Synthesis of Metallic and Metal Oxide Nanoparticles Using Homopolymers as Solid Templates: Luminescent Properties of the Eu +3 Nanoparticle Products

: Starting from poly(4-vinylpyridine) ((P4VP) n ), poly(2-vinylpyridine) ((P2VP) n ), and [N= P(O 2 CH 2 CF 3 )] m - b -P2VP 20 block copolymers, a series of metal-containing homopolymers, (P4VP) n ⊕ MX m , (P2VP) n ⊕ MX m , and [N=P(O 2 CH 2 CF 3 )] m - b -P2VP 20 ] ⊕ MX m MX m = PtCl 2 , ZnCl 2 , and Eu(NO 3 ) 3 , have been successfully prepared by using a direct and simple solution methodology. Solid-state pyrolysis of the prepared metal-containing polymeric precursors led to the formation of a variety of different metallic and metal oxide nanoparticles (Pt, ZnO, Eu 2 O 3 , and EuPO 4 ) depending on the composition and nature of the polymeric template precursor. Thus, whereas Eu 2 O 3 nanostructures were obtained from europium-containing homopolymers ((P4VP) n ⊕ MX m and (P2VP) n ⊕ MX m ), EuPO 4 nanostructures were achieved using phosphorus-containing block copolymer precursors, [N=P(O 2 CH 2 CF 3 )] m - b -P2VP 20 ] ⊕ MX m with MX m = Eu(NO 3 ) 3 . Importantly, and although both Eu 2 O 3 and EuPO 4 nanostructures exhibited a strong luminescence emission, these were strongly influenced by the nature and composition of the macromolecular metal-containing polymer template. Thus, for P2VP europium-containing homopolymers ((P4VP) n ⊕ MX m and (P2VP) n ⊕ MX m ), the highest emission intensity corresponded to the lowest-molecular-weight homopolymer template, [P4VP(Eu(NO 3 ) 3 ] 6000 , whereas the opposite behavior was observed when block copolymer precursors, [N=P(O 2 CH 2 CF 3 )] m - b -P2VP 20 ] ⊕ MX m MX m = Eu(NO 3 ) 3 , were used (highest emission intensity corresponded to [N=P(O 2 CH 2 CF 3 )] 100 - b -[P2VP(Eu(NO 3 ) 3 ) x ] 20 ). The intensity ratio of the emission transitions: 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 , suggested a different symmetry around the Eu 3+ ions depending on the nature of the polymeric precursor, which also influenced the sizes of the prepared Pt ◦ , ZnO, Eu 2 O 3 , and EuPO 4 nanostructures.


Introduction
Polyphosphazenes, with the general formula [N=P(R 2 )] n (Figure 1), are an important class of inorganic polymers with relevant applications in material science [1].Since their first synthesis as high-molecular-weight and well-defined polymers in 1965 by Allcock and Kugel [2], the chemistry of these materials has experienced extraordinary growth due to the excellent properties (e.g., biodegradability [3,4], high fire resistance [5], and elasticity [6]) and the variety of potential and real applications [7] of those inorganic macromolecules, among other things.Currently, polyphosphazenes with a wide variety of ity [6]) and the variety of potential and real applications [7] of those inorganic macromolecules, among other things.Currently, polyphosphazenes with a wide variety of different chain architectures are known (see Figure 1) due to the extraordinary synthetic versatility ([N=PCl2]n) of the starting material, which allows a direct substitution of the chlorine atoms using an appropriate nucleophile [8][9][10][11][12].Moreover, in 1995, the groups of Allcock and Manners developed the living cationic chain-growth condensation polymerization of Cl3P=N-SiMe3 promoted by PCl5 [13].This polymerization provides a molecular weight control of poly(dichloro)phosphazene by simply altering the Cl3P=N-SiMe3/PCl5 ratio.It is well known that this living polymerization provides access to polyphosphazene block copolymers (see Figure 1) via a sequential monomer addition [14].Recently, polyphosphazenes have been exploited in nanoscience to stabilize metallic nanoparticles (Au and Ag, among others) and as a solid-state template for the synthesis of a wide variety of metallic and metal oxide nanoparticles [15].The great stabilization ability of polyphosphazene materials is mainly due to (i) the presence of