Luminescent properties of yttrium diphenylphosphinate activated by europium

Article abstract of DOI:10.1016/j.jallcom.2005.10.067

The synthesis and spectroscopic characterization of yttrium diphenylphosphinates doped with europium are reported. The purity of all samples was confirmed by carbon and hydrogen micro analysis, thermal analysis, IR vibrational spectroscopy, and X-ray diff

Full text of DOI:10.1016/j.jallcom.2005.10.067

Journal of Alloys and Compounds 418 (2006) 234–237
Luminescent properties of yttrium diphenylphosphinate
activated by europium
Cristina S. Francisco, Elizabeth B. Stucchi∗, Edson M. de Abreu
Instituto de Qu´ımica, UNESP, P.O. Box 355, 14800-900 Araraquara, SP, Brazil
Received 25 May 2005; received in revised form 25 August 2005; accepted 17 October 2005
Available online 19 January 2006
Abstract
The synthesis and spectroscopic characterization of yttrium diphenylphosphinates doped with europium are reported. The purity of all sam-
ples was confirmed by carbon and hydrogen micro analysis, thermal analysis, IR vibrational spectroscopy, and X-ray diffraction. Luminescence
spectra indicated the presence of two or more symmetry centers. The dynamic luminescence measurements suggested that one symmetry site
presented an inversion center, while the others had lower symmetry. The average quantum yield of Eu3+ emission in the yttrium matrices
was 60%.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Yttrium diphenylphosphinate; Luminescence spectroscopy; Europium; Quantum yield
1. Introduction
ble and kinetically inert complexes [4]. Additionally, it exhibits
a large absorption band in the UV region due to the aromaticity
of the phenyl groups [5].
In a previous work we have described the lumines-
cence properties of Eu(DPP)3 [6], Gd1−xEux(DPP)3 [7], and
La1−xEux(DPP)3 [8], with x varying from 0.50 to 0.99 (DPP, the
anion of the diphenylphosphinic acid). In the present paper, we
describe the synthesis, characterization and luminescent spec-
troscopic properties of the complexes Y1−xEux(DPP)3, with x
varying from 0 to 50% in molar concentration of Eu3+.
The search for efficient light-converting devices, based in
rare earth coordination compounds, has been a fascinating area
of interest in inorganic chemistry, due to their potential use as
luminescent materials [1]. In this area, the importance of the
lanthanoid ions luminescence is due to their unique long lifetime
and line-like emission bands, characteristic of the behavior of
their 4f states in the presence of a chemical environment [2].
In lanthanoid ion complexes with encapsulating ligands, an
intense luminescence of the ion may, in principle, be obtained
by the “antenna effect”, which is defined as a light conversion
process via an absorption-energy transfer-emission sequence
involving distinct absorbing (ligand, light collector) and emit-
ting (metal ion) components. In such a process, the quantities
that contribute to the luminescence intensity are: (i) the intensity
of the ligand absorption, (ii) the efficiency of the ligand-to-metal
energy transfer, and (iii) the efficiency of the metal luminescence
[3]. An interesting ligand in this respect is diphenylphosphinic
acid: it reacts promptly with the chlorides of the lanthanoids,
resulting in insoluble, non-hygroscopic, thermodynamically sta-
2. Methodology
2.1. The preparation of yttrium and europium chlorides and
yttrium diphenylphosphinates doped with europium
Eu2O3, Y2O3 (Aldrich, 99.99%) and diphenylphosphinic acid (Aldrich,
99%) were used. EuCl3 and YCl3 were prepared by dissolving the respective
oxides in 1.0 mol L−1 hydrochloric acid. The pH was then adjusted to 3–4 with
water, and the water was systematically replaced by ethanol through successive
evaporations. The yttrium diphenylphosphinates doped with europium were pre-
pared at 40 ◦C through the mixture of the appropriate amounts of 0.1 mol L−1
solutions of EuCl3 and YCl3 with ethanol solutions of diphenylphosphinic acid
in a metal:ligand molar ratio of 1:4. The complexes were washed with ethanol
and dried in an Abderhalden apparatus at 78 ◦C.
∗
Consistentanalyticalvaluesataround56%C, 4.18%Hindicatedtherequired
metal to ligand ratio of 1:3 in the products.
Corresponding author. Tel.: +55 16 3301 6635; fax: +55 16 3322 7932.
E-mail address: berwerth@iq.unesp.br (E.B. Stucchi).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.10.067

