Resonance light scattering properties of Eu3+ in gold colloid

Article abstract of DOI:10.1016/j.saa.2004.11.018

Gold colloidal containing rare-earth ions Eu³⁺ were prepared at room temperature. Fluorescence spectra and resonance light scattering (RLS) spectra of Eu³⁺ ions and gold colloid containing Eu³⁺ were measured. For solution

Full text of DOI:10.1016/j.saa.2004.11.018

Spectrochimica Acta Part A 61 (2005) 3002–3005
3
+
Resonance light scattering properties of Eu in gold colloid
Zhu Jian , Zhu Xiangb
a,∗
a
School of Science, Xi’an Jiaotong University, Xi’an 710049, China
Department of Pathology, Peking University, Beijing 100871, China
b
Received 11 August 2004; accepted 10 November 2004
Abstract
Gold colloidal containing rare-earth ions Eu were prepared at room temperature. Fluorescence spectra and resonance light scattering
3
+
3
+
3+
3+
(
RLS) spectra of Eu ions and gold colloid containing Eu were measured. For solution containing Eu , RLS features show two peaks at
the edges of the visible light wavelength region. The short wavelength peak takes place at about 400 nm and the longer wavelength peak is the
corresponding 1/2 fraction frequency RLS peak, which takes place at about 780 nm. When gold colloids were added to the solution containing
3
+
Eu , both these two RLS peaks were enhanced. We believe that the energies, which are absorbed by the surface plasmon resonance in the
3
+
gold nanoparticles, are efficiently transferred into the Eu ions to cause the increased scattering.
2004 Elsevier B.V. All rights reserved.
©
PACS: 78.67.Bf; 73.20.Mf; 36.40.Gk
Keywords: Resonance light scattering; Gold colloid; Europium ions; Surface plasmon resonance; Local field
diameter were precipitated to dope the Eu3+ ions. In the pa-
per of Magyar et al. [5], chelation of rare-earth (RE) ions is
investigated as a means of enhancing the optical properties of
RE-doped silica sol–gels. Two chelating agents 2,6-pyridine-
dicarboxylic acid (PDC) and 3-pyridinepropionic acid (PPA)
and two different synthesis techniques are studied. Eu (PDC)
gels exhibit intense D0– F2 fluorescence in the red under
UV excitation and long fluorescence lifetimes compared to
Eu (PPA) gels and to gels without a chelating agent.
The physical and chemical characteristics of colloid gold
appear most attractive because of their special electromag-
netic modes such as surface modes and local field. Surface
plasmons are collective electromagnetic oscillations at metal-
lic surfaces. It is widely accepted that for optical processes
the primary role of the roughness in metals or the small size
of noble metal particles is to enhance the local optical fields
via localized plasmon resonance, and thus improve the effi-
ciency of light absorption and emission [11–13]. Hayakawa
et al. [8] have described the increase of europium ion fluores-
cence owing to resonant plasma oscillation of silver particles
in silica glass, which were precipitated by annealing in a
reducing atmosphere sol–gel-derived SiO2 glass containing
1
. Introduction
Rare-earth ions such as Eu3+ and Dy3+ in different host
material are of current interest because of their special
electronic and optical properties and potential applications
[1–10]. In the paper of Dejneka et al. [2], red, green, blue and
3+
5
7
novel UV fluorescence have been observed in Eu -doped
fluoride glasses. The effect of increasing Eu3+ concentration
on emission was found to decrease blue emission and in-
crease the green and red via nonradiative dipole–quadrupole
and dipole–dipole ion pair transitions. Rambabu et al. [3]
have reported the fluorescence properties of a new series
of Eu -doped powder phosphors based on GdOBr, LaOBr
and YOBr. The relative fluorescence intensity ratios for the
different measured emission levels were also evaluated in
order to examine the host matrix compositional effects on
the fluorescence behaviours. In the letter of Nogami et al.
3+
3+
[4], Eu -doped SnO2–SiO2 glasses were prepared using a
sol–gel method, where nanosized SnO2 crystals of ∼8 nm in
∗
Corresponding author. Tel.: +86 29 2672529; fax: +86 29 2668004.
E-mail address: zhujian@mail.xjtu.edu.cn (Z. Jian).
1
386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.11.018

