Synthesis and photophysical properties of a highly luminescent EuIII-containing hybrid thin film

Article abstract of DOI:10.1016/j.poly.2016.07.034

A luminescent thin film, Eu@glass, has been prepared on the surface of glass substrates from a silylated diamidopyridyl ligand L and the complex [Eu(dbm)₃(H₂O)₂] (Hdbm?=?dibenzoylmethane) via a sol–gel method. The Eu@glass exhibits intense red photoluminescence under the irradiation of near UV light with a quantum yield of 26%. Compared to the compound [Eu(dbm)₃(H₂O)₂], the photoluminescence intensity of Eu@glass is dramatically enhanced, and the emission lifetime of Eu^III(0.517?ms) is more than an order of magnitude longer.

Full text of DOI:10.1016/j.poly.2016.07.034

Polyhedron 118 (2016) 25–29
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and photophysical properties of a highly luminescent
III
Eu -containing hybrid thin film
⇑
Xue Liu, Elisabeth Bouwman
Leiden Institute of Chemistry, Gorlaeus Laboratories Leiden University, P.O. Box 9502, 2300 RA Leiden, The, Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
A luminescent thin film, Eu@glass, has been prepared on the surface of glass substrates from a silylated
Received 2 May 2016
Accepted 25 July 2016
Available online 30 July 2016
diamidopyridyl ligand L and the complex [Eu(dbm)
method. The Eu@glass exhibits intense red photoluminescence under the irradiation of near UV light with
a quantum yield of 26%. Compared to the compound [Eu(dbm) (H O) ], the photoluminescence intensity
3 2 2
(H O) ] (Hdbm = dibenzoylmethane) via a sol–gel
3
2
2
III
of Eu@glass is dramatically enhanced, and the emission lifetime of Eu (0.517 ms) is more than an order
of magnitude longer.
Keywords:
Europium
Luminescence
Film
Ó 2016 Elsevier Ltd. All rights reserved.
Sol–gel
Hybrid material
1
. Introduction
In this paper, we report the synthesis of the new silylated diami-
III
dopyridyl ligand
L (Scheme 1) and the corresponding Eu
The photoluminescent properties of lanthanoid compounds
organic-inorganic silicate hybrid film. The thin film on the surface
of glass has been obtained via a sol–gel process.
have drawn extensive attention due to their attractive features,
such as characteristic sharp-line emissions, long emission lifetimes
III
and high quantum yields [1–4]. These features make Ln -based
2
. Experimental
materials suitable for use in a wide range of applications, such as
sensing [5–11], imaging [12,13], and phosphors in lighting
2.1. Materials
[
14–18]. Due to the nature of the 4f–4f transition, the direct excita-
III
tion of Ln is rather inefficient. In lanthanoid complexes, the photon
All chemicals and solvents were purchased from commercial
energy can be absorbed efficiently by its surrounding organic ligands
sources and used without further purification. The compound
Eu(dbm) (H O) ] (Hdbm = dibenzoylmethane) was synthesized
III
upon which energy is transferred to the Ln emitting center, a
[
3
2
2
phenomenon that is known as the ‘‘antenna effect” [19,20].
