Near-infrared luminescent hybrid materials doped with lanthanide (Ln) complexes (Ln = Nd, Yb) and their possible laser application

Article abstract of DOI:10.1021/jp044591h

The crystal structures of ternary Ln(DBM)₃phen complexes (DBM = dibenzoylmethane, phen = 1,10-phenanthroline, and Ln = Nd, Yb) and their in situ syntheses via the sol-gel process are reported. The properties of the Ln(DBM)₃phen complexes and their corresponding Ln³⁺/DBM/ phen-co-doped luminescent hybrid gels obtained via an in situ method (Ln-D-P gel) have been studied. The results reveal that the lanthanide complexes are successfully in situ synthesized in the corresponding Ln-D-P gels. Both Ln-(DBM)₃phen complexes and Ln-D-P gels display sensitized near-infrared (NIR) luminescence upon excitation at the maximum absorption of the ligands, which contributes to the efficient energy transfer from the ligands to the Ln³⁺ ions (Ln = Nd, Yb), an antenna effect. The radiative properties of the Nd³⁺ ion in a Nd-D-P gel are discussed using Judd-Ofelt analysis, which indicates that the ⁴F_3/2 a?? ⁴I_11/2 transition of the Nd³⁺ ion in the Nd-D-P gel can be considered as a possible laser transition. ? 2005 American Chemical Society.

Full text of DOI:10.1021/jp044591h

6174
J. Phys. Chem. B 2005, 109, 6174-6182
Near-Infrared Luminescent Hybrid Materials Doped with Lanthanide (Ln) Complexes
(Ln ) Nd, Yb) and Their Possible Laser Application
Li-Ning Sun,†,‡ Hong-Jie Zhang,*,† Qing-Guo Meng,† Feng-Yi Liu,† Lian-She Fu,†
Chun-Yun Peng,†,‡ Jiang-Bo Yu,†,‡ Guo-Li Zheng,†,‡ and Shu-Bin Wang†
Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, People’s Republic of China, and
Graduate School of the Chinese Academy of Sciences, People’s Republic of China
ReceiVed: NoVember 29, 2004; In Final Form: January 31, 2005
The crystal structures of ternary Ln(DBM)3phen complexes (DBM ) dibenzoylmethane, phen ) 1,10-
phenanthroline, and Ln ) Nd, Yb) and their in situ syntheses via the sol-gel process are reported. The
properties of the Ln(DBM)3phen complexes and their corresponding Ln3+/DBM/phen-co-doped luminescent
hybrid gels obtained via an in situ method (Ln-D-P gel) have been studied. The results reveal that the
lanthanide complexes are successfully in situ synthesized in the corresponding Ln-D-P gels. Both Ln-
(DBM)3phen complexes and Ln-D-P gels display sensitized near-infrared (NIR) luminescence upon excitation
at the maximum absorption of the ligands, which contributes to the efficient energy transfer from the ligands
to the Ln3+ ions (Ln ) Nd, Yb), an antenna effect. The radiative properties of the Nd3+ ion in a Nd-D-P
gel are discussed using Judd-Ofelt analysis, which indicates that the 4F3/2 f 4I11/2 transition of the Nd3+ ion
in the Nd-D-P gel can be considered as a possible laser transition.
1. Introduction
emission. Provided that most of the excitation energy is
transferred from the antenna chromophore to the central
luminescent lanthanide ion, this process is much more effective
than direct excitation, since the absorption coefficients of organic
chromophores are many orders of magnitude larger (typically
3-5) than the intrinsically low molar absorption coefficients
of trivalent lanthanide ions.10
However, due to poor photostability and thermal stability,
these light-emitting compounds have to be embedded into a
matrix for practical applications. Sol-gel hybrid materials
composed of both inorganic and organic components enable both
inorganic and organic dopants to be incorporated with relatively
high stability.11 Therefore, sol-gel hybrid materials are potential
candidates for practical applications. The sol-gel glasses doped
with lanthanide complexes are transparent and have good
mechanical properties, except these materials have some
drawbacks, such as the low solubility of lanthanide complexes
in the sol-gel matrix at the low pH needed for the hydrolysis
reaction.12 Qian et al.13 reported the in situ synthesis technique
and succeeded in doping lanthanide complexes into sol-gel
glass at a molecular level and with a high concentration by using
the technique. Therefore, in this work, the in situ approach was
selected to synthesize the neodymium and ytterbium complexes
in sol-gel materials, respectively.
In this paper, we report the structures of Ln(DBM)3phen
complexes (DBM ) dibenzoylmethane, phen ) 1,10-phenan-
throline, and Ln ) Nd, Yb) and the syntheses of homogeneous
transparent hybrid gels containing the corresponding lanthanide
complexes via the in situ approach (Ln-D-P gel). At the same
time, the properties of the Ln(DBM)3phen complexes and Ln-
D-P gels were investigated by FT-IR, diffuse reflectance (DR),
and luminescence spectra. A model of the indirect excitation
mechanism is suggested. Accordingly, the energy transfer from
the ligands to the central Ln3+ ions (Ln ) Nd, Yb) as well as
the NIR luminescence of the Ln3+ ions is discussed. The optical
The trivalent lanthanide ions have been known for their
unique optical properties such as line-like emission spectra and
high-luminescence quantum efficiency.1 Historically, detailed
research has been almost exclusively devoted to europium and
terbium luminescence.2 Recently, much attention has been paid
to near-infrared (NIR) luminescence of lanthanide ions, which
are emissive in the near-infrared region of the spectrum (800-
1700 nm), particularly neodymium3 and ytterbium.4 There are
two particular driving forces for this recent interest in NIR
luminescence. First, Nd-containing systems have been regarded
as the most popular infrared luminescent materials for applica-
tion in laser systems (the basis of the common 1064 nm laser).5
Second, the relative transparency of human tissue at ap-
proximately 1000 nm suggests that in vivo luminescent probes
operating at this wavelength (Yb-based emission) could have
diagnostic value.6 Therefore, developing strongly luminescent
NdIII and YbIII centers in these systems has been an attractive
target.
Since Weissman discovered that in the lanthanide complex
the excitation may be accomplished, under suitable conditions,
through light absorption by other constituents of the rare earth
compound, with subsequent transfer of energy to the rare earth
ion,7 numerous lanthanide complexes have been studied in
detail.8 The formation of complex between a lanthanide ion and
a certain organic ligand has a double beneficial effect on both
protecting metal ions from vibrational coupling and increasing
the light absorption cross section by “antenna effects”.9 The
energy transfer from organic chromophores to lanthanide ions
provides an effective way to excite the long-lived, sharply spiked
* Author to whom correspondence should be addressed. Phone: +86-
431-5262127. Fax: +86-431-5698041. E-mail: hongjie@ns.ciac.jl.cn.
† Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences.
‡ Graduate School of the Chinese Academy of Sciences.