C.S. Francisco et al. / Journal of Alloys and Compounds 418 (2006) 234–237
235
Table 1
X-ray data for Y0.90Eu0.10(DPP)3
˚
˚
˚
˚
d (A)
I/I0
d (A)
I/I0
d (A)
I/I0
d (A)
I/I0
12.01
6.93
5.08
100.0
5.02
7.30
4.50
4.28
4.17
15.77
14.65
10.01
3.88
3.48
3.42
8.15
6.96
5.19
3.11
2.84
1.99
6.00
5.80
5.15
Fig. 1. TG and DTA curves for Y0.90Eu0.10(DPP)3.
2.2. Measurements
Carbon and hydrogen contents were determined using a CE Instruments
EA 1110 elemental analyzer. X-ray powder diffraction patterns were obtained
using a Siemens D5000 diffractometer with Cu K␣ radiation. Differential ther-
mal analysis and thermogravimetric curves were obtained in a TA Instruments
SDT2960 thermoanalyser. The 4000–400 cm−1 IR spectrum was recorded using
KBr pellets on an FT-IR Perkin Elmer-2000 spectrophotometer. For the excita-
tion and emission spectra the samples were excited using a 450 W xenon lamp,
at 298 K. The appropriate wavelengths were selected. The luminescence spec-
tra, kinetic measurements and diffuse reflectance curves were recorded on a
Spectrofluorometer Fluorolog Spex 212L and a Spex 1934 Phosphorimeter.
The emission quantum yield q for the Y1−xEux(DPP)3 compounds were
obtained following the procedure described in Ref. [9]. The values obtained are
accurate to within 10% [10]. The standard phosphors used was similar to YOX
U719 Philips (Y2O3:3%Eu3+, x = 610 nm and q = 99%).
Fig. 2. (a) Excitation and (b) emission spectra for Y0.90Eu0.10(DPP)3 obtained
at room temperature.
the P(O)OH group, namely those between 3650 and 3100, 2900
and 1900 cm−1 (νO–H) and around 1600 cm−1 (δO–H) were sup-
pressed in the spectra of the products, an additional the νPO shift
from 1184 and 1130 to 1148 and 1056 cm−1, respectively.
The X-ray diffraction patterns (Table 1) indicate that all the
new compounds are isomorphs and similar to the lanthanum and
gadolinium series [6,8], which were shown to adopt the unitary
cell parameters of the triclinic crystalline system.
3. Results and discussions
The infrared spectra of the powders were unambiguous
to show the coordination between the metal cations and the
anion of the diphenylphosphinic acid; all the absorption bands
attributed to the several vibrational modes of the O–H bond in
The TG and DTA curves (Fig. 1) indicate de quite unusual
absence of water in the metals coordination sites, in agreement
Table 2
Lifetime for yttrium diphenylphosphinates doped with different europium concentration
Eu (mol%)
Lifetime (ms)
λexc = 273 nm
λem = 592 nm
λexc = 392 nm
λexc = 465 nm
λem = 592 nm
λem = 611 nm
λem = 592 nm
λem = 611 nm
λem = 611 nm
1
5
10
20
50
7.38
4.83
6.70
6.46
5.71
6.45/4.96
5.42
5.42
5.56
7.55
6.33
5.57
5.14
5.12
4.75
6.72/4.56
4.90/1.61
4.30
4.33
4.34
6.55
5.67
4.26
4.82
6.12/2.71
4.90/2.15
4.08
4.10
4.12
5.22/4.60

