Luminescent CeCl3 nanoparticles by Tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)cerium diglyme photolysis in chlorinated solvents

Article abstract of DOI:10.1016/j.ica.2006.05.022

Irradiation of [Ce(hfac)₃(diglyme)] (hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato and diglyme (DG) = 2,5,8,11,14-pentaoxapentadecane) in chlorinated solvents (CH₂Cl₂, CCl₄) with UV light led to luminescent colloidal CeCl₃ that was characterized by transmission electron microscopy (TEM) analysis. When a substrate, quartz or silicon was present in the reaction cell, photoluminescent films were obtained, containing either pure CeCl₃ or mixtures of CeCl₃, CeF₃ and CeOx in function of the experimental parameters of irradiation. Nanostructured and luminescent pure CeCl₃ films were obtained by irradiation of the cerium complex in CCl₄ at high intensity light for a few minutes. The films were characterized by X-ray diffraction (XRD), Energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), TEM, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kinetics of the [Ce(hfac)₃(diglyme)] solution photodegradation, followed by UV spectrophotometry and spectrofluorimetry, pointed to CeCl₃ formation by a solvent-initiated reaction, whereas the other inorganic compounds were the products of side reactions.

Full text of DOI:10.1016/j.ica.2006.05.022

Inorganica Chimica Acta 359 (2006) 4043–4052
www.elsevier.com/locate/ica
Luminescent CeCl3 nanoparticles by
Tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)cerium
diglyme photolysis in chlorinated solvents
a,
a
a
Salvatore Giuffrida *, Guglielmo G. Condorelli , Lucia L. Costanzo ,
Giorgio Ventimiglia a,b, Maria Favazza , Salvatore Petralia , Ignazio L. Fragala
a
a,b
a
`
a
`
Dipartimento di Scienze Chimiche, Universita degli Studi di Catania and INSTM UdR di Catania, V.le A. Doria 6, 95025 Catania, CT, Italy
b
LoC R&D, Microfluidic Division-CPG ST Microelectronics, I-95121, Catania, Italy
Received 9 March 2006; received in revised form 2 May 2006; accepted 13 May 2006
Available online 2 June 2006
Abstract
Irradiation of [Ce(hfac)3(diglyme)] (hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato and diglyme (DG) = 2,5,8,11,14-pentaoxapen-
tadecane) in chlorinated solvents (CH2Cl2, CCl4) with UV light led to luminescent colloidal CeCl3 that was characterized by transmission
electron microscopy (TEM) analysis. When a substrate, quartz or silicon was present in the reaction cell, photoluminescent films were
obtained, containing either pure CeCl3 or mixtures of CeCl3, CeF3 and CeOx in function of the experimental parameters of irradiation.
Nanostructured and luminescent pure CeCl3 films were obtained by irradiation of the cerium complex in CCl4 at high intensity light for a
few minutes. The films were characterized by X-ray diffraction (XRD), Energy dispersive X-ray (EDX), X-ray photoelectron spectros-
copy (XPS), TEM, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kinetics of the [Ce(hfac)3(diglyme)]
solution photodegradation, followed by UV spectrophotometry and spectrofluorimetry, pointed to CeCl3 formation by a solvent-initi-
ated reaction, whereas the other inorganic compounds were the products of side reactions.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Photochemistry; Luminescence; Nanoparticles; Deposition; Cerium chloride
1. Introduction
In general, these luminescent ions are used as dopants
for second group metal halide host matrices. Studies on
Ce3+ luminescence properties in alkaline earth (Ca, Sr,
Ba) chlorides [4] showed that the energy shift of the emis-
sion depends on the structure of the host lattice. Moreover,
it has been proven that the particles at the nanometer level
have an improved quality with respect to their potential
application to various optical, electrical, mechanical and
catalytic activities [5]. It is known that the dimensions of
phosphor particles are crucial in the enhancement of the
luminescence [6,7]. Many techniques have been used to pre-
pare thin films of cerium-containing materials, such as
evaporation methods, sputtering, spray pyrolysis technique
[8], whereas only a CVD technique has been reported to
obtain pure cerium fluoride films [9]. To the best of our
knowledge, nowadays no method has been reported in
In the last decade, a great interest has been shown in tri-
valent lanthanide rare-earth ions, such as cerium(III),
because of their luminescence properties. These ions are
involved in the fabrication of electroluminescent [1] and
photoluminescent [2,3] devices. They could be used in pro-
jecting new solid-state lasers in the ultraviolet and blue
spectral domains. The emission from such types of ions is
strictly connected with the host crystal. Thus, rare earth
activated luminescent materials have been studied in their
crystalline and powder form for use in cathodic ray tube
(CRT) phosphors and other related applications.