10.1021/jp044591h CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/08/2005

NIR Luminescent Hybrid Materials
J. Phys. Chem. B, Vol. 109, No. 13, 2005 6175
properties of the Nd3+ ion in the Nd-D-P gel are discussed
The pure gel was synthesized as follows. The molar ratio of
tetraethoxysilane (TEOS)/ethanol/deionized water (acidified with
HCl) in the starting solution was 1:4:4. The resulting clear sol
with a pH value of about 2.5 was stirred for 2 h at RT to ensure
homogeneous mixing and complete hydrolysis, and then placed
in a sealed plastic container. The precursor solution converted
to wet gel after several days of gelation at 40 °C and then was
continuously dried to obtain a transparent monolithic gel.
2.4. Equipment and Measurements. All measurements were
performed at RT. The elemental analyses of carbon, hydrogen,
and nitrogen were carried out on a VarioEL analyzer. FT-IR
spectra were measured within a 4000-400 cm-1 region on a
Bio-Rad model FTS135 infrared spectrophotometer with the
KBr pellet technique. The DR measurements were performed
on a Hitachi U-4100 spectrophotometer. The UV-vis absorption
spectra of DBM and phen were taken with a TU-1901
spectrophotometer using an ethanol solvent. The fluorescence
spectra were recorded on an Edinburgh Analytical Instruments
FLS920 equipped with the laser diode (LD) from the PicoQuant
Company as the light source. The experimental lifetime was
measured with a TR550 (J-Y Company) upon excitation with
a Nd:YAG laser. The sample gel with a diameter of 5.30 mm
and a thickness of 8.92 mm was applied to the optical absorption
measurement. The spectral optical density OD(λ) ) 0.4343lFσ-
(λ) of Nd-D-P gel was recorded at room temperature using a
Shimadzu UV-3101 PC, where l is the thickness of the Nd-
D-P gel, F is the concentration of the Nd3+ ion in the Nd-
D-P gel, and σ(λ) is the absorption cross section. The
corresponding concentration is 7.3 × 1019 Nd/cm3.
using the theory developed by Judd and Ofelt.14
2. Experimental Section
2.1. Synthesis of the Ln(DBM)3phen (Ln ) Nd, Yb)
Complex. The Ln(DBM)3phen complex was prepared according
to the following process. Lanthanide chloride was obtained by
dissolution of Ln2O3 in hydrochloric acid. DBM and phen in a
stoichiometric molar ratio were dissolved in a suitable volume
of anhydrous ethanol. Then, an appropriate amount of 1 M
sodium hydroxide solution was added dropwise to the solution
to adjust the pH value to approximately 7. A stoichiometric
amount of lanthanide chloride ethanol solution was then added
dropwise to the solution under stirring. The molar ratio of Ln3+
/
DBM/phen was 1:3:1. The precipitates were collected after
filtration and dried at 70 °C under vacuum overnight. The
lanthanide complex was recrystallized from an ethanol/acetone
mixture. A blue single crystal for Nd(DBM)3phen‚0.5(C2H5-
OH) and a yellow single crystal for Yb(DBM)3phen were
obtained by slow evaporation from the mixed mother liquor at
room temperature (RT), respectively.
Elemental Analysis. For Nd(DBM)3phen‚0.5(C2H5OH), cal-
culated: C, 68.48%; H, 4.36%; N, 2.75%. Found: C, 68.44%;
H, 4.46%; N, 2.80%. For Yb(DBM)3phen, calculated: C,
66.92%; H, 4.04%; N, 2.74%. Found: C, 66.98%; H, 4.12%;
N, 2.79%.
2.2. Single-Crystal X-ray Diffraction Study. X-ray data for
the selected crystal mounted on a glass fiber were collected on
a CCD area detector with graphite-monochromated Mo KR
radiation. Reflections were collected with a Bruker SMART
APEX detector and processed with SAINT from Bruker. Data
were corrected for Lorentz and polarization effects. The structure
was solved by direct methods and expanded using Fourier
techniques. For Nd(DBM)3phen‚0.5(C2H5OH), the non-hydro-
gen atoms except O(7), C(58), and C(59) were refined aniso-
tropically. Hydrogen atoms on the ethanol of Nd(DBM)3phen‚
0.5(C2H5OH) were not included, and other hydrogen atoms of
Nd(DBM)3phen‚0.5(C2H5OH) and Yb(DBM)3phen were in-
cluded using a riding model. All calculations were performed
using the Bruker SHELXTL crystallographic software package.
Data for the two complexes have been deposited at the
Cambridge Crystallographic Database Center.15a
3. Results and Discussion
3.1. Crystal Structures of Nd(DBM)3phen‚0.5(C2H5OH)
and Yb(DBM)3phen Complexes. The crystal structure of Nd-
(DBM)3phen‚0.5(C2H5OH) with the numbering scheme is
displayed in Figure 1a. Important experimental parameters for
the structure determinations are tabulated in Table 1. The central
Nd3+ ion is coordinated by six oxygen atoms from three DBM
ligands and two nitrogen atoms from the phen ligand. Thus,
the Nd3+ ion exhibits a coordination number of eight. The
coordination geometry of the central Nd3+ ion may be described
as a square antiprism from the coordination site angles (shown
in Figure 1b). Crystallization of Yb(DBM)3phen (Figure 2a,
Table 1) is of a similar manner. The coordination number of
the central Yb3+ ion is also eight, yet the polyhedron can be
regarded as a dodecahedron (shown in Figure 2b). In the
â-diketone rings of two lanthanide complexes, all of the average
distances for the carbon-carbon and carbon-oxygen bonds are
between the single bond distance and the double bond distance.
This can be explained by the fact that there exists conjugated
structure between the phenyl ring and the coordinated â-dike-
tonate, which leads to the delocalization of electron density of
the coordinated â-diketonate chelate ring. Also, the â-diketonate
chelate ring itself is a conjugated structure due to the delocal-
ization of electron density.15b
3.2. IR and DR Spectra. The FT-IR spectra of the Nd-
(DBM)3phen and Yb(DBM)3phen complexes, the Nd-D-P and
Yb-D-P gels, and the pure gel are shown in Figure 3. For the
Nd(DBM)3phen complex (Figure 3A), both the coordination
bonds of Nd-phen and Nd-DBM are evident by the bands
appearingin the range of 400-438 cm-1, corresponding to the
νNd-O vibration and the peak at 511 cm-1 due to the νNd-N
vibration.16,17 With respect to the IR spectrum of the Nd-D-P
gel in Figure 3B, the peak at 1077 cm-1 can be attributed to
the Si-O-Si symmetric stretching vibration, and the band at
2.3. In situ synthesis of a Lanthanide complex via a Sol-
Gel Process (Ln-D-P gel, Ln ) Nd, Yb). The molar ratio
of tetraethoxysilane (TEOS)/ethanol/deionized water (acidified
with HCl) in starting solution was 1:4:4. The resulting clear
sol with a pH value of about 2.5 was stirred for 2 h. Then,
DBM, phen, and LnCl3 ethanol solution were introduced into
the starting solution consecutively. The molar ratio of Ln3+
/
DBM/phen was 1:3:1, and the concentration of the Ln3+ ion is
Ln3+/Si ) 1 mol %. The mixed solution was stirred for several
hours at RT to ensure homogeneous mixing and complete
hydrolysis, and then placed in a sealed plastic container. The
precursor solution converted to wet gel after several days of
gelation at 40 °C and then was continuously dried to obtain a
transparent monolithic gel. The lanthanide complexes were
supposed to be in situ synthesized during the corresponding sol
to monolithic xerogel conversion accompanied with the evapo-
ration of HCl, respectively.