coordinative moieties at the side groups of the main chain (i.e., R1-R4 side groups in Figure 1) and (ii) the presence of N atom in the main chain.Although it is not a very good ligand, this provides an additional coordinative site that can eventually prevent the agglomeration of the nanoparticles.In this regard, polyphosphazenes can easily form a macromolecular metal complex type, such as MXn•Polyphosphazene, which, after thermal treatment in the presence of oxidizing atmosphere (air), leads to the corresponding metal phosphate nanoparticles (MxPxOy) .On the other hand, using organic polymers based on poly(4-vinylpyridine) (P4VP) chains, such as PSP-co-P4VP (PS = polystyrene), or chitosan, the pure metal oxide MxOy nanoparticles were successfully achieved [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59].Thus, aiming to evaluate the combined effect of both polyphosphazenes and poly(vinylpiridine) materials in the formation of metallic nanoparticles, in this report, we describe the synthesis of metallic phosphate nanoparticles of europium using polyphosphazene-b-poly(2-vinylpiridine) (PP-b-P2VP) block copolymers as a solid-state template.Also, as model reactions, we describe the formation of pure Pt nanoparticles and metal oxide nanoparticles (ZnO and Eu2O3) by using P2VP and P4VP homopolymers as solid-state templates.
Considering the results of obtaining nanoparticles using macromolecular complexes as precursors with polyphosphazenes as polymers  and, furthermore, obtaining nanoparticles using chitosan and PSP-co-P4VP polymers [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59], we observed a possible dependence of the composition of the nanoparticles on the nature of the polymer, acting as a mold in the solid state.If, instead, the polymer matrix of the precursor is made up of polyphosphazenes, the formation of nanoparticles of metal phosphates and pyrophosphates is usual [20,[24][25][26]28,29,31,35,36,42], while when the macromolecular precursor is an organic polymer that does not contain phosphorus in its chain, nanoparticles of pure metal oxides are normally obtained [47][48][49]51,[53][54][55]57].Therefore, the main objective of this work was to use a polymer that contains a phosphazenic unit, such as Recently, polyphosphazenes have been exploited in nanoscience to stabilize metallic nanoparticles (Au and Ag, among others) and as a solid-state template for the synthesis of a wide variety of metallic and metal oxide nanoparticles [15].The great stabilization ability of polyphosphazene materials is mainly due to (i) the presence of coordinative moieties at the side groups of the main chain (i.e., R 1 -R 4 side groups in Figure 1) and (ii) the presence of N atom in the main chain.Although it is not a very good ligand, this provides an additional coordinative site that can eventually prevent the agglomeration of the nanoparticles.In this regard, polyphosphazenes can easily form a macromolecular metal complex type, such as MX n •Polyphosphazene, which, after thermal treatment in the presence of oxidizing atmosphere (air), leads to the corresponding metal phosphate nanoparticles (M x P x O y ) .On the other hand, using organic polymers based on poly(4-vinylpyridine) (P4VP) chains, such as PSP-co-P4VP (PS = polystyrene), or chitosan, the pure metal oxide M x O y nanoparticles were successfully achieved [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59].Thus, aiming to evaluate the combined effect of both polyphosphazenes and poly(vinylpiridine) materials in the formation of metallic nanoparticles, in this report, we describe the synthesis of metallic phosphate nanoparticles of europium using polyphosphazene-b-poly(2-vinylpiridine) (PP-b-P2VP) block copolymers as a solid-state template.Also, as model reactions, we describe the formation of pure Pt nanoparticles and metal oxide nanoparticles (ZnO and Eu 2 O 3 ) by using P2VP and P4VP homopolymers as solid-state templates.
