The studies of enhanced fluorescence in the two novel ternary rare-earth complex systems

Article abstract of DOI:10.1007/s10895-009-0567-7

Two novel ternary rare-earth complexes SmL₅?L? (ClO₄)₂?7H₂O and EuL₅? L^'? (ClO₄)₂?6H₂O (the first ligand L = C₆H₅ COCH₂SOCH

Full text of DOI:10.1007/s10895-009-0567-7

J Fluoresc (2010) 20:453–461
DOI 10.1007/s10895-009-0567-7
ORIGINAL PAPER
The Studies of Enhanced Fluorescence in the Two Novel
Ternary Rare-Earth Complex Systems
Xiao-Jun Sun & Wen-Xian Li & Wen-Juan Chai &
Tie Ren & Xiao-Yan Shi
Received: 1 September 2009 /Accepted: 3 November 2009 /Published online: 18 November 2009
#
Springer Science + Business Media, LLC 2009
Abstract Two novel ternary rare-earth complexes
Introduction
’
’
SmL5·L ·(ClO4)2·7H2O and EuL5·L·(ClO4)2·6H2O (the first
ligand L = C6H5COCH2SOCH2COC6H5, the second ligand
L’ = C6H4OHCOO−) were synthesized and characterized by
element analysis, molar conductivity, coordination titration
analysis, IR, TG-DSC, 1HNMR and UV spectra. The
detailed luminescence studies on the rare-earth complexes
showed that the ternary rare-earth complexes presented
stronger fluorescence intensities, longer lifetimes, and higher
fluorescence quantum efficiencies than the binary rare-earth
materials. After the introduction of the second ligand salicylic
acid group, the relative emission intensities and fluorescence
In the last decades, many lanthanide complexes were noted
for their interesting photophysical properties arising from f–f
transitions and were used as candidates for a number of
applications, such as electroluminescence devices and photo-
luminescence devices, and were used as probes and labels in a
variety of biological and chemical applications [1–6]. And the
usage based on samarium and europium ions were of
special interest due to their unique fluorescence properties,
such as long fluorescent decay time, narrow emission bands
and strong fluorescence electron excited states. Since the f–
f transitions were spin-forbidden, the strong fluorescence
was attributed to appropriate energy transfer from the
photon-excited chromophores (organic ligand) to the rare-
earth ions [7]. In rare-earth complexes, the organic ligand
had abilities of absorbing and transferring energy [8]
efficiently to the rare-earth ions (intra-molecular energy
transfer). Consequently the luminescence intensity of rare-
earth ions was increased. As a new organic ligand, the
sulfoxide ligand had superb coordination ability and their
rare-earth complexes had advantage of good solubility, high
stability and strong luminescence intensities. In the past
several decades, many sulfoxide complexes had been
synthesized and intensively studied due to their special
fluorescence properties [9, 10]. Thus, as we had noted, a
ligand bis(benzoylmethyl) sulfoxide which had two carbonyl
groups ,large conjugated plane and rigid structure was
chosen in the paper.
’
lifetimes of the ternary complexes LnL5·L ·(ClO4)2·nH2O
(Ln = Sm, Eu; n=7, 6) enhanced more obviously than the
binary complexes LnL5·(ClO4)3·2H2O. This indicated that
the presence of both organic ligand bis(benzoylmethyl)
sulfoxide and the second ligand salicylic acid could sensitize
fluorescence intensities of rare-earth ions, and the introduc-
tion of salicylic acid group was a benefit for the fluorescence
properties of the ternary rare-earth complexes. The fluores-
cence spectra, fluorescence lifetime and phosphorescence
spectra were also discussed.
.
Keywords Ternary rare-earth complexes Fluorescence
.
.
enhancement Phosphorescence Fluorescence lifetime
Many studies showed that the emission intensities and
fluorescence lifetimes of ternary rare-earth complexes were
enhanced obviously after introducing the second organic
ligand [11, 12]. The second organic ligand served as the
energy donor and enhanced the fluorescence intensities of
binary rare-earth complexes. The effect was called “synergis-
:
:
:
:
X.-J. Sun W.-X. Li (*) W.-J. Chai T. Ren X.-Y. Shi
College of chemistry and chemical engineering,
Inner Mongolia University,
Hohhot 010021, People’s Republic of China
e-mail: nmglwx@163.com

