Synthesis of Er-complexes for photonic applications

Article abstract of DOI:10.1016/j.jpcs.2007.01.003

We present a new approach of introducing erbium ions onto thin surface layers of silica glass substrates based on soaking of solution of erbium complexes. Different types of Er³⁺ complexes with 2,2′-dipyridyle, 1,10-phenantroline, 8-hydroxyquinoline and ethylendiamine ligands and nitrate, thiocyanate and acetate anions were prepared. Composition of the complexes was determined by elementary analysis and by FT-IR spectroscopy. Decomposition temperature was measured by thermogravimetric analysis. Erbium doped surface layers exhibit strong photoluminescence with maximum on 1533 nm and full width at half maximum above 50 nm.

Full text of DOI:10.1016/j.jpcs.2007.01.003

ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 68 (2007) 1272–1275
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Synthesis of Er-complexes for photonic applications
Ã
ˇ
Zdenek Sofer , Pavlına Tresnakova, Jarmila Spirkova, Stanislav Rubas, Martina Kalabova
´ ˇ ˇ ˇ ´ ´ ´ ´ ˇ ´ ´
Department of Inorganic Chemistry, Institute of Chemical Technology, Technicka 5, 16628 Prague 6, Czech Republic
Abstract
We present a new approach of introducing erbium ions onto thin surface layers of silica glass substrates based on soaking of solution
3
+
0
of erbium complexes. Different types of Er
complexes with 2,2 -dipyridyle, 1,10-phenantroline, 8-hydroxyquinoline and
ethylendiamine ligands and nitrate, thiocyanate and acetate anions were prepared. Composition of the complexes was determined by
elementary analysis and by FT-IR spectroscopy. Decomposition temperature was measured by thermogravimetric analysis. Erbium
doped surface layers exhibit strong photoluminescence with maximum on 1533 nm and full width at half maximum above 50 nm.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: A. Glasses; A. Optical materials; B. Chemical synthesis; D. Luminescence; D. Optical properties
1
. Introduction
lower or even to avoid the risk of the RE clustering) with
the number of donor oxygen atoms kept as low as possible
(to avoid presence of the OH groups, which would shorten
Rare earths (RE) doped materials are of crucial
3
+
importance to photonics and are becoming to be widely
deployed in solid-state lasers. To avoid unwanted pair
interactions of the RE ions within the whole body of the
substrate it is needed to restrict the presence of them only
in the shallow surface layer; that is the localized doping is
highly desirable. Er is for this reason the most popular
RE ion [1], mainly for the characteristic emission around
1
some of the Er
excited states lifetimes) and (b) they
should allow for synthesizing in non-aqueous solutions (for
the same reason as above). Moreover, the complexes
should be decomposable by heating without leaving any
unwonted residues.
3
+
Synthesis and properties of RE complexes were broadly
studied in last decades. Syntheses of several RE complexes
with 1,10-phenantroline were reported [2–4]. Synthesis of
RE complex with ethylendiamine was carried out in
anhydrous acetonitrile [5] as well as anhydrous tetrachlor-
4
4
550 nm (coming from the I13/2- I
transition),
15/2
which is the wavelength currently used in telecommunica-
tions [1].
0
We present a new approach of introducing erbium ions
onto thin surface layers of glass substrates. The approach is
based on soaking of solutions of erbium coordination
compound (Er complexes) into porous silicate glass
followed by annealing to decompose the Er-complex and
to sinter the porous glass material. To achieve homo-
geneous distribution of erbium ions in the glass matrix the
fact that the presented method utilizes two advantages:
large molecules of the erbium complexes are spread in
regularly located micro or nano pores of the glass. The
synthesized erbium complexes should fulfill following
criteria: (a) they should have large ligands (to substantially
methane [4]. Several complexes of 2,2 -dipyridile ligands
were successfully synthesized in anhydrous ethanol [6].
Syntheses of 8-hydroxyquinoline complexes were reported
mainly in aqueous solutions [7,8].
2. Experiments and measurements
0
Erbium complexes with 2,2 -dipyridyle, 1,10-phenantro-
line, 8-hydroxyquinoline and ethylendiamine ligands were
prepared in anhydrous ethanol or isopropanol. Erbium
was obtained as their oxide of 99.9% purity from
0
Alchimica (Czech Republic). 2,2 -dipyridyl, 1,10-phenan-
trolin, 1,2-ethylendiamin, 8-hydroxyquinoline, and other
chemicals were obtained in analytical grade from Penta
(Czech Republic) and used without further purification.
Ã
Corresponding author. Tel.: +420 2204 44 286; fax: +420 2204 44 411.
E-mail address: zdenek.sofer@vscht.cz (Z. Sofer).
0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2007.01.003