Z. Jian, Z. Xiang / Spectrochimica Acta Part A 61 (2005) 3002–3005
3003
+
3+
Ag and Eu ions. They have come to the conclusion that the
most probable mechanism for the fluorescence increase is a
local field enhancement around Eu3+ ions, due to the induced
surface plasmon resonance of Ag particles. Nogami et al. [4]
have reported that when excited at the energy corresponding
to the absorption edge of the SnO2 nanocrystals, the SnO2-
doped glass exhibits fluorescence intensities of the Eu3+ ions
higher than 150 times that of the glass without nanocrystals.
The energies, which are absorbed by the quantum-dot effect
in the nanosized crystals, are efficiently transferred into the
3
+
Eu ions to cause the high emission.
If a solid particle is illuminated by electromagnetic wave,
electric charges in the obstacle will be set into oscillatory
motion. Accelerated electric charges radiate electromagnetic
energyinalldirections, thissecondaryradiationiscalledscat-
tering. If the wavelength of the incident beam is close to that
of the absorption band of the molecular particles, Rayleigh
scattering will deviate from the ordinary law and the intensity
of some wavelengths will rapidly increase. This phenomenon
is called resonance light scattering (RLS) [14–16]. In recent
years, RLS as a new analytical technique has been applied
to the study and determination of some biological macro-
molecules, ion-association complexes, trace amounts of met-
als, non-metals and so on [16–20]. In this paper, we study on
the resonance light scattering properties of gold colloid con-
Fig. 1. TEM image of gold colloidal nanospheres.
7
5
the D0 → F2 band at 620 nm is an electric dipole transition
3
+
and sensitive to chemical bonds in the vicinity of Eu ions
4]. So the fluorescence excitation spectra are studied in or-
der to find the sensitive excitation frequency. The excitation
spectrum in Fig. 2 is the scanning excited wavelength from
00 to 600 nm when the detection wavelength was located at
20 nm. The experimental results in Fig. 2 show that the flu-
[
2
6
orescence at 620 nm is sensitive to the excitation at 395 nm.
It is important to note that when amount of gold colloid were
3+
3+
added to the solution containing Eu , the corresponding ex-
citation peaks increase, as shown in Fig. 2.
tainingEu . TwoRLSpeaksareobservedat400and780 nm,
respectively. Enhancement of these scattering peaks has also
been observed by the addition of gold colloids. Furthermore,
we discuss in detail the mechanisms of the enhanced RLS
3+
Solution containing only Eu and solution containing
both gold nanoparticles and Eu3+ are excited at 395 nm. The
corresponding fluorescence emission spectra are compared in
from Eu3 in gold colloids.
+
3+
Fig. 3. For solution containing only Eu , five emission peaks
fixed at 535, 555, 590, 620 and 695 nm display. We believe
5
7
that these fluorescence peaks are resulted from D1 → F1,
2
. Experimental
5
7
5
7
5
7
5
7
D1 → F2, D0 → F1, D0 → F2 and D0 → F4 band
3+
transitions of the Eu , respectively [2,3]. Whereas when
amount of gold colloid were added to the solution containing
Europium oxide Eu2O3 (0.03 g) was dissolved in H2O
(25 ml, including 20% HNO3). This synthesis was conducted
3+
Eu , most of these fluorescence emission peaks increase. We
believe that these enhanced fluorescence are due to the local
under an ultrasonication at room temperature. The resul-
tant solution was transparent and has no color. Gold col-
loid nanoparticles were prepared via electrochemical method
[21,22]. The transmission electron microscopic (TEM) im-
ages are obtained by using a JEOL JEM-200CX TEM, the
gold nanoparticles with mean diameter 15 nm have been ob-
served, as shown in Fig. 1. The color of the resultant solution
was red. At last, amounts of gold colloid were added to the so-
lution containing Eu3+ with gentle mixing. Then the resultant
solution turns to light pink.
3
. Results and discussion
The fluorescence spectra are recorded on a Perkin Elmer
LS 55 spectrophotofluorometer. It is known that the fluores-
cence spectra of Eu3+ consist of a series of resolved bands
3+
Fig. 2. Fluorescence excitation spectra of solution containing only Eu and
5
7
peaking at 570–630 nm, which are assigned to D0 → Fj
3+
solution containing both gold nanoparticles and Eu (detection wavelength
5
7
(
j = 0, 1, 2, 3, 4)transitions. Amongthe D0 → Fj transitions,
is 620 nm).