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J Fluoresc (2010) 20:453–461
Fig. 1 The synthesis scheme of bis(benzoylmethyl) sulfoxide
tic effect” [13]. Furthermore, the introduction of the second
organic ligand would not only reinforce the fluorescence
emission intensities, but also fulfilled the coordination
numbers of rare-earth complexes. Because of its excellent
coordination ability to rare-earth ions and the ability of
sensitizing the luminescence of rare-earth ions, salicylic acid
had been applied to many ternary rare-earth systems [14, 15].
For this reason, salicylic acid was chosen as the second
organic ligand in ternary rare-earth complexes in this paper.
Thus, in order to seek new fluorescence materials and study
the effects of the second ligand (salicylic acid) on the
fluorescence properties of rare-earth complexes, the ternary
rare-earth complexes SmL5·L’·(ClO4)2·7H2O and
Fig. 2 The TG-DSC curves of SmL5 ·L’ · (ClO4)2·7H2O
SDTQ600 differential scanning calorimeter and thermal
gravimetric analyzer. The infrared spectra (IR, ν=4,000–
400 cm−1) were determined by the KBr pressed disc
method on a Nicolet NEXUS-670 FT-IR spectrophotome-
ter. The ultraviolet spectra (190–400 nm) of the ligands and
the ternary complexes were recorded on a Shimadzu TU-
1901 double beam spectrophotometer and DMF was used
’
EuL5·L·(ClO4)2·6H2O (the first ligand L = C6H5COCH2-
’
SOCH2COC6H5, the second ligand L = C6H4OHCOO−) had
been synthesized by the reaction of bis(benzoylmethyl)
sulfoxide and salicylic acid with Sm (III) and Eu (III)
respectively and characterized by IR spectra, chemical
analysis and elemental analysis. We had also studied the
fluorescence properties of the ternary Sm (III), Eu (III)
complexes in solid state.
1
as a reference and solvent. HNMR spectra were measured
on Bruker AC-300 spectrometer in CDCl3. Fluorescence
excitation and emission spectra were determined on a
Hitachi RF-3010 fluorescence photometer with the slit
width was 3 nm. The phosphorescence spectra were
monitored by F-4500 FL spectrophotometer at room
temperature. Fluorescent decay curves were recorded by
FLS920 Combined Steady State and Lifetime Spectrometer.
Experiment
Materials
Synthesis of ligand
The purity of lanthanide oxide exceeds 99.99%, the rare-
earth (III) perchlorates were prepared by dissolving their
oxide (99.99%) in HClO4 (2 mol/L). All other chemicals
used were of analytical grade.
The synthesis scheme was shown in Fig. 1.
Bis(benzoylmethyl) sulfide was dissolved in acetic acid
and 30% hydrogen peroxide was added to it at once. The
mixture was stirred continuously at room temperature for
24 h. After the reaction stopped, the mixture was extracted
with anhydrous ether until the pH of mixture was 7. Then
the white solid was precipitated, filtered and dried in
Physical measurements
Elemental analysis was carried out on a PE-2400 analyzer.
Conductivity measurement was made using a 10−3 mol ·L−1
solution in DMF on a DDS-11D conductivity meter at room
temperature. Rare-earth contents of the complexes were
determined by EDTA titration using Xylenol-orange as
indicator. The thermal behavior was monitored on
1
vacuum. Yield: 95%, mp: 110–111 °C. HNMR (CDCl3,
300 MHz) δ(ppm): 7.509–8.025 (10H, m, ArH), 4.421–
4.820 (4H, s, CH2). Anal. calcd. for C16H14SO3: C, 67.1%;
H, 4.90%; Found: C, 66.6%; H, 4.68%.
Table 1 Composition analysis
Complexes
M
Anal.calcd.(found)(%)
1m
(%) and molar conductivities
(S·cm2·mol−1) of the ternary
rare-earth complexes (25°C)
C
H
RE
SmL5·L’·(ClO4)2·7H2O
EuL5·L’·(ClO4)2·6H2O
2,042
2,026
50.99 (51.11)
51.30 (51.53)
4.31 (4.36)
4.20 (4.29)
7.25 (7.36)
7.51 (7.50)
190.9
196.5