The synthesis of the singly Ln3+-ion-doped silica gel (Ln gel;
Ln ) Nd3+, Yb3+) is similar to that of the Ln-D-P gel except
that the LnCl3 ethanol solution was introduced into the starting
solution instead of DBM, phen, and LnCl3 ethanol solution. And
the concentration of the Ln3+ ion is also Ln3+/Si ) 1 mol %.

6176 J. Phys. Chem. B, Vol. 109, No. 13, 2005
Sun et al.
TABLE 1: Crystal Data and Structure Refinement for
Nd(DBM)3phen‚0.5(C2H5OH) and Yb(DBM)3phen
empirical formula
formula weight
temperature (K)
wavelength (Å)
crystal system
space group
a (Å)
C58H44N2NdO6.50
1017.19
C57H41N2O6Yb
1022.96
293(2)
0.71073
monoclinic
P21/n
15.5804(16)
17.0282(17)
17.6621(18)
90
91.779(2)
90
293(2)
0.71073
triclinic
P1h
12.5701(8)
13.0988(8)
16.2767(10)
93.1700(10)
96.4480(10)
109.3870(10)
2499.8(3), 2
1.351
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3), Z
4683.6(8), 4
1.451
2.051
2060
D
calc (Mg/m3)
absorption coefficient (mm-1) 1.092
F(000)
1036
crystal size (mm)
θ range (deg)
limiting indices
0.21 × 0.18 × 0.09 0.25 × 0.17 × 0.09
1.73 to 26.02
-15 e h e 12,
-13 e k e16,
-20 e l e19
14 101
1.66 to 26.18
-19 e h e 19,
-21 e k e 17,
y-19 e l e 21
26 141
reflections collected
independent reflections
max. and min. transmission
refinement method
9582 (Rint ) 0.0296) 9294 (Rint ) 0.0248)
0.9081 and 0.8032 0.8369 and 0.6281
full-matrix
full-matrix
least squares on F2 least squares on F2
data/restraints/parameters
goodness-of-fit on F2
9582/2/607
9294/0/595
1.069
1.033
final R indices (I > 2σ(I))
R1 ) 0.0601,
wR2 ) 0.1452
R1 ) 0.0791,
wR2 ) 0.1580
1.424 and -0.422
R1 ) 0.0330,
wR2 ) 0.0734
R1 ) 0.0454,
wR2 ) 0.0798
0.936 and -0.302
R indices (all data)
largest difference
peak and hole (e Å-3
)
excited level (π*) S1 of the organic ligands. In curves A and B,
the characteristic absorption bands due to the transition from
the ground state to the excited states of the Nd3+ ions are both
observed, where the peaks at 514, 527, 581, 675, 747, 802, and
4
2
4
2
4
875 nm are assigned to I9/2 f G11/2, I9/2 f G9/2, I9/2
f
,
2G7/2, 4I9/2 f 4F9/2, 4I9/2 f 4F7/2, 4I9/2 f 4F5/2, and 4I9/2 f 4F3/2
respectively.20 This, together with the appearance of similar
absorption of ligands in both curves, suggests that the neody-
mium complex is in situ synthesized in the Nd-D-P gel.
Similarly, in the DR spectra of the Yb(DBM)3phen complex
and the Yb-D-P gel (Figure 5), the broad ligands absorption
bands (200-400 nm) and the characteristic absorption band of
the Yb3+ ion at 975 nm (2F9/2 f 2F5/2) are both observed, which
also suggests that the ytterbium complex is in situ synthesized
in the Yb-D-P gel.
3.3. Antenna Fluorescence. The excitation spectra of Ln-
(DBM)3phen complexes (Ln ) Nd, Yb; monitored at 1060 nm
for the Nd(DBM)3phen complex and 980 nm for the Yb-
(DBM)3phen complex) and the absorption spectra of the ligands
(DBM and phen) are shown in Figure 6. As is clearly visible in
Figure 6, there are overlaps between the excitation band of the
lanthanide complexes and the absorption bands of DBM and
phen, which indicates the typical sensitization of the Ln3+ ions
by the two organic ligands, an antenna effect,9 and thus confirms
that the Ln3+ ions are surrounded by DBM and phen in the
lanthanide complexes.21 It is also worth noting that the overlap
between the absorption of DBM and the lanthanide excitation
bands is larger than that between the absorption of phen and
the excitation bands, which suggests that the antenna effect of
DBM is more efficient than that of phen. Thus, we can come
to the conclusion that the intramolecular energy transfer in the
Ln(DBM)3phen complex mainly occurs between the DBM
ligand and the Ln3+ ions.15b
Figure 1. (a) ORTEP plot for Nd(DBM)3phen‚0.5(C2H5OH) with
ellipsoids drawn at the 30% probability level. Hydrogen atoms and
ethanol were omitted for clarity. (b) Coordination polyhedron of the
neodymium (III) ion.
452 cm-1 corresponds to the bending vibration of the O-Si-O
band.18 It is worth noting that the stretching vibration frequency
of CdN of phen in the Nd-D-P gel has red-shifted to 1620
cm-1 compared to pure phen, which can suggest the possible
coordination of Nd-N. In comparison to the region 400-457
cm-1 of Figure 3E (see inset), in Figure 3B a new absorption
band appears at 417 cm-1 (see inset) that can be assigned to
the stretching band of Nd-O,17,19 even though it is not
prominent. This is probably due to the low concentration of
Nd3+ ions in the Nd-D-P gel matrix (Ln3+/Si ) 1 mol %).
For Yb(DBM)3phen and Yb-D-P gel (Figures 3C and 3D),
the IR spectra are similar to those of Nd(DBM)3phen and Nd-
D-P gel, respectively. Therefore, the possible in situ syntheses
of lanthanide complexes in the corresponding Ln-D-P gels
(Ln ) Nd, Yb) can be suggested.
The DR spectra of the Nd(DBM)3phen complex, Nd-D-P
gel, and Nd gel are shown in Figure 4. The band at 1180 nm,
which is not shown in the DR spectrum of the Nd(DBM)3phen
complex but shown in the DR spectra of the Nd-D-P gel and
the Nd gel, may be assigned to the absorption of the silica gel.
In comparison to the DR spectrum of the Nd gel (Figure 4C),
in the UV region of curves A and B (200-400 nm) broad
absorption bands are both observed and can be attributed to
electronic transitions from the ground-state level (π) S0 to the
In the excitation spectrum of the Nd(DBM)3phen complex
(Figure 6), a broad band ranging from 230 to 490 nm due to
the absorption of the organic ligands superimposed with some

NIR Luminescent Hybrid Materials
J. Phys. Chem. B, Vol. 109, No. 13, 2005 6177
Figure 4. DR spectra of the (A) Nd(DBM)3phen complex, (B) Nd-
D-P gel, and (C) Nd gel.
