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H. Wang et al. / Inorganic Chemistry Communications 14 (2011) 1183–1185
Fig. 1. The synthesis routine of the ligand HIDTFBD.
The europium(III) ternary complex was synthesized with a common
method analogoustoour earlierwork [11]asshown in Fig. 2 (yield 61%).
The EA data for Eu(IDTFBD)3phen (EuC51H39F9N8O6) were: found
(calculated)%: C, 51.76 (51.79); H, 3.351 (3.32); N, 9.482 (9.47).
To measure the lowest triplet state energy level of the ligand
HIDTFBD, gadolinium(III) binary complex Gd(IDTFBD)3·2H2O, was
also prepared in a similar method without phenanthroline (yield
61%). The EA data for Gd(IDTFBD)3·2H2O (GdC39H33F9N6O8) were:
found (calculated)%:C: 44.98 (44.96), H :3.16 (3.19), N:8.11 (8.07).
Compared to the free ligand HIDTFBD, a new and strong stretching
vibration peak near 1532 cm−1 in the complex reveals the presence of
the new C-C bond in the Eu(III) complex, which is the characteristic of
β-diketonate coordinated with rare earth ions. There were new weak
bonds in the complex near 490 cm−1 and 552 cm−1, which were
corresponding to the new bonds of Eu\N and Eu\O [12], respectively.
Thermogravimetric analysis (TG-DTG) showed that the decompo-
sition temperature of the complex Eu(IDTFBD)3phen is 323 °C, which
is high enough for the luminescence application since LEDs work
commonly under a temperature below 150 °C.
The UV–visible absorption spectra for the free ligands, EuCl3 and Eu
(IDTFBD)3phen in ethanol (1×10−5 mol L−1) are shown in Fig. 3. Since
the π-conjugated system in the complex molecule is expanded with
coordination of Eu3+ to IDTFBD− and phen, the absorption intensity of
the complex is remarkably enhanced and the absorption bands of the
complex appear in a wide range from 225 to 400 nm. Comparing the
absorption spectra of HIDTFBD, phen and Eu(IDTFBD)3phen, it is found
that the absorption band centering at 330 nm of the complex is mostly
attributed to the absorption of principal ligand IDTFBD− and the
absorption band of the secondary ligand phen is mainly located below
300 nm.
Fig. 3. The UV–visible absorption spectra of EuCl3, the ligands and the Eu(III)
complex in ethanol solution (1×10− 5 mol L− 1): (a) EuCl3, (b) phen, (c) HIDTFBD,
(d) Eu(IDTFBD)3phen.
absorbed energy by IDTFBD− ligand cannot be transferred to Gd3+ ion,
and phosphorescence of IDTFBD- appears when Gd(IDTFBD)3·2H2O is
excited by 430 nm light at 20 K. The lowest triplet state energy of the
ligand IDTFBD− T1(L), was determined by the shortest wavelength of the
phosphorescence peak of Gd(IDTFBD)3·2H2O to be E(T1)=18,416 cm−1
(543 nm), which is higher than the lowest excited state of Eu3+ 5D0
,
(17,267 cm−1) by 1149 cm−1. So the mechanism of the photolumines-
cence of the corresponding europium(III) complex was proposed as a
ligand-sensitized luminescence process (antenna effect) [13].
The fluorescence lifetime of Eu3+ in Eu(IDTFBD)3phen was
determined to be 357 μs by measuring the decay curve of 5D0→7F2
(610 nm) of theEu3+. Andthe curve wasfitted with a single exponential
function, which indicates that the Eu3+ ions in Eu(IDTFBD)3phen
molecules are located in the same parity sites. The luminescence
quantum yield for the Eu3+ complex was measured in solid state using
an integrating sphere based on the method described by Lin [14]. And
the luminescence quantum yield of the complex is φ=0.16, which is
good for a lanthanide organic complex. All the results indicate that the
complex is an efficient red phosphor under NUV excitation.
The photoluminescence excitation (PLE) and emission (PL) of the
Eu(III) complex powder are shown in Fig. 4, and the Eu(III) complex
exhibits high excitation intensity when monitored at 385 nm while
the excitation bands of the complex remains in a wider range due to
the formation of a big π-conjugated system in the complex molecule.
Exited by the NUV light, five characteristic Eu3+ luminescence peaks
appear at 578, 592, 610, 650 and 700 nm, which are due to 5D0 →7F0,
5D0 →7F1, 5D0 →7F2, 5D0 →7F3 and 5D0 →7F4 transitions, respectively.
The relative intensity of 5D0 →7F2 transition at 610 nm is the
strongest. Most importantly, the complex shows the highest excita-
tion intensity at around 370–395 nm, which is accurately matched
with the NUV-emitting from the InGaN chips.
Fig. 5 shows the emission spectra of the original LED without
phosphor (a) and the LED fabricated with the complex Eu(IDTFBD)3phen
and a 395 nm-emitting InGaN chip (b) under excitation of 20 mA
forward bias. The efficiency of the fabricated LED is 0.531 lm/W, much
higher than that of the original LED without phosphor (0.33 lm/W). The
CIE chromaticity coordinates of the LED are calculated as x=0.65 and
y=0.32, which are very close to the National Television Standard
Committee (NTSC) standard values for red (x=0.67 and y=0.33). A
photograph of the lighting red LED with Eu(IDTFBD)3phen is shown in
The coordination environment of Gd3+ ion in Gd(IDTFBD)3·2H2O is
similar to that of Eu3+ ion in Eu(IDTFBD)3·2H2O as the radius of Gd3+ ion
(94 pm) is close to that of Eu3+ ion (95 pm). The lowest excited state
energy level of Gd3+ ion, 6P7/2, is about 32,000 cm−1, much higher than
that of the lowest triplet energy level of the ligand IDTFBD− [T1(L)], so the
Fig. 2. The synthesis routine of the europium(III) complex Eu(IDTFBD)3phen.
Fig. 4. PLE (λem =610 nm) and PL (λex =385 nm) spectra of Eu(IDTFBD)3phen.
Wang, Huihui