J Fluoresc (2010) 20:453–461
455
first ligand L = C6H5COCH2SOCH2COC6H5, the second
ligand L’ = C6H4OHCOO−) respectively. The 1m values of
the complexes in DMF were in accordance with the formula
−
as 1:2 electrolytes [16], two ClO4 ions were not bonded
with rare-earth ions. The complexes were white powder,
stable in atmospheric condition and soluble in acetone,
DMF and CDCl3.
TG-DSC studies
The TG-DSC analysis was carried out up to 1,000 °C in N2
with heating rate of 10 °C· min−1 and TG-DSC curves of
the ternary Sm (III), Eu (III) complexes were depicted in
Figs. 2 and 3 respectively. Figures 2 and 3 showed the first
weight loss on TG curves from 59.78 °C to 133.34 °C
for the ternary Sm (III) complex and from 54.61 °C to
133.86 °C for Eu (III) complex, the percentage of weight
loss were 5.15% and 4.38% respectively which was
coinciding with the lose numbers of water in ternary
complexes. At the same time, there was an endothermic
peak at about 60 °C in DSC curves. The comparatively
low temperature of water loss showed that they were
crystal water. In addition, two obvious weight loss peaks
had taken place in TG curves which attributed to the
decomposition of three sulfoxide ligands, and two
sulfoxide ligands and phenyl group, respectively. Mean-
time, two large endothermic bands occurred at about
150 °C and 230 °C on DSC curves. The last weight
loss in TG curves was found to coincide with the
decomposition of [(ClO4)2] 2−. The final product was
found to be LnCl (CO3) when the temperature was
approximately 1,000 °C and the total weight loss of the
complexes was close to the calculated values. The results
were coinciding with element analysis.
Fig. 3 The TG-DSC curves of EuL5·L’ · (ClO4) ·6H2O
2
Synthesis of the ternary rare-earth complexes
The mixture of 5 mmol bis(benzoylmethyl) sulfoxide and
1 mmol salicylic acid was dissolved in anhydrous ethanol,
then the anhydrous ethanol solution (3 ml) of 1 mmol Ln
(ClO4)3·nH2O (Ln = Sm, Eu) was added dropwise to it.
After stirred for 4 h at room temperature, the precipitate
was separated from the solution by suction filtration,
purified by washing for several times with anhydrous ether,
and dried for 24 h in a vacuum (yield >90%).
Results and discussion
Elemental analysis and molar conductivity values were
given in Table 1, and the composition of ternary complexes
was SmL5·L’·(ClO4)2·7H2O and EuL5·L’·(ClO4)2·6H2O (the
Fig. 4 Infrared absorption spec-
trum of bis(benzoylmethyl)
sulfoxide

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J Fluoresc (2010) 20:453–461
Fig. 5 Infrared absorption spec-
trum of sodium salicylate
Infrared spectra
coordination, there were no significant shifts, which
suggested that the oxygen atom in the carbonyl group was
not coordinated with rare-earth ions. The characteristic
absorption bands of benzene appeared at approximately
The IR spectra of the ligand (bis(benzoylmethyl) sulfoxide,
sodium salicylate) and the ternary rare-earth complexes
were recorded and the important IR assignments could be
seen in the Figs. 4, 5, 6 and Table 2. The spectra of the
ternary Sm (III), Eu (III) complexes were similar.
Figure 6 showed the disappearance of the band at the
1,033 cm−1 (ν S = O) and the existence of band at 991 cm−1
(ν S = O), which indicated that rare-earth ions were bonded
with oxygen atom in sulfonyl group. The C = O stretching
vibration frequency of the ligand appeared at 1,676 cm−1
and it was the strongest absorption in Fig. 4. After
3,060 cm−1 C-H), 1,597 cm−1 C=C), 755 cm−1 (δ C-H) and
( (
685 cm−1 (δ C-H) in the Fig. 4 and they were also found in
the spectra of ternary Eu (III) complex.
−
−
The ν
and ν
absorption of sodium
s(COO )
as(COO )
salicylate occurred at 1,584 and 1,380 cm−1, and the Δν
value was 204 cm−1 in the Fig. 5. There were no significant
bands between 1,690 and 1,730 cm−1 in the spectra of
ternary rare-earth complexes indicated that carboxyl group
−
had taken place deprotonation. The presence of ν
as(COO )
Fig. 6 Infrared absorption spec-
trum of EuL5·L’ · (ClO4) 2·6H2O