236
C.S. Francisco et al. / Journal of Alloys and Compounds 418 (2006) 234–237
Table 3
with the IR spectral analysis; these observations can be directly
related to the kinetic inertness of the new compounds. The TG
data are also unusual, in which they show that the new com-
pounds are thermostable up to about 500 ◦C.
Quantum yield values for yttrium diphenylphosphinates doped with different
europium concentration
Eu (mol%)
Quantum yield
The excitation and emission spectra for the Y0.90Eu0.10
(DPP)3 are very similar for all samples and are shown in Fig. 2.
The broad and symmetric band at 273 nm is caused by the
absorption of the phenyl rings of the ligands, and dominates the
1
5
10
20
59.14
58.10
60.33
59.19
spectra. The bands at 392 and 465 nm are attributed to the Eu3+
7
5
7
5
4f6 intra shell F0 → L6 and F0 → D2 transitions, respec-
tively. Since these absorption peaks are very weak as compared
to the intensity of the band at 273 nm, it is suggested that the
ligand excitation is the preferential path for luminescence sen-
sitization in these compounds. The emission spectra observed
resulted from the relaxation of the first 5D0 excited state of Eu3+
to the first five levels of 7Fj (j = 0–4) ground state.
For the same concentrations of Eu3+ ion, the relative inten-
5
7
7
sities D0 → F1/5D0 → F2 increase with different excitation
wavelengths. This behavior indicates the contribution of two or
more Eu3+ symmetry sites and that the no center symmetric ones
are favored when the samples are excited in the 392 and 465 nm
bands. The time resolved spectra (Fig. 3) clearly evidences such
5
7
an observation, since the D0 → F2 transition becomes more
intense when the excitation is performed directly in the Eu+3
absorption bands.
The luminescence lifetimes were calculated based on the
decay curves and are listed in Table 2. These values are rela-
tively high for lanthanoid complexes, and suggest that the bonds
between oxygen and europium are intrinsically ionic. The range
of about 3 ms in the lifetime values for the series of new com-
pounds may also be interpreted as the contribution of the energy
transfer processes between the different symmetry Eu+3 sites
in the complexes. However, the average quantum yield of Eu3+
emission in the yttrium matrices is 60% (Table 3). This value is
relatively high for lanthanoid complexes [1,11,12] and no con-
centration quenching was observed. This data, together with the
lifetime values observed, suggest that the activators are evenly
distributed throughout the host matrix, in a somewhat clear evi-
dence of an overall polymeric structure for the new materials.
4. Conclusions
The study of Y1−xEux(DPP)3 by various techniques suggest
that these compounds adopt polymeric structures, composed by
symmetry site mixtures, which renders unusual characteristics
for lanthanoid complexes, such as high thermal stability, kinetic
inertness towards water ligand exchange, high lifetime values
and reasonable quantum yields. These properties are expected
for materials with potential applications in molecular light con-
version devices.
Acknowledgements
The authors acknowledge CAPES, FUNDUNESP and
FAPESP (Brazilian agencies) for financial support. They are
Fig. 3. Time resolved spectra for Y0.90Eu0.10(DPP)3 obtained at room temper-
ature.

C.S. Francisco et al. / Journal of Alloys and Compounds 418 (2006) 234–237
237
grateful to Dr. Sidney J.L. Ribeiro (UNESP, Brazil) for help with
the measurements of quantum yield and useful discussions, and
to Dr. Stanlei I. Klein (UNESP, Brazil) for the revision of the
manuscript.
[4] P.O. Dustan, G. Vicentini, An. Acad. Bras. Cienc. 47 (1975) 97–100.
[5] D.J. Fife, K.W. Morse, W.M. Moore, J. Photochem. 24 (1984) 249–263.
[6] E.B. Stucchi, S.L. Scarpari, M.A.C. Dos Santos, S.R.A. Leite, J. Alloys
Compd. 275–277 (1998) 89–92.
[7] S.L. Scarpari, E.B. Stucchi, J. Alloys Compd. 323 (2001) 740–
742.
[8] E.M. Abreu, E.B. Stucchi, S.L. Scarpari, Proceedings of Reunia˜o Anual
da Sociedade Brasileira de Qu´ımica, vol. 25, 2002, p. QI-137.
[9] F.R.G. e Silva, J.F.S. Menezes, G.B. Rocha, S. Alves, H.F. Brito, R.L.
Longo, O.L. Malta, J. Alloys Compd. 303–304 (2000) 364–370.
[10] A. Bril, A.W. De Jager-Veenis, J. Eletrochem. Soc. 123 (1976) 396–398.
[11] C.A. Kodaira, H.F. Brito, O.L. Malta, O.A. Serra, J. Lumin. 101 (1–2)
(2003) 11–21.
References
[1] M.E. Mesquita, F.R.G. Silva, R.Q. Albuquerque, R.O. Freire, E.C.
Conceic¸a˜o, J.E.C. Silva, N.B.C. Ju´nior, G.F. De Sa´, J. Alloys Compd.
366 (2004) 124–131.
[2] M.E. Mesquita, G.F. De Sa´, M.A.B. Lopes, O.L. Malta, J. Chem. Res.
(S) 2 (1996) 120–121.
[12] A.M. Klonkowski, S. Lis, M. Pietraszkiewicz, Z. Hnatejeko, K.
Czarnobaj, M. Elbanowski, Chem. Mater. 15 (2003) 656–663.
[3] N.S. Sabbatini, M. Guardigli, M.J. Lehn, Coord. Chem. Rev. 123 (1–2)
(1993) 201–228.