Synthesis of functionalized materials using aryloxo-organometallic compounds toward spinel-like MM′2O4 (M = Ba 2+, Sr2+; M′ = In3+, Al3+) double oxides

Article abstract of DOI:10.1021/ic301218v

The predesigned single-source precursors [Ba{(μ-ddbfo) ₂InMe₂}₂] (1), [Me₂In(μ-ddbfo)] ₂ (2), [Sr{(μ-ddbfo)₂AlMe₂}₂] (4), and [Me₂Al(μ-ddbfo)]₂ (

Full text of DOI:10.1021/ic301218v

Article
pubs.acs.org/IC
Synthesis of Functionalized Materials Using Aryloxo-Organometallic
2
+
2+
3+
Compounds toward Spinel-like MM′ O (M = Ba , Sr ; M′ = In ,
2
4
3+
Al ) Double Oxides
†
†
†
‡
,†
Łukasz John, Magdalena Kosins
†
́
̈
́
ka-Klahn, Lucjan B. Jerzykiewicz, Leszek Kępinski, and Piotr Sobota*
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
‡
Institute of Low Temperature and Structural Researches, Polish Academy of Sciences in Wrocław, 2 Okol
́
na, 50-422 Wrocław,
Poland
*
S Supporting Information
ABSTRACT: The predesigned single-source precursors [Ba-
{
(μ-ddbfo) InMe } ] (1), [Me In(μ-ddbfo)] (2), [Sr{(μ-
2 2 2 2 2
ddbfo) AlMe } ] (4), and [Me Al(μ-ddbfo)] (5) (ddbfoH =
2
2
2
2
2
2
,3-dihydro-2,2-dimethylbenzofuran-7-ol) for spinel-like dou-
ble oxides and group 13 oxide materials were prepared via the
direct reaction of the homoleptic aryloxide [M(ddbfoH) ]-
4
2
+
2+
(
ddbfo) ·ddbfoH (M = Ba , Sr (3)) and InMe or AlMe in
2
3
3
toluene. In all of the reactions, there was an organometallic-
driven abstraction of the OH protons from the 7-
benzofuranols in the Ba and Sr cation sphere. All
2
+
2+
1
compounds were characterized by elemental analysis,
H
NMR, and FT-IR spectroscopy. In addition, the molecular
structures of 1, 2, and 3 were determined by single-crystal X-ray diffraction. The oxide products derived from the compounds
mentioned above were studied using elemental analysis, Raman spectroscopy, X-ray powder diffraction, and scanning and
transmission electron microscopy equipped with an energy-dispersive spectrometer. Moreover, their specific surface area and
mesopore size distribution were evaluated using nitrogen porosimetry. Preliminary investigations of the Eu-doped SrAl O and
2
4
In O phosphors revealed that the oxides obtained could be considered as matrices for lanthanide ions.
2
3
1
9
INTRODUCTION
absorption, in lighting as a component of sodium vapor
■
20
lamps, and in health and medical applications, where it is used
The structure and properties of spinel-like oxides have attracted
considerable attention in recent years from both engineers and
21
as a material in hip replacements. Furthermore, alumina is used
as a dosimeter for radiation protection and in other therapeutic
applications for its optically stimulated luminescence properties.
In view of the wide range of applications mentioned above for
oxides, there is a strong impetus to seek out novel and
inexpensive methods for their synthesis. Classically, mixed-
cation oxide ceramics are synthesized according to conventional
solid-state reactions involving oxides, carbonates, or nitrates at
relatively high temperatures (∼1500 °C). These procedures are
largely inefficient and often lead to inhomogeneous byproduct
with poor control over the stoichiometry and phase purity.
These disadvantages have led to the rapid development of new
preparation techniques involving specific precursors. Metal
alkoxides and aryloxides represent a very important group of such
precursors, especially those that have strictly defined metal
1
scientists. These materials possess interesting magnetic and
2
electronic properties and are suitable for numerous techno-
3
logical applications, including magnetic core materials, super-
4
,5
conductors, high-frequency devices, cathode materials for
6
7
commercially available batteries, semiconductors, and gas
8
sensors, and they also constitute efficient oxide networks for
9
luminescent materials. Strontium and barium aluminates, for
example, represent some of the most studied and efficient host
materials for long-lasting phosphorescence, and their synthesis
and optical properties have been extensively explored during the
22
1
0−12
past decades.
Similarly, calcium aluminate has been used as
23
1
3
a hydraulic material in the cement industry and also in high-
strength and high-toughness ceramic/polymer composites.
Group 13 oxides, on the other hand, such as Al O , Ga O , and
14
2
3
2
3
2
4,25
stoichiometries on the molecular level.
Thus, they already
In O , are important components of spinel materials. For
2
3
have metal−oxygen bonds established, and their thermal
decomposition can be performed at relatively low temperatures
in contrast to solid-state reactions. Moreover, oxide ceramics
example, indium oxide has been extensively investigated for its
15
semiconducting properties and is commonly used in several
microelectronic areas, including window heaters, liquid crystal
16
17,18
displays, solar cells, and gas sensors.
Moreover, the
widespread occurrence of Al O is strongly emphasized in the
Received: June 7, 2012
2
3
industry, where it is used as a catalyst and catalyst support in gas
Published: August 29, 2012
©
2012 American Chemical Society
9820
dx.doi.org/10.1021/ic301218v | Inorg. Chem. 2012, 51, 9820−9832

Inorganic Chemistry
Article
derived from these materials are highly phase-pure and possess
with an ARL model 3410 + ICP spectrometer (Fissions Instruments)
and VarioEL III CHNS (in-house). Thermal decompositions were
performed using an NT 1313 furnace with thermostat KXP3+
production NEOTHERM. Samples were thermolyzed in an atmosphere
of air. The thermolyzed products were characterized by recording their
X-ray powder diffraction (PXRD) patterns with a Bruker D8 Advance
specific properties such as high levels of hardness, chemical and
23
mechanical resistance, and thermal stability. As a consequence,
these materials are perfect candidates for sol−gel and metal−
organic chemical vapor-phase deposition (MOCVD) conversion
to the appropriate metal oxides.
diffractometer using Cu K radiation (λ = 1.5418 Å). The measurements
α
Metal alkoxides and aryloxides are almost as common in
today’s chemistry as any other simple inorganic compounds and
represent an enormous family of species with broad structural
diversity. In the literature, the population of structurally
characterized heterobimetallic complexes of heavier alkaline-
were performed for 2θ = 5−120° with 2θ step = 0.008° and a 1 s
counting time. Raman spectra were recorded on a LabRam HR800
spectrophotometer. Microscope analyses were performed with a Philips
SEM 515 microscope equipped with an EDAX 9800 spectrometer (30
2
kV, linear resolution 5 nm) and TEM FEI Tecnai G 20 X-TWIN.
