J Nanopart Res (2010) 12:993–1002 DOI 10.1007/s11051-009-9655-5
RESEARCH PAPER
Structural and luminescence properties of europium(III)doped zirconium carbonates and silica-supported Eu3+-doped zirconium carbonate nanoparticles S. Sivestrini Æ P. Riello Æ I. Freris Æ D. Cristofori Æ F. Enrichi Æ A. Benedetti
Received: 19 January 2009 / Accepted: 4 May 2009 / Published online: 21 May 2009 Ó Springer Science+Business Media B.V. 2009
Abstract The synthesis, morphology and luminescence properties of europium(III)-doped zirconium carbonates prepared as bulk materials and as silicasupported nanoparticles with differing calcination treatments are reported. Transmission electron microscopy and X-ray diffraction analyses have, respectively, been used to study the morphology and to quantify the atomic amount of europium present in the optically active phases of the variously prepared nanomaterials. Rietveld analysis was used to quantify the constituting phases and to determinate the europium content. Silica particles with an approximate size of 30 nm were coated with 2 nm carbonate nanoparticles, prepared in situ on the surface of the silica core. Luminescence measurements revealed the role of different preparation methods and of europium-doping quantities on the optical properties observed.
S. Sivestrini P. Riello (&) I. Freris D. Cristofori A. Benedetti Dip. Chimica Fisica, Universita` Ca’ Foscari di Venezia and INSTM, via Torino 155b, 30170 Venezia-Mestre, Italy e-mail:
[email protected] F. Enrichi Civen/Nanofab, via delle Industrie 5, 30175 Venezia-Marghera, Italy
Keywords Nanoparticles Luminescence Europium doping Phosphors Silica Transmission electron microscopy
Introduction In the last decades, it has been shown that the physical and chemical properties of ultrafine particles can be modulated with their size (Alivisatos 1997; Hodes 2007). At nanometer-size, the surface to volume ratio increases dramatically, and consequently the relative magnitude of physical phenomena changes. For example, gravity becomes less important, while surface tension and Van der Waals attraction become more important. In addition, the small number of atoms or molecules within a nano-sized system often exhibit properties that can only be described by quantomechanical means. Among the variously produced nanomaterials, luminescent nanoparticles have attracted increasing technological and industrial interest. This interest is mostly due to their novel optical properties that influence emission lifetime, luminescence quantum efficiency and concentration quenching (Riello et al. 2006; Zhang et al. 1998). Recently, a substantial effort towards the synthesis of luminescent nanoparticles and subsequent physical investigations have dealt with the optical spectroscopy of rare earth (RE) doped nano-oxides (Jin et al. 1997; Jungk and Feldmann 2001; Pi et al. 2005; Speghini et al. 2005;
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Synthesis of Eu3?-doped zirconium carbonates
Khang and Van Minh 2008). The investigations and comprehension of these materials’ properties are not only of academic interest but also of technological importance for advanced phosphors, photonics and biological applications (Enrichi et al. 2008). Lanthanide oxides are usually prepared by the thermal treatment of a precursor such as an hydroxide prepared by precipitation under basic conditions, or a carbonate (or oxalate) species. Such precursors are amorphous in nature and to the best of our knowledge there are no reports in the literature which describe their optical properties. The aim of this article is to elucidate the structural and luminescence properties of europium(III)-doped zirconium carbonates, both as bulk materials and as silica-supported nanoparticles. Furthermore, one of the principal novelties of this article concerns the application of X-ray diffraction (XRD) methods, developed by some of us (Riello et al. 2008), on systems composed of amorphous phases, hence allowing us to obtain quantitative information on the synthesized systems. In order to obtain the aforementioned data, all samples were analyzed by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM) and photoluminescence (PL) techniques. A comparison between the carbonate samples and the oxides prepared via thermal treatment was also performed.