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Z. Sofer et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1272–1275
1273
Analytical grade anhydrous ethanol was obtained from
Aldrich and used without further purification.
trihydrate (1.40 g, 10.3 mmol) in 50 ml of ethanol. The
mixture was cooled down and insoluble sodium nitrate was
filtered out. Filtrated solution was slowly added to a
solution of 1,10-phenantroline monohydrate (0.56 g,
2.8 mmol) in 20 ml of ethanol. The mixture was allowed
to stay for 24 h and the insoluble complex was filtered out.
The crystalline product was dried over P O . The yield
Sorption of Er complexes was performed on porous glass
substrates from saturated isopropanol solution. Sorbet
substrates were heated for several hours at 600 1C and then
the temperature was slowly increased to 1100 1C. Tem-
perature stability of the complexes was investigated by
thermogravimetric analysis (TGA) on commercial appara-
tus Redcrost TG-750. The range of TGA measurements
were from room temperature up to 850 1C. All TGA
measurements were carried out in air. Chemical composi-
tion was estimated by elementary analysis on ELEMEN-
TAR VARIO L3. The concentration of C, N, H and S were
determined. Photoluminescence (PL) spectra were mea-
sured in the range of 1440–1650 nm with 0.5 nm steps. The
semiconductor laser POL 4300 with pumping wavelength
4
10
was 70%. Trithiocyanato-tris-(1,10-phenantrolin) erbium
(III): A solution of erbium chloride hexahydrate (2.45 g,
6.4 mmol) in 50 ml ethanol was treated with potassium
thiocyanate (2.80 g, 28.8 mmol) in 150 ml ethanol. The
mixture was cooled down to 0 1C and precipitated
potassium chloride was filtered out. 1,10-phenantroline
monohydrate (5.10 g, 25.7 mmol) in 100 ml of ethanol was
added to filtrated solution. The mixture was allowed to stay
for 24 h and precipitated crystals were filtered out. The
crystalline product was dried over P O . The yield was
ꢀ
2
9
80 nm and power density 5 W cm was used for excita-
4
10
0
tion. All measurements were carried out at room tempera-
ture. FT-IR spectroscopy was performed on commercial
apparatus Nicolet 740. The potassium bromide disk
technique was used for recording of the FT-IR spectra.
We investigated solubility of prepared complexes in
common organic solvents. Erbium nitrate was prepared
by dissolving of erbium oxide in diluted nitric acid.
Solution of erbium nitrate was evaporated until crystal-
lization starts and then cools down. Crystals of erbium
nitrate pentahydrate were filtered out. Erbium chloride
hexahydrate was prepared in the same way.
75%. Trithiocyanato-tris-(2,2 -dipyridyl) erbium (III): A
solution of erbium chloride hexahydrate (2.45 g, 6.4 mmol)
in 50 ml ethanol was treated with potassium thiocyanate
(2.80 g, 28.8 mmol) in 150 ml ethanol. The mixture was
cooled down to 0 1C and precipitated potassium chloride
0
was filtered out. 2,2 -dipyridyl (3.50 g, 22.4 mmol) in 60 ml
of ethanol was added to filtrated solution. The mixture was
allowed to stay for 24 h and precipitated crystals
were filtered out. The crystalline product was dried over
P O . The yield was 71%. Trinitrato-tetrakis-(8-hydro-
4
10
xyquinoline) erbium (III): Erbium nitrate pentahydrate
(1.33 g, 3.0 mmol) was dissolved in 600 ml of water and
8-hydroxyquinoline (1.32 g, 13.6 mmol) was dissolved in
130 ml of ethanol. Erbium nitrate solution was heated to
70 1C and alkalized by ammonia on pH ꢁ9. The solution of
8-hydroxyquinoline was dropwise added to this vigorously
stirred solution of erbium nitrate. This solution was
allowed to stay for 5 h and then the precipitated complex
was filtered out. Product was dried for 3 h at 110 1C. The
yield was 68%. Trinitrato-tetrakis-ethylendiamin erbium
(III): A solution of erbium nitrate pentahydrate (2.21 g,
5.0 mmol) in 10 ml ethanol was treated with 1,2-ethylen-
diamin (3.01 g, 50 mmol) in 100 ml of tetrachlormethane.
The immediately formed precipitate was filtered out and
washed with tetrachlormethane. This light pink crystalline
solid is extremely hygroscopic. The yield was 66%.
0
Trinitrato-bis-(2,2 -dipyridyl) erbium (III): A solution of
erbium nitrate pentahydrate (2.25 g, 5.1 mmol) in 100 ml
0
isopropanol was treated with a solution of 2,2 -dipyridyl
(
2.04 g, 13.1 mmol) in 100 ml of isopropanol. Formation of
insoluble complex occurred after mixing of these two
solutions. The mixture was allowed to stay for 24 h and the
insoluble complex was filtered out. The crystalline product
was dried over P O . The yield was 95%. Trinitrato-bis-
4
10
(
1,10-phenantrolin) erbium (III): A solution of erbium
nitrate pentahydrate (1.20 g, 2.7 mmol) in 100 ml isopro-
panol was treated with a solution of 1,10-phenantroline
monohydrate (1.12 g, 6.0 mmol) in 100 ml of isopropanol.
The formation of crystalline compound occurred immedi-
ately. The mixture was allowed to stay for 24 h and then the
insoluble complex was filtered out. The crystalline product
was dried over P O . The yield was 94%. Tricetato-2,
4
10
0
2
-bipyridyl erbium (III): A boiling solution of erbium
3. Results and discussion
nitrate pentahydrate (1.40 g, 3.2 mmol) in 10 ml of ethanol
was treated with boiling solution of sodium acetate
trihydrate (1.40 g, 10.3 mmol) in 50 ml of ethanol. The
mixture was cooled down and insoluble sodium nitrate was
filtered out. Filtrated solution was slowly added to a
Syntheses of the erbium complexes are necessary to carry
out in anhydrous conditions. Ethylendiamine complex of
erbium is very hygroscopic and fast hydrolysis occurs in air
[9]. This synthesis must be made in non-alcoholic solution
because alcohol acts here as a ligand, too [9]. It is
important to know the temperature stability of complexes
for preparation of erbium doped glass from porous glass
substrates. Erbium complexes of 1,10-phenantroline and
0
solution of 2,2 -dipyridyl (0.49 g, 3.1 mmol) in 10 ml of
ethanol. The mixture was allowed to stay for 24 h and the
insoluble complex was filtered out. The crystalline product
was dried over P O . The yield was 71%. Triacetato-1,10-
4
10
0
phenantrolin erbium (III): A boiling solution of erbium
nitrate pentahydrate (1.40 g, 3.2 mmol) in 10 ml of ethanol
was treated with boiling solution of sodium acetate
2,2 -dipyridyl with nitrate, and thiocyanate anions were
well crystalline and thermal stable. Thermal stability
and decomposition temperature of the complexes were