26
Physisorption studies were conducted using an ASAP 2020 accelerated
surface area and porosimetry system. Photoluminescence spectra were
recorded using an FSL920 spectrofluorometer from Edinburgh
Instruments with a 450 W Xe lamp and PMT operating within a
earth and group 13 metals is not significantly large. This list
includes some alkoxo, alkoxo-hydride, and alkoxo-organo-
metallic compounds that constitute so-called single-source
precursors (SSPs) for spinel-like double oxides. For example,
Veith and co-workers reported the well-defined volatile
1
85−870 nm range. The luminescence spectra were collected with a
resolution of 0.2 nm.
t
27
hydridoalkoxide [Mg{(O Bu) AlH } ]. Kessler et al. also
[Ba{(μ-ddbfo) InMe } ] (1) and [Me In(μ-ddbfo)] (2). A Schlenk
2
4
2
2
2 2
2
2
3
6
obtained a new class of heteroleptic divalent metal−aluminum
flask was charged with [Ba(ddbfoH) ](ddbfo) ·ddbfoH (0.76 g; 0.59
4 2
i
alkoxide complexes [MAl (acac) (O Pr) (OAc)] (M = Co, Zn;
mmol) and toluene (15 mL), and the resulting clear, colorless solution
was stirred vigorously and cooled to −78 °C. A 2.13 M solution of InMe
2
3
4
28
acac = acetylacetone; OAc = acetate). Another example
3
in toluene (1.9 mL; 4.05 mmol) was then added to the mixture in a
dropwise manner. Following 72 h of agitation at room temperature,
workup provided two types of colorless crystals: blocks of 1 and needles
of 2. The significant differences in size and crystal morphology allowed
us to isolate the two types. The crystals were separated under an
atmosphere of N2 using a Pasteur pipet. Anal. Calcd for 1,
C H BaIn O (1079.89): C, 48.94; H, 5.23; Ba, 12.72. Found: C,
reported in the literature involved a nickel−aluminum
i
29
[
NiAl (acac) (O Pr) ] compound. In our research group, we
2 4 4
30
have also obtained some calcium− and barium−aluminum,
3
1
barium−gallium, and group 2/group 4 alkoxo- and aryloxo-
organometallic compounds, which are perfect candidates for
3
2−34
double oxides.
We have shown that coordinated alcohol
44
56
2
8
molecules that possess a hydroxyl group at the metal site are
perfect anchors for organometallic moieties because they bring
metal atoms close to one another and have a fixed ratio for metals
48.07; H, 5.20; Ba, 13.01. Anal. Calcd for 2, C H O In (616.18): C,
24 34 4 2
46.78; H, 5.57; In, 37.27. Found: C, 46.83; H, 5.56; In, 37.25. FT-IR of 1
−1
(
cm , Nujol mull): 1878 (vw), 1698 (vw), 1610 (vs), 1590 (m), 1476
vs), 1312 (vs), 1285 (s), 1234 (m), 1190 (m), 1164 (m), 1128 (s),
35
(
depending on the oxide used. The driving force for this reaction
was the organometallic-driven abstraction of the hydroxyl
protons from the alcohol groups attached to the metal sphere.
During the initial phases of our approach, we were interested in
using the valuable features of barium and strontium aryloxides
1
110 (m), 1058 (m), 1034 (s), 971 (vw), 874 (s), 838 (w), 774 (s), 763
(
(
vs), 752 (s), 721 (s), 617 (m), 598 (m), 574 (s), 539 (m), 488 (m), 468
m), 368 (w). FT-IR of 2 (cm , Nujol mull): 1881 (vw), 1700 (vw),
−1
1
613 (vs), 1577 (m), 1484 (vs), 1310 (vs), 1285 (s), 1231 (m), 1200
(m), 1164 (m), 1129 (s), 1111 (m), 1057 (m), 1030 (s), 965 (vw), 867
2+
36 2+
[
M(ddbfoH) ](ddbfo) ·ddbfoH (M = Ba , Sr (3)). Herein,
4 2
(s), 838 (w), 777 (s), 764 (vs), 750 (s), 719 (s), 621 (m), 601 (m), 574
1
we report the results of our recent studies involving the synthesis
of a series of novel aryloxo-organometallics, including barium−
indium [Ba{(μ-ddbfo) InMe } ] (1), indium [Me In(μ-
(s), 541 (m), 491 (m). H NMR of 1 (C D CD , 298 K): δ 6.14−5.93
6
5
3
1
3
(m, 3H of Ph); 2.16 (s, CH ). C
NMR of 1 (C D CD , 298 K): δ 148.7 (s, (C(O ))C(O)), 146.7 (s,
phenoxo
); 0.68 (s, 2CH
); −0.21 (s, 2In−CH
2
3
3
6
5
3
2
2
2
2
C(Ophenoxo), 126.2 (s, C(H)C(CH )), 122.4 (s, (CH)CH(CH)), 115.8
ddbfo)] (2), strontium−aluminum [Sr{(μ-ddbfo) AlMe } ]
2
2
2
2 2
(
4
(
2
s, (CH)CH(C)), 114.1 (s, C(Ophenoxo)CH(CH)), 88.5 (s, C(CH ) ),
3 2
(
4), and aluminum [Me Al(μ-ddbfo)] (5) complexes (ddbfoH
2 2
1
3.9 (s, CH ), 28.2 (s, 2CH ), −3.1 (s, 2Al-CH ). H NMR of 2
2
3
3
=
2,3-dihydro-2,2-dimethylbenzofuran-7-ol). Such an approach
C D CD , 298 K): δ 7.11 − 6.58 (m, 3H of Ph), 2.44 (s, CH ), 1.02 (s,
6
5
3
2
allowed for the construction of compounds possessing the
predesigned molecular structure for the generation of BaIn O ,
CH ), −0.20 (s, 2In−CH ). Purity of BaIn O (%): C, 0.03; H, 0.00.
3
3
2
4
2
4
EDS: Ba/In = 0.5 (±0.01). Purity of In O (%): C, 0.00; H, 0.00. Raman
2 3
1
−
In O , SrAl O , and Al O oxides and attractive matrices for Eu-
2
3
2
4
2
3
(cm ) of BaIn O : 75 (vs), 126 (m), 192 (m), 253 (m), 304 (m), 346
2 4
doped phosphors. All of these findings will be described in detail
in this research paper.