Considering the results of obtaining nanoparticles using macromolecular complexes as precursors with polyphosphazenes as polymers  and, furthermore, obtaining nanoparticles using chitosan and PSP-co-P4VP polymers [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59], we observed a possible dependence of the composition of the nanoparticles on the nature of the polymer, acting as a mold in the solid state.If, instead, the polymer matrix of the precursor is made up of polyphosphazenes, the formation of nanoparticles of metal phosphates and pyrophosphates is usual [20,[24][25][26]28,29,31,35,36,42], while when the macromolecular precursor is an organic polymer that does not contain phosphorus in its chain, nanoparticles of pure metal oxides are normally obtained [47][48][49]51,[53][54][55]57].Therefore, the main objective of this work was to use a polymer that contains a phosphazenic unit, such as [N=P(O 2 CH 2 CF 3 )], and an organic unit, such as P2VP, in its chain, to check whether the nanoparticles obtained using this copolymer as a precursor would produce nanoparticles of metal phosphates, only pure metal oxides, or a mixture of phosphates and metal oxides.These results could advance the knowledge of the formation mechanism in the solid state, using macromolecular complexes as precursors and polymers as templates.

Synthesis of Macromolecular Metal Complex of Type MX n -Polymer
In a typical procedure, an equimolar amount of the corresponding polymer and the desired metallic precursor was placed in a Schlenk tube and 20 mL of dichloromethane was added.The heterogeneous mixture was stirred at room temperature for 8 days.The solid obtained was filtered and washed with dichloromethane.The obtained solid residue was dried under vacuum for 3 h.For further experimental details, see Table S1 in the Electronic Supplementary Materials.Next, the obtained solids were placed into a box furnace (lab tech) and treated under a pyrolysis program.The oven remained at 200 • C for 10 min, then its temperature was raised to 800 • C in 50 min, to finally remain at this temperature for 4 h, in the air atmosphere.The pyrolytic residues were characterized by (i) X-ray diffraction (XRD; Siemens D-5000 diffractometer with θ-2θ geometry), whereby XRD data were collected using Cu-Kα radiation (40 kV, 30 mA), (ii) elemental microanalysis (performed via energy-dispersive X-ray analysis using a NORAN Instrument micro-probe attached to the scanning electron microscope), (iii) SEM analysis (images were acquired with a Philips EM 300 scanning electron microscope), (iv) energy-dispersive X-ray analysis (EDAX; NORAN Instrument micro-probe attached to a JEOL 5410 scanning electron microscope), and (v) high-resolution transmission electron microscopy (HR-TEM; JEOL 2000FX TEM microscope at 200 kV, Tokyo, Japan) to characterize the average particle size, distribution, and elemental and crystal composition.The average particle size was calculated using the Digital Micrograph software (Windows 2000 Professional).
Comparative TG/DTA analyses of Zn-based macromolecular complexes of (1a) and (1a-Zn) and the corresponding non-coordinated (1a) chains clearly showed two main decomposition steps, one corresponding to non-coordinated pyridine groups (390-410 • C) [55] and the other, at 430-650 • C, corresponding to (1a-Zn) moieties (Figure 2).Similar behavior was observed in all other synthesized macromolecular complexes.The metallic coordination degrees of the polymeric materials were calculated on the basis of the amount (%) of final residue, ZnO, obtained in each TG/DTA analysis [54,55].Thus, coordination degrees ranging from >99% to 47% were observed depending on the employed polymeric material and metallic source (analyses can be performed for other macromolecular complexes).
Comparative TG/DTA analyses of Zn-based macromolecular complexes of (1a) and (1a-Zn) and the corresponding non-coordinated (1a) chains clearly showed two main decomposition steps, one corresponding to non-coordinated pyridine groups (390-410 °C) [55] and the other, at 430-650 °C, corresponding to (1a-Zn) moieties (Figure 2).Similar behavior was observed in all other synthesized macromolecular complexes.The metallic coordination degrees of the polymeric materials were calculated on the basis of the amount (%) of final residue, ZnO, obtained in each TG/DTA analysis [54,55].Thus, coordination degrees ranging from >99% to 47% were observed depending on the employed polymeric material and metallic source (analyses can be performed for other macromolecular complexes).