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Z. Sofer et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1272–1275
1274
investigated by TGA. Temperatures of complexes decom-
position are summarized in Table 1. Two most stable
complexes contain thiocyanate anions; decomposition is
finished at temperature range 600–700 1C. Decomposition
temperature range of 8-hydroxyquinoline complex is very
broad, it starts at about 150 1C and is over 600 1C.
Chemical composition of prepared complexes was
investigated by elementary analysis and concentrations of
C, H, N and S were determined. The obtained values are in
good agreement for complexes of erbium with nitrate
anion. Some small disagreement between the observed and
calculated value was detected for the complexes with
acetate and thiocyanate anions. It is done by uncompleted
exchanging of these anions with starting salts, chloride for
thiocyanate and nitrate for acetate. Determination of exact
composition for ethylandiamine complex was problematic
due to hygroscopic behavior of this substance. The
nate group in thiocyanate complexes [6]. Splitting of this
absorption band indicates coordinated thiocyanate group
ꢀ
1
[4]. Strong absorption band at 1385 cm indicates ionic
nitrate group in nitrate complexes. We although observed
ꢀ
1
absorption bands in region about 1400 and 1600 cm
which are mainly attributed to CQN and CQC stretch-
ing vibration frequencies [10]. In the case of 8-hydro-
xyquinoline nitrate complex we observed absorption band
ꢀ
1
of ionic nitrate group at 1383 cm and also absorption
bands of coordinated nitrate group at 1319, 1466 and
ꢀ
1
ꢀ1
1498 cm . Absorption bands in region of 1100 cm are
related to the C–O stretching vibration energy and are
largely affected with the ionic potential of the cation [8,11].
Absorption bands of CQN and CQC stretching vibra-
tion were clearly observed on this complex. In the acetate
complexes, we observed strong split absorption bands of
OCO unsymmetrical strain vibration in the range from
ꢀ
1
8
-hydroxyquinoline complex still contained traces of water
1550 to 1600 cm . OCO symmetrical strain vibration
1
frequency was about 1450 cm [2].
ꢀ
which are difficult to eliminate without its decomposition.
Table 2 gives the results from elementary analysis and their
comparison with theoretical values on. Solubility of
complexes was tested in several commonly used organic
solvents. They are insoluble in aliphatic hydrocarbons and
ethers, slightly soluble in alcohols and aromatic hydro-
carbons, like toluene and xylene, and halogen derivates of
hydrocarbons. The highest solubility was observed in
dimethylformamide.
PL are shown in Fig. 1. Maximum intensity was at
1533 nm. Higher PL intensity was observed for fabricated
optical layer using complexes with 1,10-phenantroline and
8-hydroxyquinoline ligands. The sample fabricated by
soaking with triacetato-1,10-phenantrolin erbium(III) ex-
hibited the highest PL intensity. The value of FWHM (full
width at half maximum) at 1533 nm is above 50 nm.
ꢀ
1
A broad absorption band about 3400 cm from water
was observed in all FT-IR-spectra. We observed strong
T = 300 K
[(phen)Er](ac)3
1
1
1
4000
2000
0000
ꢀ
1
absorption band on 2063 cm from stretching of thicaya-
λex = 980 nm
[(dipy)3Er](SCN)3
[(hq) Er](NO )
3 3 3
Table 1
Temperature stability of Er complexes
[(dipy)Er](ac)3
8
6
4
2
000
000
000
000
Complex
Starting temperature The final
of decomposition temperature of
1C)
(
decomposition (1C)
0
[
[
[
[
[
[
[
(2,2 -dipy) Er](NO
(1,10-phen)
2
3
)
3
200
300
200
150
200
200
220
470
550
500
650
450
700
600
2
Er](NO )
3 3
0
(2,2 -dipy)Er](ac)
3
0
1
(8-hq)
4 3 3
Er](NO )
450
1500
1550
Wavelength [nm]
1600
1650
(1,10-phen)Er](ac)
3
(1,10-phen)
0
3
Er](SCN)
3
(2,2 -dipy)
3
Er](SCN)
3
Fig. 1. Photoluminescence of erbium doped glass substrates.
Table 2
Results of elementary analysis
Complex
% N Theor.
% N Exp.
% C Theor.
% C Exp.
% H Theor.
% H Exp.
% S Theor.
% S Exp.
0
[
[
[
[
[
[
[
[
(2,2 -dipy) Er](NO
(1,10-phen)
2
3
)
3
14.73
13.74
5.60
14.83
13.71
6.084
6.93
36.09
40.39
38.39
51.24
41.21
16.19
53.10
48.93
35.99
40.02
35.20
51.72
40.55
14.74
50.28
38.23
2.420
2.260
3.420
3.344
3.266
5.430
2.742
2.986
2.434
2.314
2.982
3.061
3.134
5.273
2.869
2.855
0.00
0.00
0.00
0.00
2
Er](NO )
3 3
0
(2,2 -dipy)Er](ac)
3
0.00
0.00
(8-hq)
(1,10-phen)Er](ac)
(en) Er](NO
4
Er](NO
3
)
3
6.64
5.34
0.00
0.00
0.00
0.00
3
5.50
4
3
)
3
25.95
14.29
15.56
23.60
14.17
13.40
0.00
10.90
11.87
0.00
10.75
12.89
(1,10-phen)
0
3
Er](SCN)
3
(2,2 -dipy)
3
Er](SCN)
3