*
Corresponding author. Tel.: +39 0957385063; fax: +39 095580138.
E-mail address: sgiuffrida@unict.it (S. Giuffrida).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.05.022

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S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
the literature to obtain pure films of CeCl3. In this paper,
we report about the fabrication of colloidal particles and
nanostructured films of pure CeCl3 by using a simple and
inexpensive method of photochemical deposition from
liquid phase [10,11].
stances, such as free ligand or decomposition organic prod-
ucts, adsorbed on the surface.
Some CeCl3 deposition, depending upon the starting
complex concentration, occurred on the interior walls of
the cuvette. However, this did not prevent the light from
attaining the solution bulk.
2. Experimental
For the chemical characterization of the colloidal parti-
cles, a deposit was obtained upon solvent evaporation, on
suitable substrate, of some drops of the colloidal solution.
XPS measurements were performed with a PHI 5600
Multy Technique System equipped with an Al standard
X-ray source operating at 14 kV and a hemispherical ana-
lyzer. The electron take off angle was 45ꢁ. Binding energy
(BE) data were calibrated on C 1s at 285 eV.
[Ce(hfac)3(diglyme)] was synthesized according to the
literature [12]. CH2Cl2 and CCl4 were of analytical grade
with H2O of about 0.02% or 0.01%, respectively. Warning:
CCl4 is toxic for inhalation and dangerous for ozone layer.
CeCl3 commercial anhydrous powder was purchased
from Aldrich.
Irradiation was performed with cuvettes of optical path
of 1 cm, whereas the measurements were carried out with
cuvettes of optical path 0.1, 0.5 or 1 cm, depending on
the concentration of the solution.
For light source, a Rayonet photochemical reactor,
equipped with a variable number of lamps (Italquartz) with
monochromatic emission at either 254 nm or at 300 nm,
was used. The light intensity, measured by a ferric oxalate
actinometer [13], was in the range of 1.08–27 mW cmꢀ2
XRD measurements were made with a Bruker AXS
D5005 X-ray diffractometer.
Chemical composition of film and powders was evalu-
ated by EDX analysis using a windowless IXRF solid state
detector and the surface morphology was examined
through scanning electron microscopy (SEM) using a
LEO SUPRA 55VP equipped with a field emission gun.
AFM images were acquired with a microscope SOLVER-
Pro by Nt-MDT.
TEM images of cerium chloride nanoparticles were
obtained by means of a FEG JEM 2010F instrument with
a field emission gun operating at 200 kV. The electro-optical
configuration guarantees ultra high spatial resolution
(0.19 nm). This microscope is equipped with the GIF (Gatan
Image Filter) apparatus, which allows realizing images fil-
tered to narrow windows of the electron energy loss
spectrum.
(4.0 · 10ꢀ7–1.0 · 10ꢀ5 Nhm minꢀ1
)
for
254 nm
and
6 mW cmꢀ2 (2.6 · 10ꢀ6 Nhm minꢀ1) for 300 nm. When nec-
essary, a screen with a suitable window was used.