following a literature procedure [37]. IR spectra were recorded
on a Perkin Elmer UATR Two FT-IR spectrometer set to a resolution
The rather poor mechanical properties of lanthanoid complexes
limit their technological applications [21,22]. One of the solutions
is to introduce the lanthanoid complex into a polymer or silica-
based matrix, which can be used to fabricate luminescent thin
films [23–31]. Transparent luminescent thin films containing
lanthanoid complexes have been demonstrated to be useful for
application in agriculture and horticulture [32,33], lighting [34],
Si-based solar cells [35] and as luminescent solar concentrators
ꢀ1
of 4 cm . The solid-state excitation spectra were recorded using a
Shimadzu RF-5301PC spectrofluorophotometer. The solid-state
emission spectra were recorded with an irradiation-calibrated
CCD sensor (Avantes AvaSpec-2048UA). Solid-state absorption
spectra were recorded with the Avantes absorbance setup, using
the Avantes AvaSpec-2048UA CCD spectrometer as detector, and
the AvaLight-DH-S Deuterium-Halogen light source. The fluores-
cence lifetime was measured using a Hamamatsu R928P photo-
multiplier connected to a Tektronix DPO4054 digital scope, a Carl
Zeiss M20 grating monochromator was used to select the emission
wavelength. A Labview program was used to collect and to average
the data. Excitation was done with an Ekspla NTB342B Nd:YAG
laser equipped with a OPO and SHG to generate 5 ns pulses at a
10 Hz rate. The photoluminescence quantum yield was determined
using the absolute method [38]. An integrating sphere (Avantes
(
LSCs) [21,36].
The purpose of the research reported in this paper was to
develop a new ligand that is able to bind europium and create a
thin layer on glass surfaces. Such material potentially can been
applied as luminescent solar concentrator or in Si-based solar cells.
⇑
Corresponding author.
E-mail address: bouwman@chem.leidenuniv.nl (E. Bouwman).
http://dx.doi.org/10.1016/j.poly.2016.07.034
277-5387/Ó 2016 Elsevier Ltd. All rights reserved.
0

2
6
X. Liu, E. Bouwman / Polyhedron 118 (2016) 25–29
Scheme 1. Synthesis route of the ligand L.
AvaSphere 30REFL) was connected to an irradiance-calibrated CCD
spectrometer (Avantes AvaSpec-2048UA). A 1000 W Xenon lamp
1003 (w), 953 (m), 847 (w), 775 (m), 748 (m), 681 (m), 646 (m),
ꢀ1
479 (w) cm
.
(
LOT) and a Spex monochromator were used as the excitation
source.
2.2.4. Preparation of luminescent hybrid material SiAEu
The ligand (6.7 mol, 5.0 mg) and [Eu(dbm)
(3.3 mol, 2.8 mg) were dissolved in 5 ml of a mixture of EtOH/
O = 9.5:0.5, and stirred at room temperature for 3 days. The
L
l
3 2 2
(H O) ]
2
2
.2. Ligand synthesis
l
H
2
.2.1. Dimethyl pyridine-2,6-dicarboxylate (1)
white powder precipitate was collected by filtration, washed with
Thionyl chloride (26.80 ml, 372 mmol) was added dropwise to
acetone, and dried at 50 °C.
methanol (125 ml) at 0 °C, then solid 2,6-pyridinedicarboxylic acid
10.00 g, 60 mmol) was added to this solution. The reaction mix-
(
2.2.5. Preparation of luminescent silica film (Eu@glass)
Glass substrates (CorningÒ cover glass, 18 ꢁ 18 mm) were
cleaned with acetone in an ultrasonic bath for 5 min, then dried
in the oven. The substrates were immersed in a mixture of hydro-
ture was stirred at room temperature for 18 h, and then refluxed
for 2 h. After evaporation of the solvent, the residue was dissolved
in diethyl ether (150 ml) and washed with water (3 ꢁ 30 ml). The
organic layer was dried with anhydrous MgSO
4
and the solvent
gen peroxide and sulfuric acid, and then stored in distilled H
[Eu(dbm) (H O) ] (3.3 mol, 2.8 mg) was dissolved in a solution
of ligand L (6.7 mol, 5.0 mg) in 5 ml of a mixture of EtOH/
O = 9.5:0.5, and the reaction mixture was stirred at room tem-
2
O.
was evaporated in vacuo. The crude product was used in the next
3
2
2
l
1
step reaction without further purification. Yield: 11.01 g, 94%.