J Fluoresc (2010) 20:453–461
457
Table 2 Some main IR data of ligands and the ternary rare-earth
complexes
only one absorption band at 266 nm in the absorption
spectra of (c) Sm (III) and (d) Eu (III) complex. This
resulted a blue-shift of the major π-π* electronic transition
(from 303 nm to 266 nm) for salicylic acid, indicating that
the energy of the π* orbits increased after oxygen atom of
salicylic acid coordinated with rare-earth ions.
Assignment(cm−1
)
Bis
Sodium
Sm (III) Eu (III)
(benzoylmethyl) salicylate complex complex
sulfoxide
ν
ν
ν
δ
O-H(H2O)
C=C(C6H5)
C-H(C6H5)
C-H(C6H5)
–
3,446
3,446
1,599
3,066
755
3,446
1,597
3,066
755
1,597
3,060
755
685
1,033
1,676
2,971
1,448
–
1,599
1HNMR spectra
–
–
1
The HNMR spectra data of bis(benzoylmethyl) sulfoxide,
–
686
686
salicylic acid and the ternary rare-earth complexes could be
ν
ν
ν
δ
–
991
991
S=O
1
seen from the Table 3. The HNMR of bis(benzoylmethyl)
–
1,671
2,965
1,449
1,084
626
1,675
2,965
1,449
1,087
628
C=O
sulfoxide ligand in CDCl3 showed two classificatory
hydrogen proton resonance peaks which belonged to
phenyl and methylene group appeared at δ7.247–8.015
and δ4.404–4.801 ppm, and the ratio of resonance peaks
area was 10:4. There were multiple hydrogen bonds
between hydroxyl and carboxyl group in ligand salicylic
acid, so the proton resonance peak of phenolic hydroxyl
group was at δ10.34 ppm which was the average value of
carboxyl and phenolic hydroxyl group. The 1HNMR
spectra of the ternary rare-earth complexes were similar.
The proton resonance peaks of phenyl and methylene group
were very clear, which had shifted at different degree. The
reason may be concerned with coordinate effect. The proton
resonance peak of carboxyl group disappeared, suggested
C-H(CH2)
–
C-H(CH2)
–
−
ν
(ClO4
)
–
Cl-O
−
δ(ClO4
)
–
–
δO-H (phenolic
–
1,483
1,467
1,472
hydroxyl group)
ν
S(COO−)
as(COO−)
–
–
1,380
1,584
1,400
1,640
1,400
1,635
ν
−
and ν
absorption bands at 1,635 and 1,400 cm−1 in
s(COO )
the ternary rare-earth complexes and the Δν value was
239 cm−1 greater than that of sodium salicylate, which
could be deduced that carboxyl group was coordinate with
rare-earth ions by mono-dentate type [17]. According to the
reference [18], the characteristic absorption band of the δ O-H
(phenolic hydroxyl group) stretching vibration mode
appeared at 1,483 cm−1. We could draw the conclusion that
rare-earth ions were bonded with oxygen atom in phenolic
hydroxyl group when there was an obvious shift of the δ O-H
stretching frequency towards lower wave number by
11 cm−1 in ternary Eu (III) complex. When ClO4 was not
−
coordinated, it was Td symmetry and there were two
−
absorption bands. When ClO4 was coordinated, it was C3v
symmetry and there were five absorptions [19, 20]. In the
spectra of the ternary rare-earth complexes, two absorption
bands could be seen clearly at approximately 1,087 and
628 cm−1. Therefore, ClO4 was Td symmetry. In terms of
−
−
molar conductivities, it could be suggested that two ClO4
were not bonded with rare-earth ions.
UV absorption spectra
The UV absorption spectra of (a) bis(benzoylmethyl)
sulfoxide, (b) salicylic acid, (c) the ternary Sm (III)and (d)
Eu (III) complexes were recorded in Fig. 7 and DMF was
used as a reference and solvent. In Fig. 7 (a) and (b), the
major band of π-π* electronic transition in phenyl group
was observed at 266 and 303 nm, respectively. There was
Fig. 7 The UV absorption spectra of a bis(benzoylmethyl) sulfoxide,
b salicylic acid, c the ternary Sm (III) and d Eu (III) complexes

