Supplementary Material
Energy transfer from pyridine molecules towards Europium cations contained in
sub 5-nm Eu2O3 nanoparticles: can a particle be an efficient multiple donoracceptor system?
I.
Schematic representation (Fig. 1) of each step of the elaboration process of coreshell particles grafted with pyridine molecules (antenna).
Figure 1. Schematic presentation of the synthesis process
II.
High-resolution transmission electron microscopy (HRTEM) images performed
on core/shell particles
a)
b)
Figure 2. a) High resolution TEM image of Eu2O3 core nanoparticles showed the
crystallised phase. b) Fast Fourier Transform (FFT) of some crystallised oxide and their
interreticular distances. The interreticular distances and the angles observed fit the bcc
lattice parameters with a = 10.86 ± 0.01 Å.
a)
Number of cores (arb. units)
b)
TEM observations
DLS measurements
1
10
Hydrodynamic diameter of the cores (nm)
Figure 3. a) High resolution TEM image of Eu2O3 nanoparticles coated by polysiloxane.
Polysiloxane shell is not visible on the images and reduces the visualization of the
fringes related to the crystallised oxide. b) Comparison between the size distributions of
cores by TEM analysis and by DLS measurements.
III.
Characteristic of synthesis steps: table 1, the amount of pyridine molecules (the
donors) per particle is varied; table 2 the polysiloxane thickness of the particle is varied.
Number of antenna grafted on the core/shell particles
2,6-Pyridinedicarboxylic acid
Number of Antenna per
europium atom
Europium amount (µmoles)
APTES (µL)
TEOS (µL)
DEG solution (µL)
Antenna (µg)
EDC (µg)
NHS (µg)
1/250
1/100
1/20
1/10
0.2
0.4
0.6
0.8
1.2
60
16.8
10.8
40.8
40.0
92.0
55.2
60
16.8
10.8
40.8
100.0
230.0
138.1
60
16.8
10.8
40.8
500.0
1150.2
690.5
60
16.8
10.8
40.8
1000.0
2300.4
1381.1
60
16.8
10.8
40.8
2000.0
4600.8
2762.2
60
16.8
10.8
40.8
4000.0
9201.6
5524.3
60
16.8
10.8
40.8
6000.0
13802.4
8286.5
60
16.8
10.8
40.8
8000.0
18403.2
11048.6
60
16.8
10.8
40.8
12000.0
27604.8
16572.9
Table 1. Different amount of pyridine molecules for the same thickness of polysiloxane
Number of silica shell coating the oxide core with the amount of antenna graft on the surface
2,6-Pyridinedicarboxylic acid
Number of Silica per europium
atom
Europium amount (µmoles)
APTES (µL)
TEOS (µL)
DEG solution (µL)
Antenna (mg)
EDC (mg)
NHS (mg)
1 Si
2 Si
3 Si
4 Si
600
84
54
204
0.40
0.92
0.6
600
168
108
408
0.40
0.92
0.6
600
252
162
612
0.40
0.92
0.6
600
336
216
816
0.40
0.92
0.6
Table 2. Different amount of APTES/TEOS precursors for the number of Antenna
𝐷
𝐴
𝑛
𝐷
𝐷
= 𝑛 𝑝𝑦𝑟𝑖𝑑𝑖𝑛𝑒/𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 ⇔ 𝑛𝑝𝑦𝑟𝑖𝑑𝑖𝑛𝑒/𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 = 𝑛𝐸𝑢/𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝐴 = 670 𝐴.
𝐸𝑢𝑟𝑜𝑝𝑖𝑢𝑚/𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
IV.
Calculation of the silica thickness by ICP-AES analysis and comparison with the silica
thickness measured by DLS analysis
After ultrafiltration of the colloidal samples (3 kDa PES membrane), an ICP – AES was
performed in order to obtain the number of Silicon and Europium atoms amount for each
sample. It is then possible to calculate the yield of oxide formation rEu and the polysiloxane
coating rSi. The amount of Europium was found the same even after purification. Thus rEu was
determined equal to 1.