(m), 378 (vw), 424 (m), 466 (vs), 551 (m), 610 (m), 680 (m), 846 (m),
−1
992 (w). Raman (cm ) of In
s), 132 (vs), 162 (m), 172 (m), 187 (m), 310 (s), 369 (w), 500 (m),
33 (w).
O : 54 (vw), 77 (w), 88 (w), 101 (m), 113
2 3
(
6
EXPERIMENTAL DATA
■
[Sr(ddbfoH) ](ddbfo) ·ddbfoH (3). A Schlenk flask fitted with a
4 2
All reactions and manipulations were conducted under an atmosphere of
reflux condenser equipped with a N inlet/oil bubbler was charged with
2
dry N using a standard Schlenk setup. The starting materials, barium
metal Sr (3.02 g; 34.47 mmol), toluene (40 mL), and 2,3-dihydro-2,2-
dimethyl-7-benzofuranol (ddbfoH, 42.47 g; 258.53 mmol), and the
resulting mixture was stirred at room temperature until all of the metal
had been consumed (usually 3−4 h). The mixture was then filtered to
give a clear, dark green solution, which was reduced in volume to
approximately 25 mL. Hexanes (15 mL) were then added to the mixture,
providing colorless blocks of 3 following a hold period of 72 h (30.90 g;
2
(
pieces, 99%), strontium (granular, 99%), AlMe (2.0 M in toluene),
3
ddbfoH (2,3-dihydro-2,2-dimethylbenzofuran-7-ol; 99%), and
europium(III) oxide (Eu O3 powder 99.9%), were obtained from
2
Aldrich, Germany, and used as received. InMe (2.13 M in toluene) was
3
obtained from the Department of Chemistry at the Warsaw University
of Technology. Toluene and hexanes were distilled from Na/
benzophenone and P O , respectively. Infrared spectra were recorded
25.02 mmol; 73%). Anal. Calcd for 3, C H O Sr (1235.00): C, 68.07;
2
5
70 82 14
−1
on a Bruker 66/s FT-IR spectrophotometer in Nujol mulls.
H, 6.71; Sr, 7.09. Found: C, 68.32; H, 6.43; Sr, 7.63. FT-IR (cm , Nujol
Thermogravimetric-differential thermal analyses (TGA-DTA) were
mull): 3410 (m), 1628 (m), 1592 (m), 1460 (s), 1376 (s), 1304 (s),
recorded in a N and air atmosphere on a Setaram SETSYS 16/18. NMR
1136 (s), 1066 (m), 1020 (s), 878 (s), 792 (s), 722 (s), 590 (m), 522
2
1
spectra were obtained on Bruker 300 MHz AMX and 500 MHz (Avance
(m), 440 (m), 430 (m), 412 (m), 352 (m). H NMR (CDCl , 298 K): δ
3
5
00) spectrometers. GC-MS analyses were recorded on a gas
10.71 (br s, OH), 7.40−6.59 (m, 3H of Ph), 2.72 (s, CH ), 1.29 (s,
2
13
chromatograph with an HP 5971A mass detector and an HP 5965B
2CH ). C NMR (CDCl , 298 K): δ 148.3 (s, (C(O
))C(O)),
3
3
phenoxo
infrared detector (Hewlett-Packard). Microanalyses were conducted
143.7 (s, C(Ophenoxo), 128.2 (s, C(H)C(CH )), 122.4 (s, (CH)
2
9
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Inorganic Chemistry
Article
Scheme 1. Synthesis of 1, 2, 4, and 5
CH(CH)), 116.9 (s, (CH)CH(C)), 116.2 (s, C(Ophenoxo)CH(CH)),
atmospheric conditions to allow for a comparison of their luminescence
properties.
8
7.7 (s, C(CH ) ), 44.0 (s, CH ), 28.1 (s, 2CH ).
3 2 2 3
[
Sr{(μ-ddbfo) AlMe } ] (4) and [Me Al(μ-ddbfo)] (5). A Schlenk
Details of X-ray Data Collection and Reduction. X-ray
diffraction data were collected using a KUMA KM4 CCD (ω scan
technique) diffractometer equipped with an Oxford Cryosystem-
Cryostream cooler. The space groups were determined from systematic
absences and subsequent least-squares refinement. One frame checked
every 50 frames showed no crystal decay. Lorentz and polarization
corrections were applied. The structures were solved by direct methods
2
2 2
2
2
flask was charged with 3 (0.93 g; 0.75 mmol) and toluene (15 mL), and
the resulting clear, yellow-green solution was stirred vigorously and
cooled to 0 °C. A 2.0 M solution of AlMe in toluene (1.9 mL; 3.80
3
mmol) was then added to the mixture in a dropwise manner. The
solution was warmed to room temperature, toluene (30 mL) was added,
and the resulting mixture was stirred at room temperature for 24 h. The
solution was then filtered, and the filtrates were reduced in volume to
approximately 30 mL. Hexanes (10 mL) were then added, and the
resulting mixture was cooled to −5 °C. Following a hold period of 72 h,
two kinds of colorless crystals formed from within the biphasic solution,
namely, blocks of 4 and needles of 5. The significant differences in size
and crystal morphology allowed us to isolate the two types. The crystals
2
and refined by full-matrix-least-squares on F using the SHELXTL
3
7
package. Non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atom positions were calculated and added to the
structure factor calculations, but were not refined. Scattering factors and
38
Δf′ and Δf′′ values were taken from the literature.
With the exception of structure factors, all of the data have been
deposited with the Cambridge Crystallographic Data Centre (CCDC)
in association with earlier communications (barium aryloxide) or as
were separated under a N atmosphere using a Pasteur pipet. Anal. Calcd
for 4, C H O SrAl (854.50): C, 61.85; H, 6.61; Sr, 10.25; Al, 6.32.
Found: C, 60.99; H, 6.93; Sr, 10.01; Al, 6.02. Anal. Calcd for 5,
2
31
44
56
8
2
supplementary publications CCDC 878064, 878065, and 878063 for 1,
C H O Al (440.50): C, 65.44; H, 7.78; Al, 12.25. Found: C, 64.98; H,
2
4
34
4
2
2
, and 3. Copies of the data can be obtained free of charge by application
−1
7
1
(
(
(
.67; Al, 12.07. FT-IR of 4 (cm , Nujol mull): 1891 (vw), 1808 (vw),
618 (vs), 1590 (m), 1488 (vs), 1472 (vs), 1362 (s), 1307 (vs), 1290
s), 1234 (m), 1190 (s), 1155 (m), 1130 (s), 1111 (s), 1060 (m), 1040
vs), 969 (w), 900 (w), 867 (s), 843 (m), 771 (vs), 717 (s), 670 (s), 587
m), 529 (w), 500 (w), 479 (m), 373 (w). FT-IR of 5 (cm , Nujol
mull): 1889 (vw), 1812 (vw), 1617 (vs), 1590 (m), 1488 (vs), 1460 (vs),
370 (s), 1311 (vs), 1293 (s), 1239 (m), 1190 (s), 1161 (m), 1131 (s),
110 (s), 1055 (m), 1033 (vs), 971 (w), 903 (w), 871 (s), 842 (m), 770
vs), 716 (s), 670 (s), 586 (m), 524 (w). H NMR of 4 (C D CD , 298
to CCDC, 12 Union Road, Cambridge CB21EZ, UK (e-mail: deposit@
ccdc.cam.ac.uk).