Thus, by comparing the residue assigned to the ZnO, considering a 100% coordination with the obtained residue, a coordination degree could be estimated [22,23].Values were in the range of 47-100% (see the Supplementary Materials).
The structures of the synthesized materials were also investigated by SEM and EDS.Thus, SEM images of PtCl 2 -based materials ((1a-Pt), (1b-Pt), and (1c-Pt), Figure 6) after pyrolysis showed the presence of dense aggregated grains.The high aggregation created the typical metal-foam-type morphology [32].EDS analysis supported the presence of Pt • as the sole element (Figure 6d).
SEM images of the as-synthesized ZnO materials showed (Figure 7) the presence of a cuboidal-like nanostructure.These nanostructures were densely packed, exhibiting similar structures as those observed in previous works of the group [48].Again, EDS analysis supported the presence of pure phases of ZnO.

EDS Analysis of (1c-Zn)
The SEM images of the as-prepared Eu 2 O 3 material (Figure 8) showed cotton-like morphologies, with the EDS analysis being in accordance with the presence of Eu 2 O 3 .

EDS Analysis of (1c-Eu)
As-prepared nanostructured materials were also investigated using TEM.Thus, TEM analysis of nanostructured Pt prepared by pyrolysis of the macromolecular precursors (a) (1a-Pt), (c) (1b-Pt), and (d) (1c-Pt) showed the presence of platinum nanoparticles with relatively monodisperse sizes (62 nm, 47 nm, and 95 nm, respectively, see Figure 9).According to the electron diffraction images, the Pt sample from the (1c-Pt) precursor appeared to be more crystalline than that from the 1a-Pt precursor.The structures of the synthesized materials were also investigated by SEM and Thus, SEM images of PtCl2-based materials ((1a-Pt), (1b-Pt), and (1c-Pt), Figure 6) pyrolysis showed the presence of dense aggregated grains.The high aggregation cre the typical metal-foam-type morphology [32].EDS analysis supported the presence o as the sole element (Figure 6d).SEM images of the as-synthesized ZnO materials showed (Figure 7) the presen a cuboidal-like nanostructure.These nanostructures were densely packed, exhibiting ilar structures as those observed in previous works of the group [48].Again, EDS ana supported the presence of pure phases of ZnO.

EDS Analysis of (1c-Zn)
The SEM images of the as-prepared Eu2O3 material (Figure 8) showed cotton-like morphologies, with the EDS analysis being in accordance with the presence of Eu2O3.

EDS Analysis of (1c-Zn)
The SEM images of the as-prepared Eu2O3 material (Figure 8) showed cotto morphologies, with the EDS analysis being in accordance with the presence of Eu2O As-prepared nanostructured materials were also investigated using TEM.Thus, TEM analysis of nanostructured Pt prepared by pyrolysis of the macromolecular precursors (a) (1a-Pt), (c) (1b-Pt), and (d) (1c-Pt) showed the presence of platinum nanoparticles with relatively monodisperse sizes (62 nm, 47 nm, and 95 nm, respectively, see Figure 9).According to the electron diffraction images, the Pt sample from the (1c-Pt) precursor appeared to be more crystalline than that from the 1a-Pt precursor.TEM images of nanostructured ZnO prepared by pyrolysis of the macromolecular precursors (a) (1a-Zn), (b) (1b-Zn), and (c) (1c-Zn) showed the presence of rather monodisperse nanoparticles, with average sizes of 70 nm, 60 nm, and 80 nm (see Figure 10).According to the electron diffraction images, the ZnO sample from the (1a) precursor appeared to be more crystalline than that from the (1b) and (1c) precursors.TEM images of nanostructured ZnO prepared by pyrolysis of the macromolecular precursors (a) (1a-Zn), (b) (1b-Zn), and (c) (1c-Zn) showed the presence of rather monodisperse nanoparticles, with average sizes of 70 nm, 60 nm, and 80 nm (see Figure 10).According to the electron diffraction images, the ZnO sample from the (1a) precursor appeared to be more crystalline than that from the (1b) and (1c) precursors.