Five europium(III)-doped zirconium carbonate samples named CARBXX (where X indicates the atomic percentage of Eu in the sample) were prepared. Aqueous 10-2 M salt solutions containing 1.5 M urea were used, according to the method of Matijevic and Hsu (1987). The reaction temperature was maintained between 75 °C and 80 °C for 2 h, then cooled to ambient temperature. The solid products were decanted and centrifuged, then continuously redispersed in water and centrifuged as necessary to remove any unreacted urea. Rapid WAXS scans were used to confirm the absence of crystalline urea in the presence of the products. Table 1 indicates the reagent amounts used for the synthesis of the sample series CARBXX, and the relative concentrations of zirconium and europium atoms. A minor amount of each sample was further calcinated at 1,000 °C for 12 h to perform XRPD measurements and subsequent quantification of the europium content. Synthesis of silica-supported Eu3?-doped zirconium carbonate nanoparticles Part I: Core particles (herein referred to as CCORE) were prepared by the Sto¨ber method (Sto¨ber et al. 1968). Accordingly, distilled water (2.0 mol), ammonia (49.9 mmol), TEOS (49.9 mmol) and ethanol (449 mL) were mixed in a round-bottom flask for 48 h to provide a colloidal suspension that contained 3 g of silica. After removing the solvent under reduced pressure, the obtained humid powders were stored in a sealed container to avoid complete drying. Part II: Zirconium carbonates doped with 7, 13 and 20% europium were precipitated onto the CCORE nanoparticles in suspension to produce samples CG07, CG13 and CG20, respectively, (CGXX series). Table 2 indicates the different amounts of Eu(NO3)3 5H2O and ZrOCl2 8H2O which were added to humid
Experimental Materials Europium nitrate pentahydrate (Eu(NO3)3 5H2O, Fluka, C98.5%), zirconyl chloride octahydrate (ZrOCl2 8H2O, Sigma-Aldrich, 98%), urea (CO(NH2)2, Fluka, C99%), tetraethyl orthosilicate (TEOS, Aldrich, 98%), absolute ethanol (J. T. Baker, 99%), ammonia solution (Fluka, 28%wt in water), and distilled water. All reagents were used as received without further purification. Table 1 Reaction compositions for CARBXX series
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Sample
Zr:Eu
ZrOCl2 8H2O (mmol)
Eu(NO3)3 5H2O (mmol)
Urea (mmol)
Water (mL)
CARB00
100:0
3.0
0
608
377
CARB10
90:10
2.7
0.3
608
377
CARB15
85:15
2.6
0.4
608
377
CARB20
80:20
2.4
0.6
608
377
CARB100
0:100
0
0.6
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75
J Nanopart Res (2010) 12:993–1002 Table 2 Reaction compositions for CGXX series
995
Sample
SiO2 (mmol)
ZrOCl2 8H2O (mmol)
Eu(NO3)3 5H2O (mmol)
CG07
5.73
0.93
0.07
7
CG13
5.73
0.87
0.13
13
CG20
5.73
0.80
0.20
20
CCORE, containing 350 mg of silica suspended in distilled water (885 mL). The solutions were heated to 80 °C, followed by addition of urea (*16 g) to initiate the reaction. After 2 h, the reaction solutions were allowed to cool to ambient temperature and the obtained products were collected as powders following centrifugation. Synthesis of silica-supported Eu3?-doped zirconia nanoparticles The CGXX samples were calcinated at 700 °C for 12 h in order to convert the carbonates into the corresponding oxides, as was indicated by thermogravimetric analysis (TGA). The prepared oxides are herein referred to as CG07C, CG13C and CG20C (CGXXC series). Physical characterization XRPD patterns were collected at room temperature using a Philips X’Pert system (PW3020 vertical goniometer and PW3710 MPD control unit) equipped with a focusing graphite monochromator on the diffracted beam and with a proportional counter (PW1711/90) with electronic pulse height discrimination. A divergence slit of 0.5°, a receiving slit of 0.2 mm, an antiscatter slit of 0.5° and Ni-filtered Cu Ka radiation (30 mA, 40 kV, generating CuKa1,2 ˚ and k2 = 1.54442 A ˚) radiations at k1 = 1.54059 A were used. In order to improve the signal to noise ratio, at least three runs (collected with 10 s/step and 0.05°/step) were measured. The quantitative phase analysis for samples composed of one crystal and one amorphous phase (CGXXC series) was performed on XRPD data by applying the Rietveld method (DBWS9600 computer program written by Sakthivel and Young modified by Riello et al. (1995, 1998), using a-Al2O3 as the internal standard (IS). The Rietveld method also gave an estimated Eu3? content in the zirconia crystal lattice, since the lattice parameters are related to such concentrations. For samples composed of two amorphous phases (CGXX
Eu doping (%)
series), a method recently proposed by Riello et al. (2008) based on XRPD data was employed. TEM images were taken at 300 kV with a JEOL JEM-3010 instrument, with an ultra-high resolution pole-piece (0.17 nm point resolution), equipped with a Gatan multi-scan CCD camera (Mod. 794). The powdered samples were dispersed in isopropyl alcohol by sonication for approximately 5 min and deposited onto a holey carbon film. Energy dispersive X-ray spectroscopy (EDS) measurements were performed on a scanning electron microscope (SEM) JEOL JSM-5600LV, operated at 20 kV equipped with an Oxford Instruments ISIS series 300 EDS detector, with a polymeric atmosphere thin window allowing the detection of elements with Z [ 4 (Boron). The luminescent properties of all samples in the UV and visible regions (300–750 nm) were measured on a Fluorolog3-21 system (Horiba Jobin Yvon). A 450 W xenon arc lamp was used as a broadband excitation source and a double Czerny-Turner monochromator was used to select the excitation wavelength for photoluminescence excitation (PLE) and emission (PL) measurements. The analysis of the emitted luminescence signal from the samples was obtained by using a iHR320 single grating monochromator and a R928 Hamamatsu photomultiplier tube detector. Timeresolved characterization was obtained by exciting the sample with a SpectraLED-03 laser diode, providing 377 nm excitation with 12 nm spectral bandwidth. The excitation pulse duration was set at 5 ms and the PL decay was acquired for about 20 ms, which was sufficient to allow the signal to reach zero. These measurements were obtained by working in multi channel single photon counting (MCSPC) mode.