The quantum yields were calculated by ratio between
initial disappearance rate of the complex and number of
absorbed photons by reactive species.
UV–Vis absorption spectra were measured using a dou-
ble beam Jasco-V560 spectrophotometer.
For the luminescence spectra, a SPEX Fluorolog 111
instrument, equipped with a solid sample holder, was used.
The luminescence spectra are recorded within the linear
range of the photo multiplier response.
3. Results and discussion
Films were obtained on quartz and Si(100) substrates of
dimensions 0.5 · 2 cm, using solutions of concentration
10ꢀ3 mol Lꢀ1 in CCl4. To obtain substrates with just one
side covered, the quartz plate was deposited on the bottom
of an horizontally disposed cuvette and irradiated from
below with a single lamp; whereas to cover both sides,
the substrate (silicon or quartz) was put along the diagonal
of the cuvette and irradiated into the photochemical reac-
tor (Fig. 1).
3.1. Photolysis of [Ce(hfac)3(diglyme)] in chlorinated
solvents
Preliminary experiments regarding the photochemical
reactivity of [Ce(hfac)3(diglyme)] at UV light showed that
in the non-chlorinated solvents, such as methanol and ace-
tonitrile, the complex can be considered photochemically
inert, because it underwent slow degradation with quantum
yield <10ꢀ4. In the chlorinated solvents, like CH2Cl2 and
CCl4, photolysis occurred, leading mainly to colloidal cer-
ium chloride. When a substrate was present in the reaction
cell, luminescent films containing CeCl3 were obtained.
The photoreaction kinetics were followed by spectro-
photometric and fluorimetric analysis. In both solvents,
the electronic spectrum of [Ce(hfac)3(diglyme)] exhibits a
band due to the intra-ligands pL to pꢁL transitions (IL)
(kmax = 306 nm and 308 nm, molar absorptivity
(e) = 28000 L molꢀ1 cmꢀ1 and 30000 L molꢀ1 cmꢀ1 in
CH2Cl2 and in CCl4, respectively), as found in other com-
plexes with betadiketonate ligands [14,15]. A shoulder, due
to cerium(III) ion electronic transitions (5d–4f), is present
at about 280 nm. The absorption of the free ligand in the
After photochemical film deposition, the substrates were
washed with pure solvent to remove possible organic sub-
Fig. 1. Cuvettes for CeCl3 film deposition: (a) on both sides of quartz or
silicon substrates; (b) on just one side of quartz substrate.

S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
4045
protonated form is centred at 274 nm (e = 6700 L molꢀ1
cmꢀ1) in both solvents.
The irradiation of [Ce(hfac)3(diglyme)] solutions pro-
voked spectral changes showing the bleaching of the absor-
bance maximum and the growth of a band at 274 nm, this
latter being typical of the protonated ligand Hhfac (Fig. 2).
The isosbetic point at about 290 nm proved that the pro-
cess was occurring with constant stoichiometry without
side reactions. With the naked eye the irradiated solutions
appeared clear, but a diffuse absorbance above 350 nm,
that was better observed as the complex concentration
increased, indicated the presence of colloidal particles
and the formation of a slight deposit on the inner walls
of the cuvette.
As the absorbance maximum decreased, the characteris-
tic emission of the CeCl3 [16,17] appeared and increased
with reaction time (Fig. 3). This emission exhibited high
maxima at 355 nm and at 370 nm, which were shifted
about 12 nm towards the visible region with respect to
the luminescence, recorded with commercial CeCl3 powder,
dispersed in CCl4.
Fig. 3. Emission spectra (kexc = 300 nm) of CeCl3 colloidal particles in
CCl4, formed at 254 nm, at various irradiation times (tirr = 45 s). In the
inset: commercial CeCl3 powder dissolved in CCl4.
Prolonged irradiation provoked slow decomposition of
the released ligand, detectable by a decrease of the absor-
bance at 274 nm and a shift of the isosbestic point.