TEM images of nanostructured Eu 2 O 3 obtained by pyrolysis of the macromolecular precursors (a) (1a-Eu), (b) (1b-Eu), and (c) (1c-Eu) showed the presence of concatenated nanostructures with particle sizes ranging from 50 to 60 nm (see Figure 11).As a general trend, we observed smaller particle sizes when high-molecular-weight precursors were employed, which agrees with the higher surfactant ability of these solid templates during grain growing.According to the electron diffraction images, the Eu 2 O 3 samples from all the precursors appeared to be of similar crystallinity.

EuPO4
The pyrolysis of the polyphosphazene block copolymer metal complexes, (2a-Eu), (2b-Eu), and (2c-Eu), using the previously described experimental conditions, led to the formation of nanostructured EuPO4.The synthesis of pure phases of monoclinic EuPO4 (diffraction planes (110), ( 101), ( 200), ( 002), ( 120), (−221), (−311), and (−041)) [60] was confirmed by X-ray diffraction analysis (Figure 12).SEM images of the as-obtained EuPO 4 showed a typical foam-like morphology for all the examined nanostructured materials (Figure 13) [61,62].Importantly, EDS analysis exhibited the presence of Eu, P, and O, which agreed with the formation of pure EuPO 4 phases (Figure 13).SEM images of the as-obtained EuPO4 showed a typical foam-like morphology for all the examined nanostructured materials (Figure 13) [61,62].Importantly, EDS analysis exhibited the presence of Eu, P, and O, which agreed with the formation of pure EuPO4 phases (Figure 13).As-prepared EuPO4 nanostructures were also examined by TEM.Thus, TEM images (Figure 14) showed well-defined nanoparticles with average sizes ranging from 25 to 40 nm.Importantly, interplanar distances of 0.499 nm and 0.503 nm, corresponding to the plane (−101) of monoclinic EuPO4, were clearly observed for samples resulting from the pyrolysis of (2a-Eu) and (2b-Eu) precursors.The electron diffraction patterns of the EuPO4 nanostructures prepared here demonstrated their crystalline nature.As-prepared EuPO 4 nanostructures were also examined by TEM.Thus, TEM images (Figure 14) showed well-defined nanoparticles with average sizes ranging from 25 to 40 nm.Importantly, interplanar distances of 0.499 nm and 0.503 nm, corresponding to the plane (−101) of monoclinic EuPO 4 , were clearly observed for samples resulting from the pyrolysis of (2a-Eu) and (2b-Eu) precursors.The electron diffraction patterns of the EuPO 4 nanostructures prepared here demonstrated their crystalline nature.A possible formation mechanism of the nanoparticles can be proposed on the basis of previous studies on solid-state formation of nanostructured metal oxide materials using the same synthetic approach [38,45,58] (see the Supplementary Materials).According to these studies, the first step of heating the samples involves the formation of a 3D network to produce a thermally stable matrix.This step is crucial because it offsets the sublimation.The first heating step could involve a crosslinking of the polyphosphazene-b-poly(2-vinylpiridine), poly(4-vinylpyridine), or poly(2-vinylpyridine) polymers, yielding a 3D matrix containing the PtCl2, ZnCl2, and Eu(NO3)3 metals joined to the polymeric chain.The next stage could be the beginning of the organic carbonization, producing holes where the nanoparticles begin to nucleate.As it was confirmed in earlier studies [29], the formation of Pt, ZnO, Eu2O3, and EuPO4 nanoparticles could occur over a layered graphitic carbon host, which is lost near the final annealing temperature, i.e., 800 °C.