Results and discussion Eu3?-doped zirconium carbonates The amorphous patterns obtained by a WAXS scan in the 2h = 10° to 2h = 50° range for the Eu3?-doped
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zirconium carbonates (CARBXX) excluded the presence of urea in the sample. The formation of the carbonate species was verified by the precipitation of solid CaCO3 and the evolution of CO2, as produced by the reaction between a powdered CARBXX sample with HCl in a Ca(OH)2 solution. Considering that the stoichiometry of the prepared materials was probably not homogeneous in all the samples, especially in regards to the number of OH and CO3 groups, it is possible that different species with the formula Zr(OH)4–2x(CO3)x nZrO2 were formed. Two methods were applied for the determination of the actual Eu:Zr ratio in the prepared samples. The first method is based on determining the cell parameters of the Eu-doped zirconium oxide crystalline phase in the calcinated samples, by analysis of the peak positions in the XRD patterns. Accordingly, the amorphous carbonate powders were treated at 1,000 °C for 12 h, in order to transform to the relative crystalline oxide. Figure 1 illustrates the experimental WAXS data for sample CARB20 with the relative Rietveld fitting assuming a Eu2O3-doped cubic ZrO2 (ICSD 62456). The composition x of the solid solution EuxZr(1–x) O(2–x/2) can be obtained by using the Vegard law represented by the calibration curve, obtained on different standard samples: Vc = (133.850 ± 0.07) ? (0.223 ± 0.004)x where Vc is the cell volume of the crystalline phase (Table 3). The second method involved an EDS experiment (Table 3), which provided the relative quantities of europium and zirconium. The Eu:Zr ratios obtained using the aforementioned methods (Table 3) are in good agreement with the nominal compositions. Figure 2 illustrates the SEM micrographs of samples CARB100 (Eu-carbonate) and CARB20 (Eu–Zr-carbonate). The micrograph of CARB100 indicates the presence of carbonate spheres with submicrometer diameters in agreement with the literature (Matijevic and Hsu 1987). Contrastingly, the addition of zirconium to the system led to a change in morphology of the material that in this case is not constituted of well defined nanoparticles but of coarse powder with the grain size of hundreds of micron. The internal microstructure of these grain is shown in (Fig. 2). All the Zr containing samples show similar microstructure. The photoluminescence data for the sample series of CARBXX is shown in Fig. 3. PL spectra obtained upon irradiation with UV light (393 nm) are shown in
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Fig. 1 XRPD pattern of cubic Eu0.2Zr0.8O1.9 obtained by calcination of CARB20 at 1,000 °C for 12 h. The continuous line is the fit obtained by the Rietveld method
Fig. 3a. The room temperature emission spectra of all the samples show the typical intense spectral lines of Eu3? attributed to intra-configurational 4f ? 4f transitions, forbidden by selection rules yet partially relaxed by the interactions with the chemical surroundings. The inhomogeneous broadening of the bands is related to the amorphous nature of the samples. The ratio between the intensity of the 5D0–7F1 (580–601 nm) and the 5D0–7F2 (601–640 nm) transitions can be used as an indicative measure of the asymmetry of the coordination polyhedron of the Eu3? ion. In particular, the former transition is a pure magnetic dipole transition, impervious to the effects of the surrounding crystal field, while the latter one is a hypersensitive-forced electric dipole transition allowed only at low symmetries with no inversion centre (Reisfeld and Jorgensen 1977; Liu and Chen 2007). The asymmetric ratio, A21—can be written as R 640 IðkÞdk A21 ¼ R601 ð1Þ 601 580 IðkÞdk where I(k) is the luminescence intensity at the wavelength k, as can be measured with a spectrophotometer. A higher ratio corresponds to a lower site symmetry. Only slight differences can be appreciated amongst the PL spectra and the calculated values for A21, reported in Table 3 with the europium atomic percentage. The asymmetric ratio A21 appears to be unrelated to the europium content, and is attributed to the characteristics of the amorphous environment.