−1
RESULTS AND DISCUSSION
■
Synthesis of Compounds 1−5. To the best of our
1
1
(
26
knowledge, there is a complete lack of barium−indium and
1
strontium−aluminum species containing a M−O
−M′ (M =
alkoxo
6
5
3
2
+
2+
3+
3+
K): δ 7.05−6.56 (m, 3H of Ph), 2.50 (s, CH ), 1.12 (s, 2CH ), −0.18 (s,
Ba , Sr ; M′ = In , Al ) motif. Therefore, as an initial point of
2
3
1
2
Al−CH ). H NMR of 5 (C D CD , 298 K): δ 7.10−6.56 (m, 3H of
our project, we prepared the mononuclear barium 7-benzofuran-
3
6
5
3
Ph), 2.56 (s, CH ), 1.22 (s, 2CH ), −0.17 (s, 2Al−CH ). Purity of
2
3
3
oxide. The reaction of barium aryloxide [Ba(ddbfoH) ]-
4
SrAl O (%): C, 0.04; H, 0.00. EDS: Sr/Al = 0.5 (±0.01). Purity of Al O
3
36
2
4
2
(
ddbfo) ·ddbfoH (ddbfoH = 2,3-dihydro-2,2-dimethyl-7-
−1
2
(
(
4
%): C, 0.00; H, 0.00. Raman (cm ) of SrAl O : 50 (w), 90 (m), 107
2
4
benzofuranol) with InMe in toluene (Scheme 1) led to the
3
s), 114 (s), 129 (vs), 137 (m), 146 (m), 171 (m), 178 (m), 190 (w),
67 (s), 500 (w), 787 (w). Raman (cm ) of Al O : 58 (w), 78 (m), 90
m), 103 (m), 117 (m), 128 (vs), 382 (w), 420 (m).
Oxide Preparation. In a typical procedure, the precursor was heated
at the desired temperature for 5 h in air. Following decomposition, the
oxide products were identified by PXRD. The morphologies and
elemental compositions of BaIn O , In O , SrAl O , and Al O particles
were investigated using scanning and transmission electron microscopy
equipped with an energy-dispersive spectrometer (SEM-EDS and TEM-
EDS). Carbon and hydrogen contaminations following thermolysis
were examined by elemental analysis. Phase purity was also confirmed
by Raman spectroscopy (see Supporting Information).
Preparation of Eu-Doped Oxides. Eu-doped samples were
synthesized by mixing oxides derived from 2 and 4 with Eu O , with
the mixture being ground in an alumina mortar with acetone as a wetting
medium. The resulting raw powder of In O :Eu was sintered in air at
000 °C. The Eu concentration was 3 mol % with respect to In. The raw
powder of Sr0.99Eu0.01Al O was sintered at 1300 °C under oxidizing
air) and reducing (mixture N −H 25%) atmospheres. SrAl O :Eu
powders were also obtained using a traditional ceramic method.
Stoichiometric amounts of SrCO , Al O , and Eu O were ground with
−1
abstraction of the hydroxyl protons from the cation sphere of
barium and the subsequent evolution of methane MeH, as
2
3
(
confirmed by GC/MS analysis. Consequently, the organo-
+
metallic cation InMe could readily coordinate to the barium
2
anion [Ba(ddbfo)4]2 core to form a heterobimetallic [Ba{(μ-
−
2
4
2
3
2
4
2
3
ddbfo) InMe } ] (1) aryloxo-organometallic complex. Mean-
2
2 2
while, the InMe was also reacted with ddbfoH to form dimeric
3
complex [Me In(μ-ddbfo)] (2). Subsequent workup gave two
2
2
kinds of colorless crystals, namely, blocks and needles of 1 and 2,
respectively, which were separated prior to any further analysis
under a N atmosphere using a Pasteur pipet. Such an easily
2
2
3
performed isolation method was possible due to significant
differences in size and crystal morphology. Needle-like crystals
grew on the Schlenk walls, and blocks were much smaller and
localized on the bottom of the flask. Unfortunately, up to now we
have not been able to obtain 1 and 2 separately in the pure
crystalline form.
3+
2
3
1
2
4
(
2
2
2
4
The crystal structures of 1 and 2 were determined according to
3
2
3
2
3
acetone and sintered at the same temperature under the same
the parameters presented in Table 1 and are described in the
9
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Inorganic Chemistry
Article
Experimental Section. Selected bond lengths and angles are
outlined in Tables 2 and 3.
109.65(8)° and 107.49(8)°, whereas they are 109.67(7)° and
31
1
11.47(7)° for [Ba{(μ-ddbfo) GaMe } ].
2 2 2
The molecular structure of 2 is shown in Figure 2. Complex 2
is composed of two five-coordinate indium atoms, with each of
Table 1. Crystallographic Data for 1−3
the metal centers being surrounded by three oxygen atoms from
−
1
2
3
the ddbfo ligands and two carbon atoms from the methyl group.
chemical formula
fw
5(C H BaIn O )
C H In O
C H O Sr
The indium atoms are bridged by the two aryloxo oxygens of the
4
4
56
2
8
24 34
2
4
70 82 14
5399.34
100(2)
C2/c
616.15
1234.98
100(2)
In O unit, where the In−O bond distance is 2.193(2) Å. The
2
2
temp (K)
space group
a [Å]
100(2)
coordination sphere of the metal centers possesses highly
distorted trigonal-bipyramid geometry. Each of the In atoms lay
in an equatorial plane constituted by one bridging aryloxo oxygen
atom from a benzofuranoxide ligand and two carbon atoms from
the methyl groups. The axial positions are occupied by an ether
C2/c
P2 /c
1
40.809(8)
12.708(4)
42.708(9)
90.00
17.075(4)
9.496(3)
17.503(4)
90.00
20.157(5)
14.714(4)
21.812(5)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
Z
oxygen atom and a second aryloxo oxygen. The In−O(
bond
ether)
91.08(4)
90.00
117.41(4)
90.00
98.99(3)
90
distance is 2.641(2) Å and is much longer than the
corresponding value observed in In−O(alkoxo). Many different
suggestions have appeared in the literature regarding the nature
22144(9)
4
2519.4(15)
4
6390(3)
4
of this bonding interaction, and an interesting analysis of this
3
47
ρ [g/cm ]
1.620
1.624
1.299
́
issue has been reported by Lewinski and Zachara. On the basis
μ(Mo K ) [mm−1]
48−51
15.48
1.86
0.91
α
of their studies, and by analogy with other group 13 metals,
R1 (>2σ)
0.042
0.0202
0.0456
0.039
this type of bond has been defined as a secondary or noncovalent
interaction. Spectroscopic and analytical data for 1 and 2
confirmed their structural composition (see Experimental
Section).
