I Is). A. Gloubokov. Res. Bull. 31
A. Klos, J. Fink-Finowicki,
( 1996)
A. Pajgczkowska. Mater.
271. Silvestrova. SE.
Phys. Stat. Sol. (a) 80 (1983)
607.
Sarhisov. G.A.