These findings allowed us to deduce that the following
photochemical reaction occurred:
When solutions of concentration higher than
3 · 10ꢀ4 mol Lꢀ1 were irradiated, decomposition of the
released ligands occurred before the complete photolysis
of the complex. The films obtained in these conditions con-
tained chloride, fluoride and oxide of cerium (see below).
The kinetics of the photodegradation at 254 nm were
investigated in function of the initial complex concentration
and incident light intensity. The results showed that the
absorbance maximum of the complex (thus its concentra-
tion) decreased linearly with irradiation time (Fig. 4) for
most of the reaction. This indicated kinetics of zero order
and a constant rate of reaction, evaluated as ꢀd[complex]/
dt. Besides this, by increasing the solution concentration,
the plot slopes (thus the reaction rate) decreased in CH2Cl2,
whereas it remained constant in CCl4. For the solutions
reported in Fig. 4a, the rate values are 7.2 · 10ꢀ6, 4 · 10ꢀ6
and 1.5 · 10ꢀ6 mol Lꢀ1 minꢀ1 from bottom to top; for the
UV light
½CeðhfacÞ ðdiglymeÞꢂ
CeCl þ 3Hhfac þ diglyme
ƒƒƒƒƒ!
3
3
CH2Cl2;CCl4
Because Hhfac and diglyme are quite soluble in chlorinated
solvents, the colloidal particles were constituted of the
CeCl3 as confirmed by XPS results which are discussed
later in this paper.
For 254 nm irradiation of solutions of concentrations
less than 3 · 10ꢀ4 mol Lꢀ1, at all times of irradiation the
free ligand concentration was three times more than the
disappeared complex concentration (ꢀD[complex] = 1/
3D[ligand]). The isosbestic point remained constant, until
the complete release of the ligands; thus the substitution
hfacꢀ with Clꢀ occurred without any side reaction. The
films obtained in these conditions were constituted only
by CeCl3 (see below).
Fig. 2. Spectral changes of [Ce(hfac)3(diglyme)] (3.5 · 10ꢀ5 M) at various irradiation times. kexc = 254 nm. I = 5.4 mW cmꢀ2: (a) CH2Cl2 (tirr = 3 min); (b)
CCl4 (tirr = 45 s).

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S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
Fig. 4. Change of the complex concentration vs. the irradiation time. kexc = 254 nm. (a) CH2Cl2, I = 5.4 mW cmꢀ2; (b) CCl4, I = 1.08 mW cmꢀ2
.
solutions reported in Fig. 4b, the rate value is
1.5 · 10ꢀ5 mol Lꢀ1 minꢀ1 in all cases.
h
CH2Cl2
CH2Cl + Cl
(1)
(2)
(3)
At constant concentration, the rate reaction increased
linearly with the light intensity in the range 4 · 10ꢀ7
–
CH2Cl2 + Cl
HCl + CHCl2
2 · 10ꢀ6 Nhm minꢀ1 (1.08–5.4 mW cmꢀ2) in both solvents
(Fig. 5).
CH2Cl + CH2Cl2
CH3Cl + CHCl2
The photochemical behaviour of the cerium complex is
typical of a solvent-initiated reaction, whose rate depends
on the fraction of light absorbed by the solvent; thus it
decreases with the complex concentration. The literature
contains examples of such types of solvent-initiated reac-
tions for chlorinated solvents [18], in which the solvent
absorbs the UV light to give homolytic cleavage of C–Cl
bond with production of chlorinated radicals leading to
HCl and subsequent ligand substitution.
In the present case, this assertion was confirmed by suit-
able experiments showing that the preirradiated solvent
was able to provoke ligand substitution with chloride ion
in the complex, which was added subsequently.
Scheme 1.
reaction can occur both because it is a chain reaction that
requires very little light input and because the wavelength
distribution of the light source can provide some flux of
light below 254 nm. The observed decrease of the reaction
rate with concentration of complex is due to the increase of
the 254 nm absorbance of the latter, with consequent
decrease of the light fraction absorbed by the solvent.