Optical Properties
The bandgap values, Eg, of as-prepared ZnO ranged from 3.23 to 4.24 eV depending on the macromolecular precursor used during the pyrolysis treatment (see the Tauc plots and table of tabulated values in the Supplementary Materials).As a result of the smaller nanoparticle sizes obtained by using these macromolecular precursors as solid-state templates, in comparison with those of other published solid templates [48], the obtained bandgap values were slightly higher than those expected for nanostructured ZnO materials [62].On the other hand, the bandgap values of as-prepared Eu2O3 oxides were in the range of 4.34 and 4.52 eV, which is consistent with those reported in the literature for these materials, suggesting an insulator behavior [63].A possible formation mechanism of the nanoparticles can be proposed on the basis of previous studies on solid-state formation of nanostructured metal oxide materials using the same synthetic approach [38,45,58] (see the Supplementary Materials).According to these studies, the first step of heating the samples involves the formation of a 3D network to produce a thermally stable matrix.This step is crucial because it offsets the sublimation.The first heating step could involve a crosslinking of the polyphosphazene-bpoly(2-vinylpiridine), poly(4-vinylpyridine), or poly(2-vinylpyridine) polymers, yielding a 3D matrix containing the PtCl 2 , ZnCl 2 , and Eu(NO 3 ) 3 metals joined to the polymeric chain.The next stage could be the beginning of the organic carbonization, producing holes where the nanoparticles begin to nucleate.As it was confirmed in earlier studies [29], the formation of Pt, ZnO, Eu 2 O 3 , and EuPO 4 nanoparticles could occur over a layered graphitic carbon host, which is lost near the final annealing temperature, i.e., 800 • C.

Optical Properties
The bandgap values, E g , of as-prepared ZnO ranged from 3.23 to 4.24 eV depending on the macromolecular precursor used during the pyrolysis treatment (see the Tauc plots and table of tabulated values in the Supplementary Materials).As a result of the smaller nanoparticle sizes obtained by using these macromolecular precursors as solid-state templates, in comparison with those of other published solid templates [48], the obtained bandgap values were slightly higher than those expected for nanostructured ZnO materials [62].On the other hand, the bandgap values of as-prepared Eu 2 O 3 oxides were in the range of 4.34 and 4.52 eV, which is consistent with those reported in the literature for these materials, suggesting an insulator behavior [63].As expected, the as-prepared nanostructured Eu 2 O 3 and EuPO 4 exhibited luminescence properties due to the presence of the Eu 3+ ions [64][65][66][67][68]. Thus, the emission spectra (λ exc = 395 nm) of Eu 2 O 3 synthesized from precursors (1a-Eu), (1b-Eu), and (1c-Eu) (Figure 15) showed the characteristic pattern of the lanthanide oxide series.It is important to note that the intensity of the emission is affected by the symmetry of the Eu 3+ environment.Thus, the 5 D 0 → 7 F 1 lines originated from the magnetic dipole transition, while the 5 D 0 → 7 F 2 lines originated from the electric dipole transitions [66].The electric dipole transition is permitted only when Eu 3+ ions occupy sites with no inversion center, and it is sensitive to local symmetry.This fact induces the relatively strong 5 D 0 → 7 F 2 transition.Interestingly, the photoluminescence intensity of the electric-dipole transition of 5 D 0 → 7 F 2 was stronger than the magnetic dipole transition of 5 D 0 → 7 F 1 when P4VP macromolecular metallic precursors were employed as a solid template (note the opposite behavior when P2VP precursors were used, see Figure 15).It is well known that the 5 D 0 → 7 F 2 transition is more sensitive to symmetry than the 5 D 0 → 7 F 1 transition.The symmetry around the Eu 3+ ions in as-synthesized Eu 2 O 3 was higher in materials prepared from the pyrolysis of P2VP-based metallic precursors than that of the materials prepared by pyrolysis of P4VP-based templates.These