NMR (300 MHz, CDCl ): d = 8.33 (d, J = 7.8 Hz, 2H, Ph), 8.05 (t,
J = 7.8 Hz, 1H, Ph), 4.04 (s, 6H, CH ):
) ppm. 13C NMR (75 MHz, CDCl
H
l
H
2
3
perature for 30 min. A transparent thin film was prepared by
spin-coating of two drops of this solution on the surface of glass
substrates at spin rate of 3000 rpm. A non-transparent film was
made by dropping the solution onto a glass substrate, which was
then dried in air.
3
3
d = 165.0, 148.2, 138.4, 128.0, 53.2 ppm.
0
2
.2.2. N,N -bis(2-aminoethyl)-2,6-pyridinedicarboxylic diamide (2)
Intermediate 2 was synthesized following a literature proce-
dure [39]. 1,2-Diaminoethane (8.95 g, 149 mmol) was added to a
solution of 1 (4.00 g, 20.4 mmol) in 200 ml methanol, and the mix-
ture was stirred at room temperature for 12 h. After the reaction,
the formed precipitate (oligomeric by-products) was removed by
filtration and the filtrate was evaporated in vacuo. The residue
was dissolved in 30 ml butanol and evaporated to dryness to fur-
ther remove 1,2-diaminoethane. A yellowish solid was obtained,
3. Results and discussion
3.1. Synthesis and characterization
The ligand L was synthesized following the procedure in
Scheme 1 in an overall yield of 23%. The ligand was mixed into
an ethanol-water solution containing the compound [Eu(dbm)3
(H O) ], yielding a transparent solution that was either spin-coated
which was used in the next step without further purification. Yield:
1
4
3
.84 g, 95%. H NMR (300 MHz, MeOD): d = 8.31–8.14 (m, 3H, Ph),
2
2
1
3
.55 (t, J = 6.3 Hz, 4H, CH
2 2
), 2.93 (t, J = 6.3 Hz, 4H, CH ) ppm.
C
or drop-casted onto a thoroughly cleaned and pre-treated glass
plate. Drop-casting resulted in a non-transparent film, whereas
spin-coating led to a clear and transparent film. In the description
below the resulting films are indicated as Eu@glass.
NMR (75 MHz, MeOD): d = 164.9, 148.8, 139.1, 124.4, 41.8,
4
0.8 ppm.
2.2.3. Ligand L
The FTIR spectra of the compound [Eu(dbm)
3 2
(H O)
2
], the ligand
To a solution of 2 (2.56 g, 10.2 mmol) in 200 ml toluene was
L and the powder SiAEu are shown in Fig. 1. The broad peak at
ꢀ
1
added 3-triethoxysilanylpropyl isocyanate (5.54 g, 22.4 mmol),
the mixture was refluxed for 24 h, after which the solvent was
removed and the oil was kept at ꢀ20 °C. The resulting white pre-
cipitate was collected by filtration, washed with diethyl ether
3351 cm
in the FTIR spectrum of [Eu(dbm)
3
(H O)
2 2
] can be
assigned to the presence of the two water molecules (trace a,
ꢀ1
Fig. 1), whereas the peaks at 1595 and 1454 cm are assigned to
the stretching vibration of the carbonyl groups of the dbm ligand
and dried in vacuo. Yield: 2.01 g, 26%. 1H NMR (300 MHz, CDCl
[40,41]. The absorbances in the range of 750–680 cm
ꢀ1
are
3
,
Fig. S1): d = 8.28 (d, J = 7.8 Hz, 2H, Ph), 8.00 (t, J = 7.5 Hz, 1H, Ph),
assigned to the CAH out-of-plane wagging of the phenyl rings in
the dbm ligand [25,42]. In the FTIR spectrum of the ligand L, the
3
3
.84 (q, J = 7.0 Hz, 12H, OCH