The CH2Cl2 provides HCl, which undergoes Clꢀ–hfacꢀ
substitution, according to Scheme 1, proposed previously
[19].
In the presence of oxygen the CHClÅ2 radical undergoes
decomposition leading, through a complex mechanism, to
the following reaction:
In dichloromethane, only 2.5% of the 254 nm light is
absorbed by the solvent. Nevertheless, a solvent-initiated
O2
CHClÅ2 ! CO þ HCl þ other products
ð4Þ
Further confirmation of the proposed mechanism was pro-
vided by some experiments showing the role of oxygen in
the process. It was found that by lessening the dissolved
oxygen in solution by means of nitrogen bubbling, the
complex degradation rate decreased with the time of
deaeration.
The linearity of the dependence of the rate reaction on
the light intensity is in accordance with a mechanism
involving radical termination steps, which do not affect
the rate [20].
The quantum yield of CeCl3 formation, calculated by
values of the rate and of light fraction absorbed only by
dichloromethane, is UCH Cl ¼ 0:47.
2
2
As regarding the CCl4, earlier investigations [21,22] have
evidenced that the direct and sensitised photolysis of CCl4
leads to ClÅ and CCl3Å radicals. The radical CClÅ3 leads to
Fig. 5. Reaction rate as a function of incident light intensity. [com-
plex] = 3 · 10ꢀ5 mol Lꢀ1, kexc = 254 nm. (a) CH2Cl2; (b) CCl4.

S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
4047
HCl through several microreactions, including the forma-
ations of shorter wavelengths which are responsible for the
photoreaction.
tion of CCl3OÅ and COCl2 intermediates.
2
In the presence of H2O traces, the phosgene undergoes
hydrolysis to HCl (Scheme 2).
For a useful comparison, the rate values of complex deg-
radation are reported in Table 1.
The proposed mechanism has been confirmed by further
experiments carried out in deaerated CCl4 solution (by vac-
uum-nitrogen line). In these conditions, the degradation
complex was completely stopped suggesting that the CCl3Å
and ClÅ radicals are inactive chlorinating agents in this case.
Since the radiation of 254 nm can be considered totally
absorbed by CCl4, the rate reaction is independent of com-
plex concentration. The quantum yield, calculated by the
3.2. Chemical and morphological characterization of
deposited films and colloidal nanoparticles
Films on quartz and silicon substrates and colloidal par-
ticles have been obtained by irradiating either CH2Cl2 or
CCl4 solutions of the [Ce(hfac)3(diglyme)] at 254 nm, at
which wavelength the photodegradation rate of the com-
plex was much higher than at 300 nm (Table 1).
XRD analysis of colloidal particles and films obtained
after a short irradiation time, just to allow the release of
ligands without their decomposition (see above), indicated
that the deposit is either amorphous or with grain sizes too
small to give significant diffraction peaks. Thus, no useful
information about composition of the deposit was given
by X-ray diffraction investigation.
The nature of the deposit was, therefore, investigated by
XPS analysis. High resolution XPS spectra in the relevant
regions of binding energy (BE) are shown in Fig. 6 for both
films and colloidal particles. In both cases, the Ce 3d fea-
ture (Fig. 6a) shows a complex structure consisting of a
main Ce 3d5/2–Ce 3d3/2 spin–orbit doublet (around
886.6 eV and 905.4 eV, respectively). These BEs are consis-
tent with the presence of Ce3+ ion of CeCl3 [27] compound.
Note that each Ce 3d spin–orbit component consists of two
features due to a ground state (GS) 3d5/2–3d3/2 photoemis-
sion and a lower BE shoulder due to a charge transfer (CT)
photoemission [27,28].