wR2 (>2σ)
0.107
0.066
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 1
Since strontium is a technologically important ion in double
oxide materials, such as spinels and perovskites, in the next
stage of the current studies we prepared mononuclear strontium
Ba(1)−O(10)
Ba(1)−O(11)
Ba(1)−O(20)
Ba(1)−O(21)
In(1)−O(11)
In(1)−O(21)
In(1)−C(1)
In(1)−C(2)
Ba(1)−O(11)−In(1)
Ba(1)−O(21)−In(1)
2.868(5)
2.724(4)
2.858(5)
2.733(4)
2.146(4)
2.155(4)
2.152(7)
2.171(7)
112.10(18)
111.46(18)
5
2
benzofuranoxide [Sr(ddbfoH) ](ddbfo) ·ddbfoH (3) (ddbfoH
4
2
=
2,3-dihydro-2,2-dimethylbenzofuran-7-ol). Complex 3 is air-
sensitive, but could be stored for extended periods under dry N2.
This complex was obtained according to the direct reaction of
metallic strontium with an excess of ddbfoH in toluene (Scheme
).
Crystallization of 3 from a mixture of toluene and hexanes
provided colorless crystals. The molecular structure of 3 (Figure
) was determined as outlined in the Experimental Section and
Table 1.
Complex 3 exists as an ionic compound with two anionic
2
3
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2
In(1)−O(10)
In(1)−O(11)
In(1)−C(1)
In(1)−C(2)
O(10)−In(1)−O(11)
O(10)−In(1)−C(1)
O(10)−In(1)−C(2)
O(11)−In(1)−C(1)
O(11)−In(1)−C(2)
2.641(2)
2.195(2)
2.139(2)
2.143(2)
69.88(6)
86.73(8)
93.75(8)
108.66(8)
104.89(7)
ddbfo− ligands and a neutral 7-benzofuranol outside the
coordination sphere of the strontium cation. The cation and
the anions are connected by hydrogen bonds, which reveal, on
closer inspection, that the ddbfoH molecules have remained
within the coordination sphere of strontium in the solid state. All
hydrogen atoms of OH groups were clearly located from
difference Fourier maps and refined without restraints. Close
analysis of the O−H and O···H distances (Table 4) shows that all
ligands from the metal coordination sphere keep their hydroxy
hydrogens. The distances O(11)−H(11), 0.82(2); O(31)−
H(31), 0.93(2); O(41)−H(41), 0.90(2); O(21)−H(61),
1.05(2); and O(71)−H(71), 0.95(2) clearly indicate the
existence of O−H bonds. On the other hand, the distances
O(61)···H(11), 1.78(2); O(51)···H(31), 1.55(2);
O(51)···H(41), 1.58(2); O(61)···H(61), 1.41(2); and
O(61)···H(71), 1.90(2) confirm that there are only intermo-
lecular contacts. The hydrogen bonds were also found to have
persisted in solution, with their presence being confirmed by the
Figure 1 presents a view of the molecular structure of 1. The
barium cation is surrounded by eight oxygen atoms from the four
benzofuranoxide ligands and possesses dodecahedral geometry.
The indium atoms are four-coordinate, with each of the atoms
being occupied by two donor aryloxo oxygens and two carbon
atoms from the methyl groups. The coordination sphere of the
indium cations possesses a slightly distorted tetrahedral
geometry. The Ba−O bond distances range from 2.724(4) to
1
2
.868(5) Å, which is comparable with those observed for [Ba{(μ-
appearance of a broad singlet located at 10.71 ppm in the H
3
+
3+ 31
ddbfo) M′Me } ] (M′ = Al , Ga ) and other barium/group
NMR spectrum. The Sr−O
bond distances range from
2
2
2
(aryloxo)
3
2,39−46
1
3 heterobimetallic complexes reported in the literature.
2.549(3) to 2.611(3) Å and are much longer than those reported
53
The In−O distances in 1 are 2.146(4)−2.155(4) Å, and the In−
C distances are 2.152(7) and 2.171(7) Å. The Ba−O−In bond
angles range from 111.46(18)° to 112.10(18)°. For comparison,
the Ba−O−M′ bond angles for [Ba{(μ-ddbfo) AlMe } ] are
for [Sr(OPh) (PhOH) (THF) ],
[{Sr (OMes) (μ-
2 2
54
8
2
6
2
1
OMes) (η -en)(η -en)(H O)}(μ-en)]·3en (MesOH = 2,4,6-
trimethylphenol; en = ethylenediamine), and
[Sr (OMes) (dme) ] (dme = 1,2-dimethoxyethane), whereas
2
2
55
2
2
2
2
4
4
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Figure 1. Molecular structure of 1 (H atoms have been omitted for clarity).
the Sr−O
bond distances are longer than Sr−O
and
(
ether)
(aryloxo)
range from 2.648(3) to 2.733(3) Å. The molecular structure of 3
is strongly supported by the spectroscopic data and is also similar
to the structure proposed for its corresponding barium
36
derivative. It is worthy of note that, to the best of our
knowledge, there are only a few examples of group 2 homoleptic
alkoxide complexes in the literature. The largest group was found
3
5,41,42,55−66
for barium compounds,
including heterometallic,
molecular, and ionic complexes. A few examples have also been
67−72
73−78
indentified for magnesium,
species.
calcium,
and strontium
7
8−85
Complex 3 was employed in a reaction with AlMe (Scheme
3
1
), leading to methane evolution and the linking together of
−
+
ddbfo ligands with the appropriate AlMe moiety to form both
2
[
Sr{(μ-ddbfo) AlMe } ] (4) and [Me Al(μ-ddbfo)] (5). The
2 2 2 2 2
block- and needle-like crystals were separated according to the
analogous procedure described for the mixture of 1 and 2.
Unfortunately, their crystallographic structures could not be
determined completely because of the low quality of crystals
obtained. In spite of this, their structures were clearly identifiable
because of the resemblance to complexes 1 and 2. These
similarities were also strongly supported by the spectroscopic
and elemental analysis data. For example, the signals of the
aromatic protons were similar to those found for ddbfoH.