.49 (m, 4H, CH ), 3.16 (q, J = 6.7 Hz, 4H, CH
), 1.20 (t, J = 7.8 Hz, 18H, CH ), 0.61 (t, J = 8.1 Hz, 4H, CH
, Fig. S2): d = 164.4, 160.0, 148.6,
38.9, 124.2, 58.5, 43.1, 41.7, 39.8, 23.6, 18.4, 7.6 ppm. Selected
IR data (v): 3284 (m), 2968 (m), 2929 (m), 2886 (m), 1664 (m),
2
Me), 3.69–6.60 (m, 4H, CH
2
), 3.60–
ꢀ1
ꢀ1
2
2
), 1.69–1.60 (m, 4H,
peaks at 1637 cm
(C@O stretching vibration) and 1547 cm
CH
ppm. C NMR (75 MHz, CDCl
1
2
3
2
)
(NAH bending vibration) are assigned to the amide groups (trace
1
3
ꢀ1
3
b, Fig. 1) [30]. The peaks at 1074 and 479 cm belong to the
stretching and bending vibration of the SiAO groups, respectively
ꢀ1
[43]. The broad peak at 3284 cm can be assigned to the stretch-
ing vibration of the amide NAH. In addition to the NMR spectra
this IR spectrum supports that the ligand L was synthesized
1
1
637 (m), 1547 (s), 1497 (m), 1446 (m), 1389 (w), 1359 (w),
291 (m), 1268 (m), 1249 (m), 1167 (m), 1100 (s), 1074 (vs),

X. Liu, E. Bouwman / Polyhedron 118 (2016) 25–29
27
successfully. In the FTIR spectrum of SiAEu, a broad band centered
ꢀ1
at 1039 cm (SiAOASi asymmetric stretching vibration) indicates
the successful formation of the SiAOASi framework (trace c, Fig. 1)
[
1
22,23,44]. Furthermore, the two strong absorptions at 1661 and
535 cm assigned to the amide groups are slightly shifted com-
ꢀ1
pared to the spectrum of the ligand L, which might be ascribed to
III
the coordination of ligand L to Eu via the pyridine nitrogen and
the amide carbonyl oxygens [45].
3 2 2
The solid-state absorption spectra of [Eu(dbm) (H O) ], SiAEu
and ligand L are shown in Fig. 2. Only a narrow absorption peak
with a maximum at 275 nm in is present in the absorption spec-
trum of ligand L. Compared to the broad absorption peak in the
spectrum of [Eu(dbm) (H O) ], the spectrum of SiAEu is narrower
3 2 2
in the blue region. Furthermore, the hybrid material SiAEu does
not show absorption at wavelengths higher than 500 nm, which
III
means that any luminescent emission from the Eu center cannot
be reabsorbed by SiAEu; the negative peaks in the SiAEu absorp-
III
tion spectrum are due to emission of the Eu center.
3 2 2
Fig. 1. FTIR spectra of (a) [Eu(dbm) (H O) ] (b) ligand L and (c) SiAEu.
Fig. 2. Solid state absorption spectra of [Eu(dbm)
3
(H
2
O)
2
], SiAEu and ligand L.
Fig. 4. Excitation (left) and emission (right) spectra of Eu@glass.
Fig. 3. Pictures of [Eu(dbm)
b and e); Eu@glass on glass substrate obtained by spin coating (c and f). (a, b and c) ambient light; d, e and f: 366 nm UV light. In (f), the red emission is concentrated to the
border of glass due to total internal reflection [51]. (Colour online.)
3 2 2
(H O) ] (yellow solid in vial) and the hybrid gel (transparent liquid in vial; a and d); Eu@glass on a glass substrate obtained by drop-casting
(

2
8
X. Liu, E. Bouwman / Polyhedron 118 (2016) 25–29
3 2 2
Fig. 5. The decay curves of (a) [Eu(dbm) (H O) ]; (b) Eu@glass monitored at 615 nm (kex = 355 nm).