J Nanopart Res (2010) 12:993–1002 Table 3 Compositions evaluated by WAXS and EDS of EuxZr(1–x)O(2–x/2) solid solution and optical properties of CARBXX series
Sample
CARB00 A12 is the asymmetric ratio of the Eu3? emission (see main text) and sobs 1 and sobs 2 are the lifetimes of the Eu3? and of the host, respectively
997
x (WAXS)
–
x (EDS)
–
sobs 1 (ls) kexc = 394 nm
sobs 2 (ns) kexc = 373 nm
kem = 612 nm
kem = 430 nm
–
4.1
CARB10
10±1
11±2
4.4
469
3.2
CARB15
15±1
16±2
4.3
649
3.2
CARB20
22±1
18±2
4.6
406
3.7
4.1
489
3.3
CARB100
–
A21
is not possible and the effective lifetime sobs was evaluated using the following definition: R1 t IðtÞdt sobs ¼ R0 1 0 IðtÞdt
Fig. 2 SEM images of samples: (a) CARB100 (Eu-carbonate) and (b) CARB20 (Eu–Zr-carbonate)
The consistent PLE spectra visible in Fig. 3b show broadened and intense absorption bands in the range 360–465 nm that can be ascribed to the well known transition of Eu3? ions. The room temperature MCSPC decay curves of the PL emission are likewise reported in Fig. 3c, showing a slight non-exponential behaviour. For this reason, single exponential fitting
The non-exponential behaviour of the luminescence decay is attributed to the different environments surrounding the Eu3? ions, which is typical of the presence of inhomogeneities within the material. Moreover, the presence of traps which can act as nonradiative defects and quenching centres can, on the one hand, strongly reduce the emission lifetime with respect to the theoretical radiative emission and, on the other hand, produce non-exponential luminescence decay curves. Hydroxide groups and additional defects are the typical traps for the samples (Inokuti and Hirayama 1965; Yokota and Tanimoto 1967). Owing to the high concentration of active ions, energy may also migrate between Eu3? ions, as described by Fo¨rster (1948). The efficiency of such migration is related to the concentration of lanthanide ions and plays an important role in lattices with lowtrap concentrations. Energy migration allows an excited state to move in the lattice, and subsequently reach and interact with a trap (Inokuti and Hirayama 1965), thus boosting the effect of quenching of the luminescence which is otherwise known as ‘‘concentration quenching’’. Since in our samples the sobs values of the Eu3? emission (Table 3) appeared to be unrelated to the europium content, energy migration process could be not effective. Conversely, the high OH concentration may explain the short observed lifetimes of about 400–600 ls. Inspection of the k = 375–550 nm range revealed an highly interesting property within the sample series. In Fig. 4, the emission spectrum of doped
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emitted radiation. The lifetimes of the different hosts PL, measured at k = 430 nm, are reported in Table 3 (last column). The lifetimes of the Eu3? containing samples are independent of the lanthanide concentration and this excludes the energy transfer process between the host and the optically active Eu3? ions. Silica-supported Eu3?-doped zirconium carbonate nanoparticles
Fig. 3 Room temperature luminescence spectra and decay curves of CARBXX series: a PL (kexc = 394 nm), b PLE (kem = 612 nm), c MCSPC (kexc = 373 nm, kem = 612 nm). (7F0 is assumed as the ground state for all the transitions reported in the PLE spectrum)
samples CARB00, CARB 100 and CARB15 are reported together with the emission spectrum of calcinated CARB00 (700 °C for 12 h). An intense emission band with the maximum at 430 nm can be observed especially in the samples containing zirconium carbonate (CARB00 and CARB15), meanwhile it is completely absent in the calcinated CARB00 sample (amorphous ZrO2). CARB15 and CARB100 show also the absorption lines characteristic of europium(III) ions which can absorb part of the
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TEM micrographs of the sample CCORE showed the presence of spherical silica particles with an average size of approximately 30 nm (Fig. 5a). The silica supported Eu3?-doped zirconium carbonate nanoparticles, samples CG07, CG13 and CG20, were shown to comprise two amorphous phases as determined by XRD analysis, namely silica and Eu-doped zirconium carbonates. The WAXS pattern of CG7 sample shown in Fig. 6 is a representative example of the structural features noted in all of the systems. The weight ratio between the two amorphous components was evaluated by applying the least squares method developed by Riello et al. (2008) to the total XRD pattern of each sample. In order to perform such analyses, the patterns of the pure silica spheres and those of the Eu-doped zirconium carbonate powders comprising the compositions reported in Table 2 were also acquired. The two amorphous components and the global fit are displayed in Fig. 6, while the results are reported in Table 4. The XRD pattern for the calcinated sample CG07C with the relative fitting is shown in Fig. 7. The broad diffraction haloes indicate that following thermal treatment