Furthermore, the signals corresponding to the AlMe2+ moieties
were observed at −0.18 for 4 and at −0.17 ppm for 5. The results
Figure 2. Molecular structure of 2 (H atoms have been omitted for
clarity).
Scheme 2. Synthesis of 3
1
obtained from H NMR analysis were also confirmed by FT-IR
spectroscopy. For complex 4, the bands at 500, 479, and 373
−1
cm were assigned to the ν(Sr−O) vibrational modes, and peaks
−1
at 587 and 529 cm were characteristic of ν(Al−O) stretching
vibrations. Furthermore, the ν(Al−O) bands of 5 were observed
−1
at 586 and 524 cm . Based on spectroscopic studies, elemental
31
analysis, and our previous investigative experience, the final
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Figure 3. Molecular structure of 3 (with the exception of the hydroxyl hydrogen, the H atoms have been omitted for clarity).
Table 4. Hydrogen Bond Parameters of 3
microanalysis, powder X-ray diffraction, microscopy (SEM-EDS
and TEM-EDS), physisorption analyses, and Raman spectros-
copy.
D−H···A
D−H
H···A
D···A
∠D−H···A
O(11)−H(11)···O(61)
O(31)−H(31)···O(51)
O(41)−H(41)···O(51)
O(21)−H(61)···O(61)
O(71)−H(71)···O(61)
0.82(2)
0.93(2)
0.90(2)
1.05(2)
0.95(2)
1.78(2)
1.55(2)
1.58(2)
1.41(2)
1.90(2)
2.576(2)
2.462(2)
2.472(2)
2.447(2)
2.809(2)
163(2)
167(2)
167(2)
165(2)
158(2)
The diffraction patterns of the resulting metal oxides (Figure
4
a−d) remained in agreement with those of the barium/indium
BaIn O and strontium/aluminum SrAl O spinels and indium
2
4
2
4
In O and aluminum Al O oxides reported in the inorganic
2
3
2
3
87
crystal structure database (ICSD). Furthermore, no residual
2
+
peaks corresponding to group 2 carbonates MCO (M = Ba ,
3
compositions of complexes 4 and 5 are proposed to be [Sr{(μ-
ddbfo) AlMe } ] and [Me Al(μ-ddbfo)] , respectively.
2+
Sr ) were observed at lower 2θ values (2θ < 10°) for complexes
2
2
2
2
2
1
and 4. The presence of carbonates was also excluded by
Preparation of Oxide Materials and Their Properties.
The complexes 1, 2, 4, and 5 appeared to be natural molecular
precursors for both spinel-like materials and group 13 oxides with
elemental analysis and Fourier transform infrared spectroscopy.
The phase purity of the resulting powders was confirmed using
Raman spectroscopy (see Supporting Information).
2
+
2+
3+
3+
compositions of type MM′ O (M = Ba , Sr ; M′ = In , Al )
2
4
Using the Debye−Scherrer equation, the average grain sizes
were inter alia calculated from the PXRD spectra for the half-
width of the three most intense peaks (designated on the basis of
the line extending with appropriate diffractive 2θ angles: 30.7°,
3
+
3+
and M′ O (M′ = In , Al ), respectively. These compounds
2
3
underwent thermal decomposition in air at the temperatures
specified in Table 5. It is worthy of note that the thermal
3
1.7°, and 44.3° for BaIn O ; 30.6°, 35.6°, and 51.5° for In O ;
2 4 2 3
Table 5. Thermolysis Conditions and Purity of the Resulting
Oxides
2
8.5°, 29.3°, and 35.2° for SrAl O ; and 35.3°, 43.5°, and 57.6°
2 4
for Al O (Table 6).
2
3
The morphology and composition of the targeted oxide
powders were studied by SEM-EDS/TEM-EDS. The morphol-
ogies of the desired powders are presented in Figures 5 (SEM)
and 6 (TEM).
precursor
temperature (°C)
product
BaIn O
color
1
2
4
5
1400
850
light brown
light orange
white
2
4
In O
2
3
1200
900
SrAl O
2
4
Results of the EDS analyses were consistent with the phase
identification by PXRD, where spinels or group 13 oxides
appeared to be the only compounds present in the samples.
Standardless EDS analysis was performed for many of the grains
(see Supporting Information for EDS spectra of the oxide
powders examined) and confirmed the proper M:M′ ratios (Ba/
In and Sr/Al = 0.5 ± 0.01). With the exception of barium,
strontium, indium, aluminum, and oxygen, no other elements
were detected in the samples. Only residual carbon content, from
the high-purity conducting carbon tabs used to fix the powder
materials, was detected during the SEM-EDS analysis. The
analysis revealed irregular morphologies in the resulting metal
oxides; although in the case of 2, which was decomposed at 850
Al O
white
2
3
decomposition of metal alkoxides containing bulky chelating
ligands was much more complex. Furthermore, in comparison
with metal alkoxides containing small monodentate RO groups
R = Me, Et, Pr), the thermolysis process was much slower and
occurred over an extended time period. This extended time
period was necessary to fully decompose and remove organic
contaminants from the metal oxide network. Complexes 1, 2, 4,
and 5 were thermolyzed for 5 h, on the basis of the phase
diagrams of BaIn O , SrAl O , In O , and Al O , to give phase-
pure powders. The resulting materials were analyzed using
3
1
−
i
(
86
2
4
2
4
2
3
2
3
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Figure 4. PXRD pattern of (a) BaIn O derived from 1, (b) In O derived from 2, (c) SrAl O derived from 4, and (d) Al O derived from 5.
2
4
2
3
2
4
2
3
Table 6. Dinitrogen Physisorption Data and Particle Size
a
Predictions
particle size diameter
[nm]
S
S
δ
3
BET
[m /g]
Langmuir
[m /g]
2
2
oxide
[g/cm ]
N2
PXRD
8
8
9
9
8
9
0
1
BaIn O4
0.685
20.62
2.05
1.12
31.30
3.44
6.96
7.12
3.49
3.89
1258
41
1245−1262
38−42
820−845
310−325
2
In O3
2
SrAl O4
839
316
2
Al O3
2
4.88
9.04
a
Based on the dinitrogen physisorption and PXRD data.
°C, regular diamond-shaped crystals of indium oxide were
obtained (Figure 6). We are convinced that the use of other
methods such as sol−gel or hydrothermal would allow for the
construction of material with a certain shape and grain size. The
primary aim of the current studies was to check the suitability of
these molecular precursors for application in a so-called single-
source strategy for obtaining highly phase-pure oxide materials
with a strictly defined specific composition.