Figure 2. (a) ORTEP plot for Yb(DBM)3phen with ellipsoids drawn
at the 30% probability level. Hydrogen atoms were omitted for clarity.
(b) Coordination polyhedron of the ytterbium (III) ion.
Figure 5. DR spectra of the (A) Yb(DBM)3phen complex and (B)
Yb-D-P gel.
Figure 3. FT-IR spectra of the (A) Nd(DBM)3phen complex, (B) Nd-
D-P gel, (C) Yb(DBM)3phen complex, (D) Yb-D-P gel, and (E)
pure gel. The inset shows the 400-457 cm-1 range of curves B and E.
Figure 6. Excitation spectra of Nd(DBM)3phen (λem ) 1060 nm) and
Yb(DBM)3phen (λem ) 980 nm) and UV-vis absorption spectra of
DBM and phen.
excitation bands originating from the characteristic absorption
transition of the Nd3+ ion is observed. These f-f transitions
4
2
4
2
which proves that luminescence sensitization via excitation of
ligands is much more efficient than direct excitation of the
absorption levels of the Nd3+ ions. For the excitation spectrum
of the Nd-D-P gel (λem ) 1064 nm), a similar absorption of
correspond to I9/2 f G11/2 (513 nm) and I9/2 f G9/2 (527
nm) of the Nd3+ ion, which are in agreement with those of the
DR spectrum (Figure 4A). It is worth noting that these
absorption transitions are weaker than those of the ligands,

6178 J. Phys. Chem. B, Vol. 109, No. 13, 2005
Sun et al.
Figure 9. Emission spectra of the Yb(DBM)3phen complex and Yb-
D-P gel (λex ) 397 nm).
Figure 7. Emission spectra of the Nd(DBM)3phen complex and Nd-
D-P gel (λex ) 397 nm).
results verify that the neodymium complex is in situ synthesized
in the Nd-D-P gel, which is in accord with the preliminary
conclusion obtained from the IR and DR spectra.
The excitation spectra of the Yb(DBM)3phen complex (Figure
6) and the Yb-D-P gel (Figure 8) were obtained by monitoring
the characteristic emission of the Yb3+ ions at 980 nm. The
excitation spectra are dominated by a broad band ranging from
225 to 500 nm for the Yb(DBM)3phen complex and a broad
band from 260 to 466 nm for the Yb-D-P gel. These two
broad bands can be assigned to the absorption of the organic
ligands and are agreement with those in the DR spectra (Figure
5).
The emission spectra of the Yb(DBM)3phen complex and the
Yb-D-P gel (Figure 9) were obtained by direct excitation of
the ligands (λex ) 397 nm). The emission spectrum of the Yb-
D-P gel is similar to that of the Yb(DBM)3phen complex. In
both curves, the prominent 980 nm emission band can be
2
2
observed, which is assigned to the F5/2 f F7/2 transition of
the Yb3+ ion. It should be noted that the Yb3+ ion emission
band is not a single sharp transition but an envelope of bands
arising at lower and higher energies than the primary 980 nm
band. Similar splitting has been reported previously,22a,23 and
in early spectroscopic studies on ytterbium â-diketone com-
pounds it was suggested that crystal field splitting is the origin
of the structure in the emission spectra.24 As discussed for the
Nd-D-P gel above, to verify that the ytterbium complex was
in situ synthesized in the Yb-D-P gel, a singly Yb3+-ion-doped
silica gel (Yb gel) was also prepared with the same Yb/Si molar
ratio. In the corresponding emission spectrum (not shown), by
excitation at 397 nm no characteristic peak of the Yb3+ ion could
be detected in our experimental conditions, which indicates that
in the Yb-D-P gel the Yb3+ ion emission does come from
the contribution of the energy transfer from the organic ligands.
This confirms that the ytterbium complex is also in situ
synthesized in the Yb-D-P gel, which is in agreement with
the conclusion obtained from the IR and DR spectra.
Figure 8. Excitation spectra of the Nd-D-P gel (λem ) 1064 nm)
and Yb-D-P gel (λem ) 980 nm).
organic ligands ranging from 250 to 450 nm (Figure 8) is
observed compared to that of the Nd(DBM)3phen complex.
The emission spectra of the Nd(DBM)3phen complex and the
Nd-D-P gel (Figure 7) were obtained upon excitation of the
ligands (λex ) 397 nm). In the two curves, the luminescence
spectra of NdIII both consist of three bands at λ ) 880, 1060,
and 1340 nm, which are attributed to the f-f transitions of 4F3/2
4
4
(emitting level) f I9/2, f f ,
4F3/2 4I11/2, and F3/2 4I13/2
respectively. The strongest emission is observed at 1060 nm,
whereas the emissions at 880 and 1340 nm are weaker. The
profiles of the emission bands and the relative intensity of the
Nd3+ luminescence for the Nd(DBM)3phen complex and the
Nd-D-P gel are in agreement with previously reported spectra
of organic neodymium complexes.10,22 To verify that the
neodymium complex was in situ synthesized in the Nd-D-P
gel, a singly Nd3+-ion-doped silica gel (Nd gel) was prepared
using the same Nd/Si molar ratio. In the corresponding emission
spectrum (not shown), no characteristic peaks of the Nd3+ ion
could be detected by excitation at 397 nm in our experimental
conditions. The result indicates that in the Nd-D-P gel the
obtained characteristic luminescence of the Nd3+ ion irradiated
at 397 nm is undoubtedly attributable to the contribution of the
intramolecular energy transfer from the organic ligands, since
the Nd3+ ion has no absorption at this wavelength. All of these
3.4. Energy Transfer Mechanism. Direct excitation is very
demanding because the optical transitions within the 4f subshells
of lanthanide ions are parity forbidden. The indirect excitation
by energy transfer from an organic antenna chromophore not
only circumvents this excitation problem but also allows
excitation at wavelengths where the lanthanide ion does not
display a significant absorption. To obtain an excellent lumi-
nescent material, one has to take advantage of the strong

NIR Luminescent Hybrid Materials
J. Phys. Chem. B, Vol. 109, No. 13, 2005 6179
SCHEME 1: Model for the Main Pathways in the
Sensitization Process (Left) and Energy Diagram of the
4f Levels of the Nd3+ and Yb3+ Ions (Right)
scheme (the right of Scheme 1), consisting of only two levels,
2
2
the F7/2 ground state and the F5/2 excited state. There is no
excited-state absorption upon reducing the effective laser cross
section, no up-conversion, no concentration quenching, and no
absorption in the visible range.27 As discussed above, the
2
obtained characteristic band at 980 nm is assigned to the F5/2
f
2F7/2 transition of the Yb3+ ion in the Yb(DBM)3phen
complex and the Yb-D-P gel (Figure 9), which is also very
important for laser emission.