an highly amorphous Eu-doped zirconium oxide phase remains present. This structure is characteristic of all the calcinated samples for all the composition. However, Rietveld analysis (with the addition of alumina as an internal standard) allowed for quantification of the single phases and determination of the europium content in the doped zirconium oxide phase. The Rietveld analysis of these samples was carried out using the method proposed by Lutterotti et al. (1988) for the analysis of amorphous materials. Accordingly, the pattern of the amorphous zirconium–europium oxide phase was obtained by using the XRD pattern of cubic zirconia with very broad peaks. Consequently, we were able to evaluate the cell size of the cubic zirconia and the Eu content of the solid solution.
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Fig. 4 Room temperature PL spectra (kexc = 330 nm) of the samples carbonates CARB00, CARB 100 and CARB15. The PL spectra of the calcinated CARB00 (700 °C for 12 h) constituted of amorphous zirconium oxide is also reported. The self absorption of the broad PL emission of the carbonate matrix due to the presence of the Eu3? ions is evident in the spectra of CARB15 and CARB100 samples. The involved intra configurational 4f transitions are indicated by vertical arrows
999
The results of the quantitative phase analyses are reported in Table 4. As expected the weight fraction of the oxides obtained by the thermal treatment at 700 °C are less than the weight fractions of the parent carbonates. Moreover, the composition of the solid solutions obtained by using the cells refined with the method proposed by Lutterotti are very close to the expected nominal values. The morphology of the silica-supported carbonate samples can be appreciated from the TEM images shown in Fig. 5b, c. Evidently, the size of the carbonate particles is much smaller than the aggregates shown in Fig. 2. The growth of carbonate nanoparticles with an approximate 2 nm size occurred on the surface of the silica which constitutes the core (Fig. 5b, c). The observed aggregation of the silica particles is possibly related to the preparation method for TEM samples which involves evaporation of the liquid phase from a suspension of particles. The PL, PLE and MCSPC spectra for CGXX series and CGXXC series samples are shown in
Fig. 5 TEM micrographs: a supporting spherical silica particles (sample CCORE); b, c morphology of the silica-supported carbonate systems (sample CG13)
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Fig. 6 Typical XRPD pattern of silica-supported carbonate systems (sample CG07). The patterns of the two amorphous components (silica and carbonate phases) and the fit of the sample CG07, used to quantify the constituting amorphous phases, are shown
Figs. 8 and 9, respectively. The 5D0–7F2 and the 5 D0–7F4 transitions in the PL spectra did not exhibit strong splittings among the microstates. The peaks are very similar to the ones seen for the carbonate powders (Fig. 3). This similarity was also observed for the PLE spectra. Furthermore, the PLE spectra of the CGXX series (Fig. 8) shows the presence of broad bands below 400 nm which are absent in the CGXXC series (Fig. 9). The absence of such excitation bands in the calcinated CGXXC series suggests that this feature is related to the chemical nature of the sample (oxides versus carbonates), while the increased magnitude of the effect between the bulk CARBXX and the nanostructured CGXX series supports a size-dependent property of europiumdoped zirconium carbonates. The values of the effective emission decay time sobs for CGXX series samples are reported in Table 5, which includes the asymmetry factors A21. A comparison with Table 3, where sobs values were not correlated to the composition of the carbonate, shows that for CGXX series samples there is a general trend
Fig. 7 Typical XRPD pattern of the calcinated (700 °C for 12 h) silica-supported carbonate samples (sample CG07C). The broad peaks indicate that the sample is constituted of an highly amorphous Eu-doped zirconium oxide. A method based on the Rietveld analysis is used to quantify the Eu-doped zirconium oxide fraction with respect to the supporting silica (see main text). The sharp peaks belong to a-Al2O3 used as an internal standard (IS)
towards shorter sobs lifetimes with the increase of europium doping, which could indicate a concentration quenching effect. This effect could be due to differences in the preparation methods and the formation of nanostructures that strongly affect the final optical properties. A stronger dependency of sobs from the europium content is observed for the calcinated samples in the CGXXC series (Table 5). The calcination process removes the hydroxide species, thus transforming the carbonates into oxides and effectively removing most of the traps from the system. Hence, the occurrence of concentration quenching in the sample is more relevant, and one which strongly affects the luminescence lifetime.