The volume ratio of the silica and Europium in each sample was calculated in function of r Si
and rEu:
𝑉𝑆𝑖𝑂2
𝑟𝑆𝑖 𝑀𝑆𝑖𝑂2 ⁄𝑑𝑆𝑖𝑂2
= 𝑛
𝑉𝐸𝑢01.5
𝑟𝐸𝑢 𝑀𝐸𝑢𝑂1.5 ⁄𝑑𝐸𝑢𝑂1.5
with n the ratio of SiO2 and EuO1.5 introduced, 𝑀𝑆𝑖𝑂2 (60.1 g.mol-1) and 𝑀𝐸𝑢𝑂1.5 (175.9 g.mol-1)
the molecular mass of SiO2 and EuO1.5 respectively, 𝑑𝑆𝑖𝑂2 (2) and 𝑑𝐸𝑢𝑂1.5 (7.5) the density of
SiO2 and EuO1.5 respectively.
Direct estimation of core size by TEM micrographs analysis (Rcore = 1.8 nm) and the
knowledge of the polysiloxane to the Europium volume ratio, allows the calculation of
polysiloxane thickness e of nanoparticles:
𝑉𝑆𝑖𝑂2
𝑉𝐸𝑢01.5
=𝑛
(𝑅+𝑒)3 −(𝑅)3
(𝑅)3
3
𝑒 = √
𝑀𝑆𝑖𝑂
2
𝑟𝑆𝑖 𝑑
𝑆𝑖𝑂2
(𝑅𝑐𝑜𝑟𝑒 )3 +(𝑅𝑐𝑜𝑟𝑒 )3
𝑀𝐸𝑢 𝑂
𝑛2𝑑 2 3
𝐸𝑢2 𝑂3
– 𝑅𝑐𝑜𝑟𝑒
n
rSi
𝑉𝑆𝑖𝑂2
𝑉𝐸𝑢01.5
Calculated
Thickness (nm)
Measured
Thickness (nm)
1
0.41
0.52
0.27
0.28
2
0.36
0.92
0.43
0.44
3
0.35
1.34
0.59
0.6
4
0.33
1.69
0.70
0.71
Table SI: comparison between calculated thickness and measured thickness by DLS analysis
1.0
ThicknessSi shell (nm)
Calculated from the yield of Si coating
Measured from DLS
0.8
0.6
0.4
0.2
0.0
1
2
3
4
Number of polysiloxane addition
The thickness of polysiloxane shell determined by ICP analysis or measured by DLS is almost
the same.
V.
Luminescence spectra of, on one hand the core alone and, on the other hand,
the four core/shells elaborated.
140
Eu2O3
Iemi
@ exci = 395 nm
(arb. units)
120
Eu(OH)
Eu2O3@1Si
100
Eu2O3@2Si
Eu2O3@3Si
80
Eu2O3@4Si
60
40
20
0
550
600
650
700
750
Wavelength (nm)
Figure 4. Comparison of Europium’s emission spectra for an excitation at 395 nm
between on one hand the particles with the different thicknesses and the particles
without polysiloxane shell, and the other hand, the hydroxide europium particles.
1- The comparison of the 5D0  7F1 magnetic and of the 5D0  7F2 forced electric
dipole transition related to the spectrum of the core demonstrates that this latter
effectively possesses the bcc oxide phase. Indeed, the hydroxide phase is
characterized by an electric transition largely smaller than that of the magnetic
one.
2- By polysiloxane coating the electric transition band increases. This is in
agreement with the modification of the Eu cations at the vicinity of surface
coating.
3- The increase in the electric transition is the same regardless of the quantity of
polysiloxane deposited on the core. This indicates that, from the first shell
growth, the surface of the core is entirely coated. This constitutes a major
agreement for a uniform and homogeneous coating.
VI.
Emission spectra for an excitation at 340 nm of: free pyridine molecules,
pyridine grafted on Eu2O3 + 0.44 nm SiOx, pyridine grafted on Eu2O3 + 0.28
nm SiOx. For each case, the pyridine concentration was 78 molecules per µm3
and the Europium concentration was 29 particles per µm3. There is an
expected emission reduction of the pyridine luminescence due to the transfer.
Pyridine alone
Eu2O3@0.44 nm SiOx@pyridine
Iem (arb.units)
Eu2O3@0.28 nm SiOx@pyridine
375
400
425 450 475
Wavelength (nm)
500
525
Figure 5. Comparison of the emission spectra for an excitation at 340 nm between the
free pyridine molecules, the pyridine grafted on the europium oxide core with 0.44 nm SiOx, and with 0.28 nm - SiOx.