Lanthanides that emit at longer wavelengths have relatively
small energy gaps between the excited and the ground state.
This allows the use of antenna with much lower triplet state
energies.4a For energy transfer to occur efficiently, there should
be spectral overlap between the donor (ligand) and the acceptor
(Ln3+ ion) states. According to Dexter’s theory,28 the suitability
of the energy difference between the resonance level of the Ln3+
ion and the triplet state of the ligand is a critical factor for
efficient energy transfer. If the energy difference is too big, then
the energy transfer rate constant will decrease due to the
diminution in the overlap between the donor and the acceptor.
On the contrary, if the energy difference is too small, then the
energy back-transfer can occur from the Ln3+ ion to the
resonance level of the triplet state of the ligand. The energy
gap must be at least 10kBT, (2000 cm-1) to effectively preclude
energy back-transfer.29 DBM, whose triplet state is 20 400
cm-1 30 can match well with the 4f levels of the Nd3+ and Yb3+
,
absorbing capacity of organic ligands and the possibility of
transferring the excitation energy from the triplet states of the
ligands to the lanthanide ions. As described above, we obtained
the characteristic Ln3+ ion emission upon excitation at the
absorption of the organic ligands in both Ln(DBM)3phen
complexes and Ln-D-P gels. This indicates that (1) ligands
(DBM and phen) are able to transfer the absorbed energy to
the central metal Ln3+ ions, an antenna effect, which is in
agreement with the excitation results mentioned above (Figure
6) and (2) complexes are formed between the Ln3+ ions and
the ligands. The near-infrared luminescence obtained in this
study shows that the ligands shield the lanthanide ions well from
their surroundings and efficiently transfer energy from their
triplet states to the Ln3+ ions. Thus, a model for the indirect
excitation mechanism is suggested and shown as a schematic
energy diagram in Scheme 1. From the scheme, it can be seen
that the electrons of the ligands of the lanthanide complex are
excited from the singlet S0 ground state to the singlet S1 excited
state by absorbing the energy. The energy of the S1 excited state
is then transferred to the triplet excited state of the ligands
through intersystem crossing. And subsequently the excitation
energy is transferred to the 4f states of the Ln3+ ions, ultimately
resulting in sensitized Ln3+ ion emission.25
ions. In the meantime, using the â-diketonate as a ligand for
neodymium and ytterbium in the matrix has several advantages.
First, the ligand protects the Ln3+ ions (Ln ) Nd, Yb) from the
residual water molecules and silanol groups in the sol-gel
matrix, which decreases the quenching effect due to the high
energy vibration of the water molecules. Second, the diketonate
ligand has a long wavelength absorption for its π-π* transition
and consequently has been targeted for its ability to sensitize
the luminescence of the Ln3+ ions at relatively long wavelengths.
Third, since the coordination ability of oxygen with the
lanthanide ions is stronger than that of nitrogen, in the absence
of â-diketonate, the phen ligand cannot successfully compete
with the water molecules for a place in the first coordination
sphere around the lanthanide ions.31 Phen, which is widely used
as the second ligand in the complexes, was introduced in our
lanthanide complexes to better sensitize Ln3+ ion luminescence
by replacing the H2O groups that can quench the luminescence
of the Ln3+ ions and optimizing the emission intensity of the
Ln3+ ions. The combination of both ligands has essentially
complementary absorption spectra in the UV region and
effectively sensitizes over a wide wavelength range followed
by transferring the energy to the central Ln3+ ions.
A detailed scheme of the 4f energy levels of the Nd3+ and
Yb3+ ions is depicted on the right of Scheme 1. As discussed
above, for the Nd(DBM)3phen complex and the Nd-D-P gel
(Figure 7), the emission bands at 880, 1060, and 1340 nm
correspond to the 4F3/2 f 4I9/2, 4F3/2 f 4I11/2, and 4F3/2 f 4I13/2
transitions, respectively. That is to say that through intramo-
lecular energy transfer process the excitation energy is trans-
ferred from the ligands to the 4f levels of the Nd3+ ion. And
from the upper 4f levels, the relaxation to the 4F3/2 first excited
state of Nd3+ can take place, and finally the Nd3+ ion may decay
to the 4I9/2, 4I11/2, and 4I13/2 states by the emissions of 880, 1060,
and 1340 nm, respectively. Among the three emission bands,
the band at 1060 nm is the most important because it is
potentially applicable for laser emission.26 For the Yb(DBM)3-
phen complex and the Yb-D-P gel, the Yb3+ ion has some
advantages for laser emission due to its very simple energy level
3.5. Judd-Ofelt Analysis. It is known that the Judd-Ofelt
theory14 is one of the most successful theories in estimating
the magnitude of the forced electric dipole transitions of rare
earth ions. As discussed above, the Nd-D-P gel has the
potential for development in laser applications. To further
evaluate the potential of rare-earth-doped materials, it is essential
to study the radiative properties of the rare earth organic
complexes. As usual, the radiative properties of trivalent rare
earth ions in host matrix can be predicted from optical absorption
measurements and by using the Judd-Ofelt theory.
According to the Judd-Ofelt theory, the data of the absorp-
tion spectrum can be used to predict the radiative lifetime of
the Nd3+ ion 4F3/2 excited J manifold and the branching rations
4
of the fluorescence transitions to the lower-lying IJ manifold.
The procedure involves first measuring the line oscillator
4
strength Sexp of the transitions between the ground I9/2
J

6180 J. Phys. Chem. B, Vol. 109, No. 13, 2005
Sun et al.
4f3 configuration of the Nd3+ ion. They may be regarded as
phenomenological parameters that characterize the radiative
transition probabilities within the ground configuration. Through
the use of eq 1, the experimental oscillator strength Sexp for the
electric dipole transition can be obtained. Then, the parameters
Ωt can be derived by a least-squares fitting of eq 2: Ω2 ) 76.23
× 10-20 cm2, Ω4 ) 4.778 × 10-20 cm2, Ω6 ) 3.064 × 10-20
cm2.
The interpretation of the physical meaning of the phenom-
enological oscillator strength parameters still remains a con-
troversial matter for discussion. Ω2 is usually related to the
degree of covalency in the lanthanide-first coordination shell
interaction.33b,38 In the sense of the dynamic coupling contribu-
tion to the total intensity,38c the polarization of the ligand field
induces stronger lanthanide-ligand bonds and an increase in
electric dipolar transitions for noncentrosymmetric ligand fields.
The large value for Ω2 in this title indicates the presence of
covalent bonding between the Nd3+ ion and the surrounding
ligands, as is reasonable.35
Figure 10. Absorption spectrum of the Nd-D-P gel.
TABLE 2: Measured and Calculated Line Strengths of the
Nd3+ Ion in the Nd-D-P Gela
The values of the parameters are then used to recalculate the
transition line strengths of the absorption bands using eq 2. The
calculated line strengths Scal of the five absorption bands are
tabulated in Table 2. To justify the results obtained, a measure
of the accuracy of the fit is given by the root-mean-square (rms)
deviation of the experimental and calculated line strengths,
which is obtained by
level
λ (nm)
Sexp (× 10-20 cm2)
Scal (× 10-20 cm2)
2G7/2
2H11/2
4F9/2
4S3/2
4F7/2
4F5/2
581
624
681.5
742.6
6.7508
0.0680
0.1607
2.3157
6.7500
0.0524
0.2403
2.3119
799.1
2.4270
2.4254
4
a All transitions are from the I9/2 state.