Figure 5. SEM images of (a) BaIn O , (b) In O , (c) SrAl O , and (d)
2
4
2
3
2
4
Al O .
2
3
The results obtained from PXRD and SEM-EDS/TEM-EDS
were further supported by Raman analysis of resulting metal
oxide particles. The spectra (see Supporting Information)
exhibited well-defined bands for BaIn O , SrAl O , In O , and
Al O materials in complexes 1, 4, 2, and 5, respectively. There
were no traces of organic materials and no bands characteristic of
the C−O vibrations of barium or strontium carbonate.
2
3
2
4
2
4
2
3
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The reduced adsorption isotherm for indium oxide deviated
from the other curves in the low-pressure ranges, which
suggested the presence of micropores. This was confirmed by
the presence of a clear and significant hysteresis loop in the
adsorption−desorption isotherm. Additional physisorption tests
were therefore carried out at relative pressures in the 10− < p/p°
7
<
0.01 range, to examine the pore size distribution. The resulting
curve corresponded well with the Langmuir model. The analysis
of the micropore size distribution was based on the Horvath−
94
Kawazoe model. The pore size distribution presents a single
maximum (Figure 8). Micropores were present in a wide range of
Figure 6. (a) TEM images and (b) SAED diffraction of the In O heated
2
3
at 850 °C.
Moreover, no ν(O−H) stretching bands corresponding to
hydroxide aluminum or indium compounds were observed.
The nitrogen physisorption characteristics of the resulting
metal oxides were examined, and the specific surface areas and
total pore and micropore volumes were determined from the
resulting isotherms (Figure 7a,b) (Table 6). Surface areas were
measured using the Langmuir and Brunauer−Emmett−Teller
Figure 8. Micropore size distribution of In O particles.
2
3
sizes from 1.2 to 1.8 nm, with a maximum occurring at a pore
width of 1.45 nm. This suggests that the In O nanoparticles
2
3
(
BET) models for relative pressures within 0.05 < p/p° < 0.30.
The compliance of the isotherms of SrAl O , Al O , and BaIn O
4
possessed an unsettled surface because of the presence of
micropores.
2
4
2
3
2
9
2,93
with a model isotherm of α-Al O published by Cejke et al.
Luminescent Properties of a Eu-Doped SrAl O Spinel
2
3
2
4
showed that the resulting metal oxides were typical for materials
lacking micro- and mesopores. The volume of a specific surface
area was almost exclusively associated with the development of
the surface as a result of the fragmentation of material on the
micro- and nanoparticles.
and In O . Eu-doped alkaline earth aluminates have been widely
2 3
studied in recent years due to their good luminescent properties
95−98
such as high brightness, longevity, and chemical stability.
These phosphors have been used in a variety of applications, with
99,100
examples including display devices and the lamp industry.
Figure 7. Adsorption isotherms of (a) SrAl O (solid circles), Al O (solid diamonds), BaIn O (solid triangles), and (b) In O .
2
4
2
3
2
4
2
3
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2
+
6
1
7
2+
Eu -activated strontium aluminate has been considered for use
corresponding to a 4f 5d −4f energy level transition of Eu .
101
as a green phosphor in white light-emitting diodes (LEDs),
whereas SrAl O :Eu has been investigated for use as a red
phosphor for LEDs.
The PXRD patterns of Sr0.99Eu0.01Al O derived from complex
and prepared using the solid-state method from a SrCO and
The band ranging from 230 to 270 nm was attributed to the
charge transfer band (CTB) of the Eu −O bond.
energy position of this charge transfer band was closely related to
3
+
2+
2−
100
The
2
4
99
2
+
2+
the coordination number of Eu and the covalency of the Eu −
2
4
2−
4
O bond. Another band in the UV region (peak at 198 nm) was
101
3
Al O mixture are shown in Figure 9 (time of thermolysis, 10 h).
2
assigned to matrix absorption. The absorption spectrum of the
sample heated in an air atmosphere showed bands ranging from
3
1
90 to 225 nm and 230 to 300 nm, which were attributed to
3+
2−
matrix absorption and an Eu −O charge transfer transition,
3
+
respectively. The typical 4f−4f transitions of Eu were not
observed, although a broad band was observed in the range of
3
50 to 550 nm.
2+
The photoluminescence spectra of SrAl O :Eu derived from
2
4
4
are presented in Figure 11. The emission spectrum (Figure
1
1b) was observed as a strong green emission band, which
6
1
7
peaked at 520 nm and was assigned to the typical 4f 5d −4f
2+
transition of Eu . It is clear that the intensity of emission upon
excitation at λexc = 350 nm (Eu2+ 4f−5d transition) was much
higher than that observed upon excitation at λ = 240 nm
exc
2+
2−
(
Eu −O CTB), as shown in the inset of Figure 11. The
excitation spectrum (Figure 11a) corresponding to the peak at
20 nm showed an asymmetrical band (peak at 360 nm), which
5
7
was attributed to the transitions from the 4f ground state to the
excited state 4f 5d . The asymmetry of both emission and
6
1
excitation bands might be considered to be the result of different
Figure 9. PXRD pattern of Sr0.99Eu0.01Al O (a) derived from complex
2
4
2
+
4
, (b) prepared using the ceramic method, and (c) SrAl O ICSD 26466.
Eu distributions in the SrAl O4 structure. No peaks
2
2
4
3+
corresponding to the f−f transitions of Eu appeared in the
3+
spectra, which confirmed that the Eu ion has been effectively
The similar ionic radii of Eu2+ (0.130 nm) and Sr2+ (0.127 nm)
2+
reduced to Eu in the matrix.
and the small amount of doped ion exerted no significant
Figure 12 shows the photoluminescence spectra of SrA-
100
3+
influence on the structure of the host. In both cases, the
diffraction peaks of SrAl O were in good agreement with the
l O :Eu , which had been derived from 4 by sintering in air. The
2 4
2
4
excitation spectrum of the emission at λem = 613 nm (Figure 12a)
standard ICSD database (ICSD 26466).