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Z. Sofer et al. / Journal of Physics and Chemistry of Solids 68 (2007) 1272–1275
1275
4
. Conclusion
References
[
[
[
1] A.J. Kenyon, Prog. Quantum Electron. 26 (2002) 225–284.
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were prepared. These complexes were characterized by FT-
IR spectroscopy and elementary analysis. Decomposition
was studied by thermogravimetric analysis. Glass sub-
strates doped by erbium complex were studied by photo-
luminescence measurements with pumping wavelength of
80 nm. The best result was obtained for triacetato-1,
0-phenantrolin erbium(III). The sample fabricated by
soaking with triacetato-1,10-phenantrolin erbium(III) had
the value of FWHM at 1533 nm above 50 nm, which is
sufficient for practical utilization.
4143–4151.
4] F.A. Hart, F.P. Laming, J. Inorg. Nucl. Chem. 26 (1964) 579–585.
[
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[
[
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Spectrochim. Acta 8 (1956) 1–8.
9
1
[
8] H.F. Aly, F.M.A. Kerim, A.T. Kandil, J. Inorg. Nucl. Chem. 33
(
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[
[
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Spectrochim. Acta 8 (1956) 1.
Acknowledgment
The research has been supported by the GACR project
06/05/0706 and 102/03/D041. We thank Alchimica
1
Company for supplying the erbium oxide.