The BE values of the Cl 2p3/2–1/2 spin–orbit doublet
(198.7 eV and 200.4 eV) are consistent with the presence
of CeCl3. A slight contamination of organic fluorine
(BE = 689 eV) was also observed, but no significant inor-
ganic fluorides (at about 685 eV) were detected. The O 1s
region shows a band at 532.5 eV associated with oxygen
bonded to Si in SiO2 of the substrate [29].
reaction rate and the light intensity, is UCCl ¼ 0:11.
4
For irradiation at 300 nm, a wavelength not absorbed
by dichloromethane, substitution hfacꢀ–Clꢀ, can occur
through a different pathway, involving a complex initiated
and solvent assisted reaction. This pathway involves the
interaction between the excited IL states of the complex
and the chlorinated solvent. The excited state of the ligand
could transfer an electron [23,24] to the chlorinated sol-
vent, which manifests the capability to accept an electron
[25,26], according to Scheme 3.
The electron transfer leads to chloride anion that can
bond with the positive fragment of cerium and produce
CeCl(hfac)2. The radical hfacÅ abstracts hydrogen from
the solvent, giving the ligand Hhfac and the radical
CHClÅ . Both CHClÅ and CH2ClÅ (Scheme 3) lead to HCl
2
2
according to Scheme 1. The quantum yield at 300 nm,
based on the light absorbed only by complex, is very small.
Its value is 2 · 10ꢀ4
.
As regarding the CCl4, CeCl3 formation occurred with
preirradiated solvent both at 254 and 300 nm; thus the pro-
cess was solvent initiated at both wavelengths. The mono-
chromatic radiation of 300 nm is not absorbed by the CCl4,
but the commercial lamps contain little percentage of radi-
h
CCl3
O2
Cl
+
CCl4
Quenching
CCl3O2
COCl2 + ClO
H2O
Table 1
Rate values (mol Lꢀ1 minꢀ1) of [Ce(hfac)3(diglyme)] photodegradation
Solvent
k254 (nm)
k300 (nm)
CH2Cl2
CCl4
7.2 · 10ꢀ6
1.3 · 10ꢀ7
2.5 · 10ꢀ5
1 · 10ꢀ6
CO2 + HCl
[complex] = 3 · 10ꢀ5 mol Lꢀ1;I254 = 5.4 mW cmꢀ2; I300 = 5.75 mW cmꢀ2
.
Scheme 2.
electron transfer to solvent
-
[Ce(hfac)2+, Cl ] + hfac + CH2Cl
*
Ce(hfac)3 + CH2Cl2
[CeCl(hfac)2 ]
Scheme 3.

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S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
electron transfer to solvent
-
[Ce(hfac)2+, Cl ] + hfac + CH2Cl
*
Ce(hfac)3 + CH2Cl2
[CeCl(hfac)2 ]
Fig. 6. High resolution photoemission (a) Ce 3d, (b) Cl 2p, (c) F 1s and (d) O 1s. Spectral regions (from bottom to top) of colloidal particles; films from
irradiated solutions, before ligand decomposition; films from irradiated solution, after ligand decomposition.

S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
4049
The films obtained by deposition from solutions, after
photodecomposition of the released ligands, consisted of
various compounds. The photoemission Ce 3d spectral
region (Fig. 6a, top) consisted of the main Ce 3d5/2–Ce
3d3/2 spin–orbit doublet typical of the Ce3+ ion, even
though the broadened shape is consistent with the presence
of more than one compound. In addition, a lower intensity
Ce 3d5/2–Ce 3d3/2 spin–orbit doublet (at 899 eV and
917 eV, respectively) is indicative of the presence of Ce4+
ion (i.e. CeO2) [28]. The BE values of the Cl 2p3/2–1/2
spin–orbit doublet (198.7 eV and 200.4 eV) and of the F
1s (685.4 eV), typical of inorganic chloride and fluoride
compounds, indicated the presence of both CeCl3 and
CeF3. The O 1s XPS region consists of two components:
cles and films obtained for short irradiation time is about
0.5 as expected for CeCl3. In the case of sample
obtained for long irradiation and, therefore, after ligand
decomposition, the Cl/Ce ratio decreases until 1.5 due to
the presence of other Ce-containing compounds (CeF3
and CeOx).