3.2. Luminescent properties
3 2 2
[Eu(dbm) (H O) ]. The film exhibits bright red luminescence under
the excitation of near UV light. The considerable enhanced emis-
sion intensity and longer lifetime of the Eu@glass film confirm
the coordination of the ligand L to the Eu ion, as it indicates the
Under the irradiation of a high-pressure Hg lamp (366 nm),
Eu(dbm) (H O) ] shows very weak red emission (Fig. 3a and d);
III
[
3
2
2
the weak emission is ascribed to quenching of the high-energy
state through coupling with the OAH oscillators of the coordinated
water molecules [46–50]. In contrast, the drop-casted Eu@glass
exhibits an intense red-color emission (Fig. 3e). The transparent
film Eu@glass prepared by spin-coating only exhibits red-color
emission at the borders of the glass plate due to total internal
reflection [51] (Fig. 3f).
reduction of the quenching effect by coordinated water molecules.
Acknowledgements
X. Liu gratefully acknowledges a grant from the Chinese Schol-
arship Council (no. 201206250014). We are grateful to dr. Hong
Zhang and Mr. Michiel Hilbers from the University of Amsterdam
for the use of their facilities and assistance in the lifetime
measurements.
The excitation and emission spectra of the film Eu@glass have
been recorded (Fig. 4). Upon excitation with 385 nm UV light the
emission spectrum of Eu@glass shows the five emission peaks that
III
are characteristic for the Eu ion at 578, 590, 615, 652 and 699 nm,
5
7
arising from the D
0
? F
J
(J = 0–4) transitions. No phosphorescence
Appendix A. Supplementary data
emission from the ligand is observed, indicating an efficient
energy-transfer process from the excited state of the ligand to
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2016.07.034.
III
5
7
0 1
the Eu ion. The emission peak at 590 nm ( D ? F ) is a magnetic
dipole (MD) transition and its intensity is insensitive to the coordi-
5
7
0 2
nation environment. However, the D ? F transition at 615 nm is
References
a forced electric dipole (ED) transition and its intensity is sensitive
III
to the Eu surroundings [52]. The emission spectrum is dominated
[1] Z.S. Dou, J.C. Yu, Y.J. Cui, Y. Yang, Z.Y. Wang, D. Yang, G.D. Qian, J. Am. Chem.
Soc. 136 (2014) 5527.
[2] P.A. Tanner, Chem. Soc. Rev. 42 (2013) 5090.
5
7
by the D
the D
0
? F
2
transition at 615 nm and the emission intensity of
5
7
0
? F
1
transition is rather weak, indicating lack of an inver-
[
3] D. Parker, Chem. Soc. Rev. 33 (2004) 156.
III
3 2 2
sion center at the Eu site [53]. Compared to [Eu(dbm) (H O) ],
[4] S.V. Eliseeva, J.C.G. Bunzli, Chem. Soc. Rev. 39 (2010) 189.
[
5] X. Liu, S. Akerboom, M. de Jong, I. Mutikainen, S. Tanase, A. Meijerink, E.
Bouwman, Inorg. Chem. 54 (2015) 11323.
the significant luminescence enhancement of Eu@glass gives a
III
strong indication that the ligand L is coordinated to the Eu emit-
[
6] J.M. Zhou, W. Shi, N. Xu, P. Cheng, Inorg. Chem. 52 (2013) 8082.
ting center, having replaced the water molecules. The emission
quantum yield of the Eu@glass has been measured using the abso-
lute method and was calculated to be 26% [38]. The emission of [Eu
[7] J. Zhou, H. Li, H. Zhang, H. Li, W. Shi, P. Cheng, Adv. Mater. 27 (2015) 7072.
[8] H.G. Li, R.F. Lan, C.F. Chan, L.J. Jiang, L.X. Dai, D.W.J. Kwong, M.H.W. Lam, K.L.
Wong, Chem. Commun. 51 (2015) 14022.
[
9] Z.H. Liang, T.H. Tsoi, C.F. Chan, L.X. Dai, Y.D. Wu, G.Y. Du, L.Z. Zhu, C.S. Lee, W.T.
Wong, G.L. Law, K.L. Wong, Chem. Sci. 7 (2016) 2151.