458
Table 3 Chemical shift data of HNMR spectra (1×10−6
J Fluoresc (2010) 20:453–461
1
)
Ligands and complexes
1HNMR (ppm)
-CH2-
-COOH-
-OH-
-C6H5-
L: C6H5COCH2SOCH2COC6H5
L’: C6H4OHCOOH
4.401~4.801(s, 4H)
–
–
–
7.247~8.015(m, 10H)
6.913~7.917(m, 4H)
7.243~7.766(m, 10H)
7.236~8.160 (m, 10H)
10.34 (s, H)
10.34(s, H)
SmL5·L’·(ClO4)2·7H2O
EuL5·L’·(ClO4)2·6H2O
5.241~5.339(s, 4H)
2.787~3.668(s, 4H)
–
–
–
–
that there was coordinated reaction between salicylic acid
group and rare-earth ions in the ternary rare-earth com-
plexes. A broad proton resonance peak was found between
δ7.236 and δ8.160 ppm, which indicated the phenyl group
absorption peak of bis(benzoylmethyl) sulfoxide overlap-
ped with that of salicylic acid group.
the ligand in complexes (Fig. 7c and d). The strong
emission intensities between 250 to 350 nm indicated that
both ligands were good organic ligand which were
beneficial to absorb energy and transfer it to Sm (III), Eu
(III) ions, and emitted the characteristic fluorescence of Sm
(III), Eu (III) ions [21].
The emission lines of the ternary Sm (III) complex
4
6
Luminescence properties
(Fig. 8a) were assigned to G5/2 → FJ (J = 5/2 and 7/2)
transitions of Sm (III) at 564 and 601 nm, respectively, and
the strongest fluorescence emission intensity at 601 nm
which was considered to the characteristic emission for the
Fluorescence spectra of the ternary rare-earth complexes
6
The excitation and emission spectra of the ternary Sm (III),
Eu (III) complexes in solid state at room temperature were
measured. Figure 8a and b showed the excitation and
emission spectra of the ternary Sm (III), Eu (III) complexes
respectively. The excitation spectra were obtained by
monitoring the emission of the Sm (III) complex at
601 nm and Eu (III) complex at 618 nm. Both of the
systems had similar excitation spectra which were domi-
nated by a broad band from 250 to 450 nm with the
maximum peak at 327 nm. Meantime, in spectra of the
ternary Sm (III), Eu (III) complexes, there was a wide
excitation band from 200 to 400 nm and the excitation band
could overlap effectively with UV absorption spectrum of
4G5/2 → F7/2 transition of the Sm (III) ion. In Fig. 8b,
The emission lines of Eu (III) complex were assigned to
the transitions of Eu (III) at 539 (5D1-7F0), 557 (5D1-7F1),
596 (5D0-7F1), 618 (5D0-7F2) and 702 (5D0-7F4) nm. The
fluorescence emission spectrum of the ternary Eu (III)
complex under the excitation of 327 nm showed the
strongest emission peak at 618 nm which corresponded
with the characteristic emission for the D0-7F2 transition
5
of the Eu (III) ion. The 5D0-7F2 transition was electric
dipole transition, which could be detected as a relatively
strong peak when Eu (III) wasn’t locate the centrosym-
metric ligand field and gave off the red luminescence. The
5D0
→
7F1 transition was magnetic dipole transition,
Fig. 8 Fluorescent excitation
and emission Spectra of ternary
Sm (III) (a) and Eu (III) (b)
complexes

J Fluoresc (2010) 20:453–461
459
Table 4 Comparison of fluorescent emission spectra data of binary
and ternary complexes
Complexes
1EX (nm) 1EM (nm) I (a.u.) Energy state
transitions
4
SmL5(ClO4)3·2H2O
SmL5·L’· (ClO4)2·7H2O
EuL5(ClO4)3·2H2O
338
327
332
327
601
601
618
618
18.63 G5/2→6H7/2
4
26.02 G5/2→6H7/2
813.4 5D0→7F2
918.6 5D0→7F2
EuL5·L’· (ClO4)2·6H2O
Fig. 9 Linear fit curve of the Sm (III) complex
second ligand (salicylic acid) on the luminescence
intensities of the binary rare-earth complexes, the
fluorescence spectrum data of the binary rare-earth
complexes were measured under similar conditions and
listed in Table 4. The characteristic emission lines of
complexes were similar. However, the ternary rare-earth
complexes present stronger luminescent intensities than
the binary rare-earth materials after introduction of the
second organic ligand salicylic acid. The strongest
characteristic emission intensity of the ternary Sm (III),
Eu (III) complexes was 26.02 (a.u.) and 918.6 (a.u.)
respectively, which was 1.4 and 1.37 times as great as
that of the binary Sm (III), Eu (III) complexes. The
reason may be concerned with the intra-molecular energy
transfer process between salicylic acid and Sm (III), Eu
(III) ions. The salicylic acid with a broad triplet state
energy level was thought to be a good synergistic ligand.
Furthermore, there was a wide excitation band and the
excitation band could overlap effectively with UV
absorption spectrum of the ligand in ternary rare-earth
complexes. The presence of salicylic acid was benefit to
absorb energy effectively and transfer it to Sm (III), Eu
(III) ions, emitting the characteristic fluorescence of Sm
(III), Eu (III) ions.
which became the strongest emission only if Eu (III) ion was
in the center of inversion [22]. Furthermore, the intensity ratio
7
5
7
of the two transitions (5D0 → F2 / D0 → F1) was about
2.58; we could conclude that the Eu (III) was not at the
center of an asymmetric coordination field. In order to study
the relationship between fluorescence intensity and fluores-
cence lifetime, the fluorescence decay curves of the ternary
Sm (III), Eu (III) complexes were measured. Figures 9 and
10 showed the linear fit curves of the ternary Sm (III), Eu
(III) complexes. The fluorescence lifetime values of Sm (III),
Eu (III) complexes were calculated by the single exponential
mode. From these results, both of the complexes with more
preferable fluorescence lifetimes and the fluorescence life-
time of Sm (III) complex (1,763 µs) was longer than that of
Eu (III) complex (1,258 µs).
The fluorescence properties comparison between the binary
and the ternary rare-earth complexes
As we had pointed earlier, the fluorescence properties of
rare-earth complexes were related to the second organic
ligand significantly. In order to study the effect of the
Fig. 11 The phosphorescence spectrum of bis(benzoylmethyl) sulfoxide
Fig. 10 Linear fit curve of the Eu (III) complex