Finally, note that for all films, XPS analysis showed the
Si 2p signal of the substrate, thus indicating that substrate
surface is not fully covered and suggesting the presence of
CeCl3 islands.
The chemical nature of the bulk of deposit was deter-
mined by EDX analysis. According to surface XPS analy-
sis, the bulk of films and colloidal nanoparticles obtained
for short irradiation is made of cerium and chlorine with
a Cl/Ce atomic ratio close to 3 0.1, whilst the Cl/Ce ratio
decreases down to 1 for samples obtained for long
irradiation.
3
OSiO at 532.5 eV associated with oxygen bonded to Si in
2
SiO2 of the substrate [30] and OCeO at 530.0 eV associated
2
with the oxygen bonded to cerium in CeO2 [30].
It is worth noting that the CeF3 and CeOx compounds,
present in these films, are not formed by direct photochem-
ical reaction, starting from the excited complex states, but
are formed indirectly. The fluoride can be formed by an
attack of fluorinated fragments of the decomposed ligand
on the starting complex or its intermediates. The oxide
can derive from an attack of peroxy-radicals on the starting
complex or its derivates.
The surface Cl/Ce atomic ratios of various samples have
been determined from the intensity of XPS bands using
Wagner sensitivity factor [31] corrected for the instrument
transmission function. The Cl/Ce ratio of colloidal parti-
The surface morphology of films deposited on silicon
and quartz substrates has been examined with SEM analy-
sis. Fig. 7 shows SEM micrographs of films obtained under
various experimental conditions.
EDX analysis performed in points 1 indicates that the
islands are constituted by CeCl3, whilst no significant Ce
and Cl amounts have been detected for points 2.
In all cases, it results in particle aggregation with forma-
tion of islands, as already suggested by XPS results (see
above). Pointing to the islands, the performed EDX analy-
sis confirmed that they are made of CeCl3, whilst out of the
CeCl3 islands the amounts of the Ce and Cl are negligible.
Fig. 7. SEM micrographs of various films: (a) deposited on Si at high light intensity (I = 27 mW cmꢀ2, tirr = 45 s) from solutions 10ꢀ4 mol Lꢀ1; (b)
deposited on Si at high light intensity (I = 27 mW cmꢀ2, tirr = 3 min) from concentrated solution 10ꢀ3 mol Lꢀ1; (c) deposited on quartz at low light
intensity (I = 6 mW cmꢀ2, tirr = 6 h) from concentrated solution 10ꢀ3 mol Lꢀ1 and covered with Au layer for the SEM analysis; (d) deposited on Si after
ligand decomposition (I = 6 mW cmꢀ2, tirr = 12 h) from concentrated solution 10ꢀ3 mol Lꢀ1
.

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S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
Fig. 8. AFM images of pure CeCl3 films deposited from solutions 10ꢀ3 mol Lꢀ1 (a) and 10ꢀ4 mol Lꢀ1 (b–d) irradiated with light of various intensities: (a)
I = 6 mW cmꢀ2, tirr = 6 h; (b) I = 1.08 mW cmꢀ2, tirr = 8 min; (c) I = 5.4 mW cmꢀ2, tirr = 3 min; (d) I = 27 mW cmꢀ2, tirr = 45 s.

S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
4051
Fig. 9. (a) TEM analysis on a sample of colloidal CeCl3. (b) Particle size distribution.