(
3 2 2
dbm) (H O) ] is too weak for quantum yield determination in our
setup, but has been reported to be 1% [49].
[10] X. Liu, W.T. Fu, E. Bouwman, Chem. Commun. 52 (2016) 6926.
[11] X. Liu, M.A. Siegler, E. Bouwman, Eur. J. Inorg. Chem. 2016 (2016) 2984.
5
The D
the compound [Eu(dbm)
curves display mono-exponential behavior. The emission lifetime
0
decay curves monitored at 615 nm for the Eu@glass and
[
[
12] M.C. Heffern, L.M. Matosziuk, T.J. Meade, Chem. Rev. 114 (2013) 4496.
13] J.C.G. Bünzli, Chem. Rev. 110 (2010) 2729.
3
(H O) ] are shown in Fig. 5. Both decay
2
2
[14] Y. Lu, B. Yan, Chem. Commun. 50 (2014) 15443.
[15] D. Ma, X. Li, R. Huo, J. Mater. Chem. C 2 (2014) 9073.
III
of the Eu ion in [Eu(dbm)
3
(H
2 2
O) ] is 0.048 ms, whereas the life-
[
[
16] A.R. Ramya, S. Varughese, M.L.P. Reddy, Dalton Trans. 43 (2014) 10940.
17] X.Y. Xu, B. Yan, Dalton Trans. 44 (2015) 1178.
III
time of the Eu emission in Eu@glass is 0.517 ms. The shorter
emission lifetime of the Eu ion in [Eu(dbm)
III
(H
3 2
O)
2
] is due to
[18] X. Liu, S. Akerboom, S.H.C. Askes, I. Mutikainen, E. Bouwman, Inorg. Chem.
Commun. 61 (2015) 60.
the quenching of the emission by the coordinated water molecules.
The dramatically longer lifetime of emission in the Eu@glass fur-
ther demonstrates that the ligand L is coordinated to the Eu ion.
[
[
19] E.G. Moore, A.P. Samuel, K.N. Raymond, Acc. Chem. Res. 42 (2009) 542.
20] Y.W. Yip, H.L. Wen, W.T. Wong, P.A. Tanner, K.L. Wong, Inorg. Chem. 51 (2012)
7013.
III
[
21] V.T. Freitas, L.S. Fu, A.M. Cojocariu, X. Cattoën, J.R. Bartlett, R. Le Parc, J.L.
Bantignies, M.W.C. Man, P.S. André, R.A.S. Ferreira, L.D. Carlos, A.C.S. Appl,
Mater. Interfaces 7 (2015) 8770.
4
. Conclusion
[
22] A.C. Franville, D. Zambon, R. Mahiou, S. Chou, Y. Troin, J.C. Cousseins, J. Alloys
Compd. 275–277 (1998) 831.
The luminescent thin film, Eu@glass, has been prepared on a
glass surface via a sol–gel method using a silylated ligand L and
[
23] X.M. Guo, J.L. Canet, D. Boyer, A. Gautier, R. Mahiou, J. Mater. Chem. 22 (2012)
6117.

X. Liu, E. Bouwman / Polyhedron 118 (2016) 25–29
29
[
[
24] B. Lebeau, J. Maquet, C. Sanchez, F. Beaume, F. Laupretre, J. Mater. Chem. 7
1997) 989.
25] G. Dovbeshko, O. Fesenko, R. Fedorovich, T. Gavrilko, A. Marchenko, G.
Puchkovska, L. Viduta, A. Naumovets, D. Chubich, A. Vitukhnovskii, D. Fichou, J.
Mol. Struct. 792–793 (2006) 115.
26] S. Kumar, M.S. Hundal, N. Kaur, R. Singh, H. Singh, G.H.N. Sood, M.M. Ripoll, J.S.
Aparicio, J. Org. Chem. 61 (1996) 7819.
27] C.D. Ki, C. Oh, S.G. Oh, J.Y. Chang, J. Am. Chem. Soc. 124 (2002) 14838.