3
004
Z. Jian, Z. Xiang / Spectrochimica Acta Part A 61 (2005) 3002–3005
ions. It is interesting to note that the scattering enhance-
ment at 780 nm is more intensive than that at 400 nm. This
result indicates that the increase of 1/2 fraction frequency
RLS peak is more sensitive to the addition of gold nanoparti-
cles.
It is well known that the scattering is essentially the re-
radiation from the accelerated electric charges. When the in-
cident beam is close to that of the absorption band of the
molecular particles, the RLS will takes place. The excitation
peak fixed at 395 nm in Fig. 2 shows that the fluorescence
from Eu3+ is sensitive to the excitation at 395 nm. Further-
more, inRef. [4], theabsorptionbandduetothef–ftransitions
of the Eu3+ ions was observed at 395 nm. So we believe that
this resonance scattering peak fixed at about 400 nm in Fig. 4
is attributed to the coupling between the excitation light and
3
+
3
+
the absorption band of Eu .
Fig. 3. Fluorescence emission spectra of solution containing only Eu and
3
+
solution containing both gold nanoparticles and Eu (exciting at 395 nm).
When gold colloids were added to the solution contain-
3+
3+
ing Eu , the environment of Eu has changed and the gold
nanoparticles play an important role. Excitation of the gold
nanoparticles at 400 nm leads to excitation of the surface plas-
mon coherent electronic motion. According to the theoretical
research of the photo-induced luminescence [24], both the in-
coming and outgoing fields are propose to be enhanced via
coupling to the local plasmon resonance. The dependence of
the Eu3+ radiation intensity on the gold nanoparticles sug-
gests the energy transfer from the nanoparticles to Eu .
When Eu3+ ions in the solution adsorb on the surface of gold
nanoparticles, the energy of collective electromagnetic oscil-
lations at gold surfaces will transfer from gold nanoparticles
to Eu3+ ions [25]. So the enhanced oscillatory of the electric
charges results in the enhanced secondary radiation and the
increased scattering.
field enhancement around Eu3+ ions owing to the induced
surface plasmon resonance of gold nanoparticles and energy
transfer from gold nanoparticles to Eu3+ ions.
The RLS spectrum is the spectrum that showed the ex-
cited and emission wavelengths synchronously in the form
of ꢀλ = 0 (λex = λem) [16]. Fixed the detection wavelength
equal to the excitation wavelength, we get the intensity of
scattering light. Compared the relative intensity of the scat-
tering peaks with different excited wavelengths, we find that
the resonance light scattering are intense from 380 to 480 nm
and the strongest peak is at about 400 nm. Furthermore, the
corresponding 1/2 fraction frequency RLS peak at 780 nm is
also observed, as shown in Fig. 4. This nonlinear scattering
phenomenon could be illustrated from the pump effect and
theory of quanta optics [16,23]. It is important to note that
when amount of gold colloid were added to the solution con-
3
+
3+
4. Conclusion
taining Eu , both these two RLS peaks increase, as shown
in Fig. 4. The solution containing both gold colloid and Eu3+
exhibits RLS intensities higher than 1.5 times at 400 nm and
Fluorescence and RLS characters of solution containing
Eu3+ have been studied at room temperature. Two resonance
light scattering peaks are observed at 400 and 780 nm, respec-
tively. Both these two scattering peaks are enhanced when
amount of gold colloid are added to the solution contain-
ing Eu . We believe that the scattering peak fixed at about
00 nm is attributed to the coupling between the excitation
light and the absorption band of Eu . Furthermore, the en-
hancement of the scattering is due to the energy transfer from
the local field in gold nanoparticles to Eu3+ ions.
.5 times at 780 nm that of solution containing only Eu3+
7
3+
4
3+
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