For high light intensity (I = 27 mW cmꢀ2), but short depo-
sition times and low solution concentrations (tirr = 1 min
and 10ꢀ4 mol Lꢀ1), the films show the presence of mono-
dispersed particles with a size of about 20 nm.
not clear how much coagulation occurs in the initial solu-
tions and how much occurs during solvent evaporation
when the TEM grids are prepared. TEM image shows
the presence of nanoclusters characterized by a size distri-
bution (Fig. 9b) with an average diameter of 2.9 nm and
a dispersion r of 1.0 nm. The inset is the forward of the
Fourier transformation (FFT) of the high resolution
TEM image which shows that this sample is a fcc structure
For higher concentration (10ꢀ3 mol Lꢀ1), the particles
aggregate to form islands with sizes of some microns.
The roughness of the pure CeCl3 films obtained on
quartz has been determined by AFM measurements. The
results showed that smoother films can be obtained by
increasing the CeCl3 formation rate that can be obtained
at low solution concentration with increasing light intensity
(Fig. 8).
˚
˚
with diffraction rings at 3.17 A and 2.70 A due to the (111)
˚
and (200) planes, with a reticular parameter of a = 5.43 A.
4. Conclusion
The films obtained from solutions 10ꢀ3 mol Lꢀ1
(Fig. 8a) show the presence of islands with an average
height (Rmead) of 0.2 lm. Fig. 8b–d shows three examples
of the AFM images of CeCl3 films deposited from CCl4
solutions 10ꢀ4 mol Lꢀ1 and irradiated with increasing light
intensity. The films obtained by irradiation with a light of
lowest intensity show a rough surface (Fig. 8b) with an
average peak-to-peak distance (Rmead) of about 24 nm
and a roughness of 6.7 nm. Films obtained using light of
middle intensity show less rough surfaces (Fig. 8c). The
Rmead value is 5.4 nm with a roughness of 1.6 nm. The third
sample, obtained from solution irradiated with the highest
light intensity, shows a surface much flat and homogeneous
(Fig. 8d). The Rmead is 2.4 nm with a roughness of 0.6 nm.
Both values are significantly lower than those observed for
samples deposited by adopting less intense irradiation. It is
important to evidence that the third sample is constituted
of much smaller (40 10 nm) and more homogeneous par-
ticles, compared to those of the other two samples. This
finding supports the idea that, in general, the right tuning
of the irradiation conditions leads to the formation of
nanostructured films.
The above results evidence the close connection between
morphology, composition and grain size of nanoparticles
and films with the experimental conditions used to obtain
deposition. Luminescent films and particles of pure CeCl3
were produced by carrying out the photochemical reaction
in controlled conditions of initial concentration, of solvent
nature, of light intensity, of irradiation time, in order to
avoid photodecomposition of the released ligands, that
would bring to other inorganic compounds of cerium. By
right tuning of the cited experimental parameters, nano-
structured films of pure CeCl3 were obtained from CCl4
solutions, when the films were formed in very short irradi-
ation time; thus when the CeCl3 formation rate was very
high.
In conclusion, this paper shows that the photochemical
method was very suitable to obtain films with the desired
characteristics, by exploiting an inexpensive and simple
technique which works at room temperature. This last
characteristic can be very important, since it allows to
use several types of substrates, as functionalised substrates.
It is noteworthy to emphasize that the study of the reaction
mechanism in solution is the basis supporting all research
in the field of photodeposition from liquid phase, since
the knowledge of the photo reaction mechanism is the only
way to select the most suitable conditions to improve the
film qualities.
TEM analysis was performed on the colloidal particles
obtained by irradiating complex solution 10ꢀ3 mol Lꢀ1 in
CCl4 for 4 min. Samples have been dried on copper grids.
Fig. 9a shows TEM micrographs of the CeCl3 nanoparti-
cles forming clustered aggregates. However, note that it is

4052
S. Giuffrida et al. / Inorganica Chimica Acta 359 (2006) 4043–4052
[15] H. Nakanishi, H. Morita, S. Nagakura, Bull. Chem. Soc. Jpn. 51 (6)
Acknowledgment
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