460
J Fluoresc (2010) 20:453–461
earth complexes had better fluorescence properties than the
binary rare-earth complexes as a result.
Conclusion
Two novel ternary Sm (III), Eu (III) complexes had been
successfully synthesized and characterized. The composi-
tion of the ternary complexes was proved to be
SmL5·L’·(ClO4)2·7H2O and EuL5·L’·(ClO4)2·6H2O (the first
ligand L = C6H5COCH2SOCH2COC6H5, the second ligand
L’ = C6H4OHCOO−). The photophysical properties of the
complexes had been studied with ultraviolet spectra,
phosphorescence spectra, excitation and emission spectra,
fluorescence lifetimes and phosphorescence spectra. The
solid ternary complexes emitted characteristic emission of
Sm (III), Eu (III) ions and the fluorescence lifetime of Sm
(III) complex (1,763 µs) was longer than that of Eu (III)
complex (1,258 µs). The emission intensities and fluores-
cence lifetimes of ternary Sm (III), Eu (III) complexes
enhanced obviously after introducing the second organic
ligand salicylic acid. The introduction of the second organic
ligand had an effect on the fluorescence intensity of rare-
earth organic complexes. Hence, based on the factor, more
fluorescence materials could be obtained.
Fig. 12 The phosphorescence spectrum of salicylic acid
Phosphorescence spectra
The phosphorescence spectra of ligands (bis(benzoyl-
methyl) sulfoxide and salicylic acid) were recorded by F-
4500 FL spectrophotometer in solid state and listed in
Figs. 11 and 12. According to the energy transfer and intra-
molecular energy transfer mechanism [23, 24], intra-
molecular energy transfer efficiency chiefly depended on
two energy transfer processes: one was the transitions from
the triplet state energy level of ligand to the excited states of
the Sm (III) and Eu (III) ion by Dexter’s resonant exchange
interaction [25], the other was just an inverse energy
transfer process by the thermal deactivation mechanism
[26]. Based on this theory, we could draw the conclusion
that energy difference was of opposite influence on the two
energy transfer processes and the optimal value of energy
states could be calculated from the spectra. In Fig. 11, two
bands could be seen clearly at 575 and 475 nm which
corresponded to the triplet state energy level of bis
(benzoylmethyl sulfoxide T1 ( 18,349 cm−1) and T2
(21,053 cm−1), respectively. The triplet state energy level
Acknowledgements This work was supported by the financial
supports from the National Natural Science Foundations of China
Research project (20861005).
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T1 which was appropriately higher than G5/2 of Sm (III)
ion (17,900 cm−1) [27] and 5D0 of Eu (III) ion
(17,241 cm−1) [28] played an important role in transferring
energy process from bis(benzoylmethyl sulfoxide to rare-
earth ions. Figure 12 showed that the triplet state energy
level of the second ligand salicylic acid at 525 nm was
close to 19,408 cm−1, which was also higher than G5/2 of
4
5
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