Conclusion The structural and luminescence properties of europium(III)-doped zirconium carbonates, with differing
Table 4 Observed sample compositions for the CGXX and CGXXC series As prepared sample compositions (%wt)
Calcinated sample compositions (%wt)
Sample
Sample
CG07
Measured (least square method) Carbonate
SiO2
65 ± 2
35 ± 2
CG07C
Measured (Rietveld method) EuxZr(1–x)O(2–x/2)
SiO2
58 ± 1
42 ± 1
x 6±1
CG13
54 ± 2
46 ± 2
CG13C
49 ± 1
51 ± 1
13 ± 1
CG20
47 ± 2
53 ± 2
CG20C
45 ± 1
55 ± 1
22 ± 1
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Fig. 8 Room temperature luminescence spectra and decay curves of CGXX series: a PL (kexc = 394 nm), b PLE (kem = 612 nm), c MCSPC (kexc = 373 nm, kem = 612 nm). (7F0 is assumed as the ground state for all the transitions reported in the PLE spectrum)
europium contents, were examined both as bulk powders and silica-supported particles of 30 nm in size. The XRD patterns of the zirconium carbonates showed broad diffraction peaks resulting from the formation of different species with the formula Zr(OH)4–2x(CO3)x nZrO2 during their preparation. The morphology of the bulk powders was characterized by particles of micrometric size and irregular shape. In order to determine the Eu:Zr ratio, amorphous carbonate powders were calcinated at 1,000 °C for 1 h to obtain the relative crystalline oxide. The europium contents were calculated from a calibration line in which the cell volume, obtained by XRD measurements, was plotted against the amount of Eu
1001
Fig. 9 Room temperature luminescence spectra and decay curves of CGXXC series: a PL (kexc = 394 nm), b PLE (kem = 612 nm), c MCSPC (kexc = 373 nm, kem = 612 nm). (7F0 is assumed as the ground state for all the transitions reported in the PLE spectrum)
Table 5 Asymmetry factor and Lifetimes (kexc = 394 nm, kem = 612 nm) of the as prepared CGXX and calcinated CGXXC series sobs (ls)
Sample
A21
CG07
3.4
670
CG13
4.2
541
CG20
4.4
450
CG07C
4.4
1819
CG13C
4.7
1495
CG20C
4.5
1078
in the crystalline phase. Optical measurements on the prepared nanomaterials evidenced unique luminescence properties, influenced by the preparation
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method and the resulting morphology. Silica-supported Eu3?-doped zirconium carbonate nanoparticles were studied before and after a calcination treatment at 700 °C for 12 h. TEM micrographs evidenced the growth of carbonate nanoparticles of about 2 nm on the surface of the silica core. Rietveld analysis was used to quantify the constituting phases and to determinate the europium content in the doped zirconium oxide phase for the calcinated sample. For carbonate samples prepared as bulk materials, MCSPC measurements did not highlight a dependence between sobs and the concentration of europium ions, a likely consequence of the limited uniformity of the stoichiometry of the samples. Alternatively, for the nanostructured samples prior to calcination, a slight trend towards shorter sobs at higher Eu3? ions content was observed. Overall, we observed that the different preparation methods play an important role not only in determining the morphology of the nanostructure but also the luminescent properties of the samples. Acknowledgements The authors would like to thank Loris Bertoldo and Tiziano Finotto for conducting the WAXS analyses.
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