Figure 10 shows the diffuse reflectance spectra of two different
contained a series of narrow peaks in the region from 350 to 550
3
+
nm, which resulted from 4f−4f transition within the Eu ions
5
5
SrAl O :Eu samples prepared by heating within two different
2
4
and originated from absorptions to the D (361 nm), L (380
4 7
5
5
5
5
atmospheres, namely, air and a N /H mixture, across the
2
2
nm), L (391 nm), D (412.5 nm), D (462 nm), and D (530
6 3 2 1
98
spectral region from 190 to 850 nm at room temperature. The
nm) states. The broad band in the range from 245 to 335 nm
3
+
absorption spectrum of the sample sintered in a reducing (N and
2
corresponded to a charge transfer transition caused by a Eu −
O interaction. A further band, ranging from 200 to 240 nm, was
2−
H ) atmosphere exhibited a broad band (peak at 350 nm)
2
observed and attributed to the host lattice absorption. The
emission spectrum (Figure 12b) consisted of characteristic sharp
lines, peaking at 578, 590, 613, 647, and 682 nm and attributed to
5
7
7
7
7
7
the transitions from D to the F , F , F , F , and F levels,
0
0
1
2
3
4
respectively. The most intense line was a red emission attributed
5
7
to a D − F electric dipole transition accompanied by the
0
2
5
7
presence of a forbidden D − F transition, which indicated that
0
0
3
+
the local environment of the Eu ions was not centrosymmetric.
Furthermore, the high number of lines present in the spectrum
suggested more than one site existed for the europium ions in the
SrAl O matrix. The oxidation number of the europium ions and,
2
4
consequently, the photoluminescence properties of Eu-doped
SrAl O depended strictly on the heating atmosphere, as can be
2
4
seen from the spectra (Figures 11 and 12). Sintering in air gave
samples containing trivalent europium with emission in the red
wavelength region, whereas sintering in a N /H mixture
2
2
provided the europium dopant as a divalent ion with emission
in the green wavelength region.
The emission spectra of Sr0.99Eu0.01Al O4 synthesized
2
according to a conventional method were collected. Figure 13
shows the curves recorded and compared with the spectra of
specimens derived from 4. The emission spectra of the samples
obtained according to different methods appeared similar,
Figure 10. Absorption spectra of Sr0.99Eu0.01Al O heated in (a) a
mixture of nitrogen and hydrogen and (b) air atmosphere.
2
4
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2+
Figure 11. Photoluminescence spectra of SrAl O :Eu derived from 4: (a) excitation spectrum (λem = 520 nm) and (b) emission spectrum (λexc = 350
2
4
nm). The inset shows emission upon excitation at 240 nm (dashed line) and 350 nm (solid line).
3+
Figure 12. Photoluminescence spectra of SrAl O :Eu derived from 4: (a) excitation spectrum (λem = 613 nm) and (b) emission spectrum (λ = 290
2
4
ex
nm).
although the intensity of samples derived from the molecular
precursor exhibited a higher intensity. This phenomenon has also
been observed for strontium aluminate doped with both divalent
and trivalent europium ions.
In turn, the diffuse reflectance spectra (Figure 14) of pure and
Eu3+ ion, respectively (Figure 15b). The excitation spectrum
(Figure 15a) was obtained by monitoring the most intensive
7
5
emission of electric dipole transition F
− D
. It exhibited peaks
0
2
102
7
5
located at 465 and 532 nm that were assigned to the F − D and
0
2
7
5
104
F − D transitions, respectively. The absence of an indium
0
1
Eu-doped In O derived from 2 were characterized by similar
oxide host band confirmed that there was no energy transfer
2
3
between the matrix and Eu3+ ion.
curves. The broad absorption band was assigned to the wide band
103
gap (3.55−3.75 eV) of indium oxide. Lines corresponding to
3
+
the 4f−4f transitions of Eu were not observed.
CONCLUSIONS
■
3
+
Photoluminescence spectra for In O :Eu are shown in
2
3
In conclusion, we have developed a simple synthetic approach to
well-defined and previously unreported Ba−In and Sr−Al
heterometallic aryloxo-organometallic complexes derived from
barium or strontium 7-benzofuranoxide and trimethyl In and Al
species. The corresponding indium and aluminum dimers were
also isolated as byproducts from these reactions. The
predesigned nature of these structures, on a molecular level,
made them perfect candidates for both spinel-like and group 13
oxide nanoparticles/particles. Furthermore, these materials were
Figure 15. Emission peaks resulting from the transitions of the
3+
Eu ion were not observed upon excitation at λexc = 350 nm
band gap of In O , inset in Figure 15), indicating that there was
(
2
3
no efficient energy transfer from the host to the activator ion.
7
5
Only direct excitation from the ground state F to D of the
0
2
3+
Eu ion provided a series of emission peaks centered at 579.4,
85, 610.6, 649, 708, and 764 nm that contributed to the
transitions from the D to F (J = 0, 1, 2, 3, 4, 5) levels of the
5
5
7
0
J
9
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Inorganic Chemistry
Article
from an economic perspective compared to the corresponding
conventional solid-state reactions using barium and strontium
carbonates and an appropriate group 13 oxide, which typically
require extended reaction times and high temperatures.
Preliminary investigations on the Eu-doped SrAl O and In O
3
2
4
2
phosphors have shown that the oxides obtained could be
considered as matrices for lanthanide ions. The dependence of
the luminescence properties of the Eu-doped strontium
aluminates on the atmosphere employed during sintering has
been investigated. An oxidizing atmosphere was shown to
provide materials that emitted in the red wavelength region,
whereas a reducing atmosphere afforded samples with green
emission. Both phosphors were suitable candidates for
applications in LED devices. Phosphors derived from the
molecular precursor exhibited higher emission intensity than
3
+
those obtained using the solid-state reaction. In O :Eu showed
2
3
an emission corresponding to a 4f−4f transition only after direct
7
5
3+
excitation ( F - D ) of the Eu ions. There was no energy
0
2
Figure 13. Comparison of the emission spectra of Sr0.99Eu0.01Al O4
3+
2
transfer between the matrix and the Eu ions. Further studies of
the luminescent properties of the obtained oxide networks are
currently under way in our laboratories.
obtained from the molecular precursor (solid line) and the ceramic
method (dashed line) sintered in (a) air and (b) N /H mixture upon
2
2
excitation at λ = 290 nm and λ = 350 nm, respectively.
ex
ex
ASSOCIATED CONTENT
■
*
S
Supporting Information
Full crystallographic data, Raman spectra, EDS spectra. This
material is available free of charge via the Internet at http://pubs.
acs.org.
AUTHOR INFORMATION
■
Corresponding Author
E-mail: piotr.sobota@chem.uni.wroc.pl. Tel: +48 071 375 73
*
0
6.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Figure 14. Absorption spectra of (a) pure and (b) Eu-doped In O .
■
2
3
The authors would like to express their gratitude to the National
Science Centre (grant numbers: 2011/03/B/ST5/01040 and
2
011/01/N/ST5/02408) for financial support. We would also
like to thank Dr. Wojciech Bury and Prof. Janusz Lewinski from
the Department of Chemistry at the Warsaw Technical
́
University, for their assistance with the N sorption measure-
2
ments.
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