28] M. Martínez-Calvo, O. Kotova, M.E. Möbius, A.P. Bell, T. McCabe, J.J. Boland, T.
Gunnlaugsson, J. Am. Chem. Soc. 5 (2015) 1983.
29] P. Hesemann, J.J.E. Moreau, Tetrahedron Asymmetry 11 (2000) 2183.
30] A. Aydogan, A. Akar, Tetrahedron Lett. 52 (2011) 2790.
31] M. Bredol, M. Schem, Opt. Mater. 27 (2004) 521.
32] J. Graffion, X. Cattoën, M.W.C. Man, V.R. Fernandes, P.S. André, R.A.S. Ferreira, L.
D. Carlos, Chem. Mater. 23 (2011) 4773.
[39] L.H. Cai, P.Z. Hu, X.L. Du, L.X. Zhang, Y. Liu, Indian J. Chem. B 46 (2007) 523.
[40] Q.G. Meng, P. Boutinaud, A.C. Franville, H.J. Zhang, R. Mahiou, Microporous
Mesoporous Mater. 65 (2003) 127.
[41] Z.Q. Bian, K.Z. Wang, L.P. Jin, Polyhedron 21 (2002) 313.
[42] E. Moretti, A. Talon, L. Storaro, A. Le Donne, S. Binetti, A. Benedetti, S. Polizzi, J.
Lumin. 146 (2014) 178.
[43] H.R. Li, J. Lin, H.J. Zhang, H.C. Li, L.S. Fu, Q.G. Meng, Chem. Commun. (2001)
1212.
[44] C. Malba, U.P. Sudhakaran, S. Borsacchi, M. Geppi, F. Enrichi, M.M. Natile, L.
Armelao, T. Finotto, R. Marin, P. Riello, A. Benedetti, Dalton Trans. 43 (2014)
16183.
[45] X.H. Peng, Y.J. Wang, X.L. Tang, W.S. Liu, Dyes Pigm. 91 (2011) 26.
[46] G. Blasse, N. Sabbatini, Mater. Chem. Phys. 16 (1987) 237.
[47] M.T. Berry, P.S. May, H. Xu, J. Phys. Chem. 100 (1996) 9216.
[48] S. Petoud, J.C.G. Bünzli, T. Glanzman, C. Piguet, Q. Xiang, R.P. Thummel, J.
Lumin. 82 (1999) 69.
[49] E. Niyama, H.F. Brito, M. Cremona, E.E.S. Teotonio, R. Reyes, G.E.S. Brito, M.C.F.
C. Felinto, Spectrochim. Acta, Part A 61 (2005) 2643.
[50] A.F. Kirby, F.S. Richardson, J. Phys. Chem. 87 (1983) 2544.
[51] S. Mirershadi, S. Ahmadi-Kandjani, Dyes Pigm. 120 (2015) 15.
[52] F.S. Richardson, Chem. Rev. 82 (1982) 541.
(
[
[
[
[
[
[
[
[
[
[
33] K. Binnemans, Chem. Rev. 109 (2009) 4283.
34] S.Y. Kwak, S.C. Yang, N.R. Kim, J.H. Kim, B.S. Bae, Adv. Mater. 23 (2011) 5767.
35] L.D. Carlos, R.A.S. Ferreira, V. de Zea Bermudez, B. Julian-Lopez, P. Escribano,
Chem. Soc. Rev. 40 (2011) 536.
[
36] O.M. ten Kate, K.W. Krämer, E. van der Kolk, Sol. Energy Mater. Sol. Cells 140
(
2015) 115.
[
[
37] R.G. Charles, A. Perrotto, J. Inorg. Nucl. Chem. 26 (1964) 373.
38] J.C.D. Mello, H.F. Wittmann, R. Friend, Adv. Mater. 9 (1997) 230.
[53] S. Akerboom, M.S. Meijer, M.A. Siegler, W.T. Fu, E. Bouwman, J. Lumin. 145
(2014) 278.