1/2
(Smea - Scal)2
rms∆S )
(3)
[
]
manifold and the excited J manifolds of the Nd3+ ion. Figure
10 shows the absorption spectrum of the Nd-D-P gel. Five
Nd3+ ion absorption bands in the absorption spectrum were
selected to determine the phenomenological oscillator strength
parameters. The band positions along with the assignments in
the absorption spectrum are shown in Table 2. The measured
line strength Smea can be determined using the following
expression32
N - M
where N is the number of spectral bands analyzed and M is the
number of parameters determined. In this case, M ) 3. The
values in Table 2 provide an rms deviation of 0.0574 × 10-20
cm2, which indicates that the result derived by a least-squares
fitting of eq 2 is good.
From the parameters Ωt obtained above, the radiative transi-
tion rates for electric dipole transitions from the initial J′
manifold |(S′,L′)J′ to the terminal manifold |(Sh,Lh)Jh can be
calculated using the following expression30
(n2 + 2)2
8π3e2λh
3ch(2J + 1)
1
n
σ(λ) dλ )
S exp
(1)
∫
[
]
9
where σ(λ) is the absorption cross section at wavelength λ, λh is
the mean wavelength of the specific absorption band, e, h, and
c are the electron charge, Planck’s constant, and the velocity of
light, respectively. J is the total angular momentum quantum
number of the initial level (for Nd3+ ion J ) 9/2). And an average
index of refraction of 1.5 was used.33
n(n2 + 2)2
64π4e2
A[4F3/2;(Sh,Lh)Jh] )
×
3h(2J′ + 1)λh3
9
Ωt| F3/2|U(t)|(Sh,Lh)Jh | (4)
4
2
∑
t)2,4,6
According to Judd-Ofelt theory,14 the experimental oscillator
strength of an electric dipole transition between an initial J
manifold |(S,L)J and a terminal J′ manifold |(S′,L′)J′ can be
expressed as the form34
where (Sh,Lh)Jh are quantum numbers of the lower states, J′) 3/2,
and λh is the mean wavelength of the emission transition (Figure
7). And the related reduced matrix elements of the emissive
transitions are given in ref 39 for the Nd3+ ion.
2
Ωt| (S,L)J|U(t)|(S′,L′)J′ |
(2)
The radiative lifetime represents an effective average over
site-to-site variations in the local Nd3+ environment. The
radiative lifetime (τrad) and the total radiative transition rate are
related by the expression40
S )
∑
t)2,4,6
where |U(t)| are the doubly reduced matrix elements corre-
sponding to the J-J′ transition. The matrix elements depend
only on the angular momentum of the Nd3+ ion states and are
essentially independent of the ion environment.35 In our work,
the calculated values of the square of the reduced matrix
elements are cited from Carnall’s data.36 When two or more
absorption manifolds overlapped, the matrix element was taken
to be the sum of the corresponding squared matrix elements.37
The Ωt (t ) 2, 4, 6), the oscillator strength parameters, are
independent of electronic quantum numbers with the ground
1
τrad
)
(5)
A[(S′,L′)J′;(Sh,Lh)Jh]
∑
Sh,Lh,Jh
And the fluorescence branching ratios can be determined from
the radiative decay rates by

NIR Luminescent Hybrid Materials
A[(S′,L′)J′;(Sh,Lh)Jh]
J. Phys. Chem. B, Vol. 109, No. 13, 2005 6181
4
4
TABLE 3: Spectra Parameters for the F3/2 f IJ Transition
of the Nd3+ Ion in the Nd-D-P Gel
â[(S′,L′)J′;(Sh,Lh)Jh] )
(6)
4F3/2 f (S′,L′)J′ λ (nm) Scal (× 10-20 cm2) A (s-1
)
âc σe (× 10-20 cm2)
A[(S′,L′)J′;(Sh,Lh)Jh]
∑
4F3/2 f 4I9/2
881
1.263
1.800
0.639
969.1 0.507
802.4 0.420
140.8 0.073
0.511
1.414
0.320
Sh,Lh,Jh
4F3/2 f 4I11/2 1064
4F3/2 f 4I13/2 1349
4
τrad (µs)
523
The radiative lifetime of the F3/2 state has been calculated
to be 523 µs, which is an important parameter in consideration
of the pumping requirement for the threshold of laser action.41
D-P gel can be considered as a possible candidate for a solid-
state laser transition.
4
The experimental lifetime of the F3/2 state was measured.
Analysis of the monoexponential decay results in a lifetime of
54 µs, which is lower than the radiative lifetime calculated from
the theory. This is due to the effect of the radiationless relaxation
process, which results in the difference between the experimental
lifetime and the calculated result. Work on decreasing the effect
of the radiationless relaxation is in process. The fluorescence
branching ratio is a critical parameter to the laser designer,
because it characterizes the possibility of attaining stimulated
emission from any specific transition.42
Acknowledgment. This work was supported by the National
Natural Science Foundation of China (Grant Nos. 20171043
and 20372060), the Key National Natural Science Foun-
dation of China (Grant No. 20131010), the National Natural
Science Foundation of ChinasSpecial for Instruments (Grant
No. 20121701), the “863” National Foundation for High
Technology Development and Programming (Grant No.
2002AA302105_2002AA324080), and the Foreign Communion
& Cooperation of the National Natural Science Foundation of
China (Grant No. 20340420326). We are grateful to Professor
Jiang-Gao Mao of the Fujian Institute of Research on the
Structure of Matter, Chinese Academy of Sciences for assistance
with the fluorescence measurements. We also thank Professors
Si-Yuan Zhang and Zhi-Jian Wu of the Changchun Institute of
Applied Chemistry guidance with the Judd-Ofelt theory.
With the value for the radiative transition rate calculated
above and the corresponding emission spectrum, for a Lorentz
line the stimulated emission cross section σe is calculated by
Aλ2
4π2n2∆ν
σe )
(7)
where ∆ν is the frequency full width at half-maximum and λ is
the wavelength of the emission peak. The values of the radiative
transition rates A, the fluorescence branching ratios â, the
radiative lifetime τrad, and the emission cross section σe are
presented in Table 3.
Supporting Information Available: Crystallographic in-
formation for Nd(DBM)3phen‚0.5(C2H5OH) and Yb(DBM)3phen.
This material is available free of charge via the Internet at
http://pubs.acs.org.
It can be shown that the radiative lifetime of the transition
involved is comparable with the radiative lifetimes of neody-
mium laser glasses.43 The emission cross section σe of the 4F3/2
References and Notes
(1) Sabbatini, N.; Guardigli, M.; Lehn, J.-M. Coord. Chem. ReV. 1993,
123, 201.