results clearly pointed out the importance of the chosen solid template over the symmetry of the as-obtained Eu 2 O 3 nanomaterials.As expected, the as-prepared nanostructured Eu2O3 and EuPO4 exhibited luminescence properties due to the presence of the Eu 3+ ions [64,[65][66][67][68]. Thus, the emission spectra (λexc = 395 nm) of Eu2O3 synthesized from precursors (1a-Eu), (1b-Eu), and (1c-Eu) (Figure 15) showed the characteristic pattern of the lanthanide oxide series.It is important to note that the intensity of the emission is affected by the symmetry of the Eu 3+ environment.Thus, the 5 D0→ 7 F1 lines originated from the magnetic dipole transition, while the 5 D0→ 7 F2 lines originated from the electric dipole transitions [66].The electric dipole transition is permitted only when Eu 3+ ions occupy sites with no inversion center, and it is sensitive to local symmetry.This fact induces the relatively strong 5 D0 → 7 F2 transition.Interestingly, the photoluminescence intensity of the electric-dipole transition of 5 D0 → 7 F2 was stronger than the magnetic dipole transition of 5 D0 → 7 F1 when P4VP macromolecular metallic precursors were employed as a solid template (note the opposite behavior when P2VP precursors were used, see Figure 15).It is well known that the 5 D0 → 7 F2 transition is more sensitive to symmetry than the 5 D0 → 7 F1 transition.The symmetry around the Eu 3+ ions in as-synthesized Eu2O3 was higher in materials prepared from the pyrolysis of P2VP-based metallic precursors than that of the materials prepared by pyrolysis of P4VP-based templates.These results clearly pointed out the importance of the chosen solid template over the symmetry of the as-obtained Eu2O3 nanomaterials.
Table 1 presents a summary of all the relevant data (particle sizes, morphology, and optical properties) of the nanostructured Pt, ZnO, Eu 2 O 3 , and Eu(NO 3 ) 3 prepared by using different macromolecular solid-state precursors.The analysis of the experimental data collected in Table 1 led to the conclusion that larger nanoparticles were created by using solid polymeric templates of lower-molecularweight distributions.On the other hand, it seems that the as-obtained morphologies of the nanostructured materials were not significantly influenced by the nature of the macromolecular solid template.

Conclusions
The solid-state pyrolysis of the metal-polymer precursors ((P4VP) n ⊕MX m and (P2VP) n ⊕MX m , M = PtCl 2 , ZnCl 2 , and Eu(NO 3 ) 3 ) led to Pt, ZnO, and Eu 2 O 3 nanostructures, respectively.On the other hand, EuPO 4 nanostructured material can be obtained by using polyphosphazene block copolymer metal complexes as a solid-state template during the pyrolysis treatment of (2a-Eu), (2b-Eu), and (2c-Eu).These results clearly pointed out that the presence of phosphorous atoms in the polyphosphazene block controlled the formation of nanostructured EuPO 4 materials during pyrolysis, even when the Eu(NO 3 ) 3 was selectively coordinated in the P2VP block.By comparing the nature, morphology, size, and properties of the nanostructured Pt, ZnO, Eu 2 O 3 , and EuPO 4 materials, it was clear that the length of the polymeric chains controlled the size of the obtained nanoparticles.Thus, a smaller particle size was obtained by using longer polymeric chains.Analysis of the luminescent properties of the Eu 3+ -containing nanostructured materials revealed that the symmetry of Eu 3+ ions was strongly affected by the nature of the polymeric solid precursors.The herein described results represent a step forward in understanding the experimental parameters controlling the formation of nanoparticles in solid state and constitute a new advance toward the elucidation of the mechanisms involved in the formation of these nanoparticles in the solid state.
[a] Determined by TEM.[b] Degree of coordination of the corresponding metal source with the respective polymer material.Calculated by TG/DTA.[c] [PP] = [N=P(OCH 2 CF 3 ) 2 ] n .

Table 1 .
Relevant experimental data of the as-prepared nanostructured Pt, ZnO, Eu 2 O 3 , and EuPO 4 materials.