(2) (a) Parker, D.; Williams, J. A. G. J. Chem. Soc., Dalton Trans.
1996, 3613. (b) Elbanowski, M.; Makowska, B. J. Photochem. Photobiol.,
A 1996, 99, 85. (c) Sabbatini, N.; Guardigli, M.; Manet, I. AdV. Photochem.
1997, 23, 213.
(3) (a) Beeby, A.; Faulkner, S. Chem. Phys. Lett., 1997, 266, 116. (b)
Imbert, D.; Cantuel, M.; Bu¨nzli, J. C. G.; Bernardinelli, G.; Piguet, C. J.
Am. Chem. Soc. 2003, 125, 15698.
4
f I11/2 fluorescence transition of the Nd3+ ion is one of the
most important parameters for laser design, and it is dependent
only on Ω4 and Ω6, because of the triangle rule |J - J′| e λ e
(J + J′), |U(t)|2 ) 0 (t ) 2).39 In our case, the stimulated
emission cross section of the 4F3/2 f 4I11/2 fluorescence transition
of the Nd3+ ion in the Nd-D-P gel is 1.414 × 10-20 cm2,
(4) (a) Beeby, A.; Dickins, R. S.; Faulkner, S.; Parker, D.; Williams,
J. A. G. Chem. Commun. 1997, 1401. (b) Horrocks, W. D., Jr.; Bolender,
J. P.; Smith, W. D.; Supkowski, R. M. J. Am. Chem. Soc. 1997, 119, 5972.
(c) Kang, T. S.; Harrison, B. S.; Bouguettaya, M.; Foley, T. J.; Boncella,
J. M.; Schanze, K. S.; Reynolds, J. R. AdV. Funct. Mater. 2003, 13, 205.
(5) (a) Weber, M. J. In Lanthanide and Actinide Chemistry and
Spectroscopy; Edelstein, N. M., Ed.; ACS Symposium Series 131; American
Chemical Society: Washington, DC, 1980, p 275. (b) Ryo, M.; Wada, Y.;
Okubo, T.; Hasegawa, Y.; Yanagida, S. J. Phys. Chem. B 2003, 107, 11302.
(6) Davies, G. M.; Aarons, R. J.; Motson, G. R.; Jeffery, J. C.; Adams,
H.; Faulkner, S.; Ward, M. D. J. Chem. Soc., Dalton Trans. 2004, 1136.
(7) Weissman, S. I. J. Chem. Phys. 1942, 10, 214.
(8) (a) Melby, L. R.; Rose, N. J.; Abramson, E.; Caris, J. C. J. Am.
Chem. Soc. 1964, 86, 5117. (b) Binnemans, K.; Lenaerts, P.; Driesen, K.;
Go¨rller-Walrand, C. J. Mater. Chem. 2004, 14, 191. (c) Carlos, L. D.; Sa´
Ferreira, R. A.; Rainho, J. P.; de Zea Bermudez, V. AdV. Funct. Mater.
2002, 12, 819.
(9) (a) Bekiari, V.; Lianos, P. AdV. Mater. 1998, 10, 1455. (b) Sabbatini,
N.; Mecati, A.; Guardigli, M.; Balazani, V.; Lehn, J. M.; Zeissel, R.; Ungaro,
R. J. Lumin. 1991, 48-49, 463. (c) Sabbatini, N.; Guardigli, M.; Lehn, J.
M. Coord. Chem. ReV. 1993, 123, 201. (d) Driesen, K.; Deun, R. V.; Go¨rller-
Walrand, C.; Binnemans, K. Chem. Mater. 2004, 16, 1531.
(10) Klink, S. I.; Grave, L.; Reinhoudt, D. N.; van Veggel, F. C. J. M.;
Werts, M. H. V.; Geurts, F. A. J.; Hofstraat, J. W. J. Phys. Chem. A 2000,
104, 5457.
(11) (a) Sanchez, C.; Soler-Illia, G. J. A. A.; Ribot, F.; Lalot, T.; Mayer,
C. R.; Cabuil, V. Chem. Mater. 2001, 13, 3061. (b) Corriu, R. J. P.; Embert,
F.; Guari, Y.; Mehdi, A.; Reye´, C. Chem. Commun. 2001, 1116. (c)
Hernandez, R.; Franville, A. C.; Minoofar, P.; Dunn, B.; Zink, J. I. J. Am.
Chem. Soc. 2001, 123, 1248. (d) Li, H. H.; Inoue, S.; Machida, K. I.; Adachi,
G. Y. Chem. Mater. 1999, 11, 3171.
which is comparable with those shown by glasses used in solid-
4
state laser applications.44 All of these showed that the F3/2
f
4I11/2 transition of the Nd3+ ion in the Nd-D-P gel can be
considered as a possible laser transition.
4. Conclusions
We successfully demonstrated the crystal structures of the
Ln(DBM)3phen complexes and the syntheses of transparent
homogeneous hybrid materials containing the corresponding
lanthanide complex by using an in situ synthesis technique. The
properties of the Ln-D-P gel were investigated and compared
with those of the Ln(DBM)3phen complexes. The evidence for
the lanthanide complex in situ synthesized in the corresponding
Ln-D-P gel was mainly obtained from fluorescence properties.
We have demonstrated the NIR luminescence of Ln(DBM)3phen
complexes and Ln-D-P gels upon indirect excitation of them,
mediated by the sensitizing effect of the ligands in the lanthanide
complexes, an antenna effect. According to the Judd-Ofelt
theory, the radiative properties of the Nd3+ ion in the Nd-
D-P gel, such as radiative transition rates, emission cross
sections, fluorescence branching ratios, and radiative lifetime
were calculated and analyzed. On the basis of the experimental
data and Judd-Ofelt analysis, we can come to the conclusion
4
4
that the F3/2 f I11/2 transition of the Nd3+ ion in the Nd-

6182 J. Phys. Chem. B, Vol. 109, No. 13, 2005
Sun et al.
(12) (a) Driesen, K.; Go¨rller-Walrand, C.; Binnemans, K. J. Mater. Sci.
Eng. C 2001, 18, 255. (b) Driesen, K.; Lenaerts, P.; Binnemans, K.; Go¨rller-
Walrand, C. Phys. Chem. Chem. Phys. 2002, 4, 552.
(13) (a) Qian, G. D.; Yang, Z.; Wang, M. Q. J. Lumin. 2002, 96, 211.
(b) Qian, G. D.; Wang, M. Q.; Yang, Z. J. Phys. Chem. Solids 2002, 63,
1829.
(28) Dexter, D. L. J. Chem. Phys. 1953, 21, 836.
(29) Beeby, A.; Faulkner, S.; Parker, D.; Williams, J. A. G. J. Chem.
Soc., Perkin Trans. 2 2001, 1268.
(30) Kim, H. J.; Lee, J. E.; Kim, Y. S.; Park, N. G. Opt. Mater. 2002,
21, 181.
(31) (a) Frey, S. T.; Gong, M. L.; Horrocks, W. D., Jr. Inorg. Chem.
1994, 33, 3229. (b) Frey, S. T.; Horrocks, W. D., Jr. Inorg. Chim. Acta
1995, 229, 383. (c) Malta, O. L.; Batista, H. J.; Carlos, L. D. Chem. Phys.
2002, 282, 21.
(32) (a) Wang, G. F.; Chen, W. Z.; Li, Z. B.; Hu, Z. S. Phys. ReV. B
1999, 60, 15469. (b) Hasegawa, Y.; Yamamuro, M.; Wada, Y.; Kanehisa,
N.; Kai, Y.; Yanagida, S. J. Phys. Chem. A 2003, 107, 1697.
(33) (a) Soares-Santos, P. C. R.; Nogueira, H. I. S.; Fe´lix, V.; Drew,
M. G. B.; Sa´ Ferreira, R. A.; Carlos, L. D.; Trindade, T. Chem. Mater.
2003, 15, 100. (b) Malta, O. L.; Couto dos Santos, M. A.; Thompson, L.
C.; Ito, N. K. J. Lumin. 1996, 69, 77.
(34) (a) Wang, G. F. J. Opt. Soc. Am. B 2001, 18, 173. (b) Zheng, Z.
Q.; Liang, H.; Ming, H.; Zhang, Q. J.; Xie, J. P. Opt. Commun. 2004, 233,
149.
(35) Koeppen, C.; Yamada, S.; Jiang, G.; Garito, A. F. J. Opt. Soc. Am.
B 1997, 14, 155.
(36) Carnall, W. T.; Fields, P. R.; Rajnak, K. J. Chem. Phys. 1968, 49,
4424.
(14) (a) Judd, B. R. Phys. ReV. 1962, 127, 750. (b) Oflet, G. S. J. Chem.
Phys. 1962, 37, 511.
(15) (a) Crystallographic data for the structure reported in this paper
have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-249292 for Nd(DBM)3phen‚0.5(C2H5-
OH) and CCDC-249293 for Yb(DBM)3phen. Copies of the data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html or
on application to The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, U. K.; fax, (+44) 1223 336 033; e-mail, deposit@ccdc.cam.ac.uk.
(b) Yu, J. B.; Zhang, H. J.; Fu, L. S.; Deng, R. P.; Zhou, L.; Li, H. R.; Liu,
F. Y.; Fu, H. L. Inorg. Chem. Commun. 2003, 6, 852.
(16) Bian, L. J.; Xi, H. A.; Qian, X. F.; Yin, J.; Zhu, Z. K.; Lu, Q. H.
Mater. Res. Bull. 2002, 37, 2293.
(17) Li, Y. Y.; Gong, M. L.; Yang, Y. S.; Li, M. Q.; Chen, R. Y. J.
Inorg. Chem. 1990, 6, 249.
(18) Li, H. R.; Zhang, H. J.; Lin, J.; Wang, S. B.; Yang, K. Y. J. Non-
Cryst. Solids 2000, 278, 218.
(19) Holtzclaw, H. F., Jr.; Collman, J. P. J. Am. Chem. Soc. 1957, 79,
3318.
(20) Hasegawa, Y.; Kimura, Y.; Murakoshi, K.; Wada, Y.; Kim, J. H.;
Nakashima, N.; Yamanaka, T.; Yanagida, S. J. Phys. Chem. 1996, 100,
10201.
(37) Mehta, V.; Aka, G.; Dawar, A. L.; Mansingh, A. Opt. Mater. 1999,
12, 53.
(38) (a) Malta, O. L.; Brito, H. F.; Menezes, J. F. S.; Goncalves e Silva,
F. R.; Alves, S., Jr.; Farias, F. S., Jr.; de Andrade, A. V. M. J. Lumin.
1997, 75, 255. (b) Oomen, E. W. J. L.; van Dongen, A. M. A. J. Non-
Cryst. Solids 1989, 111, 205. (c) Judd, B. R. J. Chem. Phys. 1979, 70,
4830.
(21) (a) Li, H. R.; Lin, J.; Zhang, H. J.; Fu, L. S.; Meng, Q. G.; Wang,
S. B. Chem. Mater. 2002, 14, 3651. (b) Kawa, M.; Fre´chet, J. M. J. Chem.
Mater. 1998, 10, 286.
(22) (a) Deun, R. V.; Moors, D.; Fre´, B. D.; Binnemans, K. J. Mater.
Chem. 2003, 13, 1520. (b) Iwamuro, M.; Wada, Y.; Kitamura, T.;
Nakashima, N.; Yanagida, S. Phys. Chem. Chem. Phys. 2000, 2, 2291.
(23) (a) Asano-Someda, M.; Kaizu, Y. J. Photochem. Photobiol., A 2001,
139, 161. (b) Tsvirko, M. P.; Stelmakh, G. F.; Pyatosin, V. E.; Solovyov,
K. N.; Kachura, T. F. Chem. Phys. Lett. 1980, 73, 80.
(24) Perkins, W. G.; Crosby, G. A. J. Chem. Phys. 1965, 42, 407.
(25) Klink, S. I.; Hebbink, G. A.; Grave, L.; van Veggel, F. C. J. M.;
Reinhoudt, D. N.; Slooff, L. H.; Polman, A.; Hofstraat, J. W. J. Appl. Phys.
1999, 86, 1181.
(26) Klink, S. I.; Alink, P. O.; Grave, L.; Peters, F. G. A.; Hofstraat, J.
W.; Geurts, F.; van Veggel, F. C. J. M. J. Chem. Soc., Perkin Trans. 2
2001, 363.
(27) Boulon, G.; Collombet, A.; Brenier, A.; Cohen-Adad, M. T.;
Yoshikawa, A.; Lebbou, K.; Lee, J. H.; Fukuda, T. AdV. Funct. Mater. 2001,
11, 263.
(39) Kaminskii, A. A.; Boulon, G.; Buoncristiani, M.; Di Bartolo,
B.; Kornienko, A.; Mironov, V. Phys. Status Solidi A 1994, 141,
471.
(40) Kumar, G. A.; Martinez, A.; Rosa, E. D. L. J. Lumin. 2002, 99,
141.
(41) Chen, B.; Dong, N.; Zhang, Q. J.; Yin, M.; Xu, J.; Liang, H.; Zhao,
H. J. Non-Cryst. Solids 2004, 341, 53.
(42) Jiang, H. D.; Wang, J. Y.; Zhang, H. J.; Hu, X. B.; Liu, H. J. Appl.
Phys. 2002, 92, 3647.
(43) (a) Speghini, A.; Peruffo, M.; Casarin, M.; Ajo`, D.; Bettinelli, M.
J. Alloys Compd. 2000, 300-301, 174. (b) Rolli, R.; Gatterer, K.; Wachtler,
M.; Bettinelli, M.; Speghini, A.; Ajo, D. Spectrochim. Acta A 2001, 57,
2009.
(44) Brown, D. C. In High-Peak-Power Nd:Glass Laser Systems;
Springer Series in Optical Science 25; Springer: Berlin, 1981.