Jeannette Dexpert-Ghys

Unusual fluorescent properties of Eu3+ in oxyapatites

Abstract The Eu3+ fluorescence in the continous solid solution Ca10-xEux(PO4)601+x/2□1-x/2, with 0.05⩽x⩽ , is studied at 300 and 77 K. The emission mainly arises from the 5D0 level. The dependence upon the composition shows that Eu3+ ions occupy preferentially the calcium site II of the apatite structure. Eu3+ ions occupy site I only for x>1. The emission lines are broadened as a result of anion vacancies. Site-selective laser excitation of Eu3+ in site II reveals the presence of two types of centers, whose structural model is proposed. The emission spectra present the following unusual features for Eu3+: (a) high value of the 5 D 0 level (⋍17500 cm -1 ); (b) large 7 F 1 splitting; and (c), the very strong intensity of the 5 D 0 → 7 F 0 emission line. The covalent character of the Eu3+-02- bond correlated to a strong crystal field of nearly C∞v symmetry allows as to propose the assignement of the 5 D 0 → 7 F 1,2 lines. Discussion of this exceptional behavior of Eu3+ is given in terms of J-mixing.

Site Selective Spectroscopy and Structural Analysis of Yttria-Doped Zirconias

Abstract Yttria-stabilized zirconias Zr 1− x Y x O 2−0.5 x (tetragonal, cubic fluorite, and cubic C Ln 2 O 3 -type forms) are investigated by spectroscopic methods. Optically active europium ions that partially substitute yttrium ions act as a structural microprobe. Both conventional ultraviolet and dye laser (site-selective) excitation are used. The yttria-stabilized zirconias may be well described by a cationic sublattice in which tetravalent and trivalent cations are statistically distributed. The anionic sublattice accommodates vacancies at random on oxygen positions. These vacancies in turn cause complex oxygen displacements giving rise to what may be described as a “glass of anions.”

Study of new lanthanide complexes of 2,6-pyridinedicarboxylate: synthesis, crystal structure of Ln(Hdipic)(dipic) with Ln=Eu, Gd, Tb, Dy, Ho, Er, Yb, luminescence properties of Eu(Hdipic)(dipic)

Abstract This paper presents the hydrothermal synthesis of a series of new isomorphous bis-dipicolinato lanthanide complexes: Ln(Hdipic)(dipic) with Ln=Eu, Gd, Tb, Dy, Ho, Er, Yb, and dipic=2,6-pyridinedicarboxylate. A structural study has been realised for the Ho3+ complex. It crystallises in a two-dimensional network, where sheets are parallel to the (100) plane. The luminescent properties of the analogous Eu3+ complex have been investigated. The composition of the 7FJ levels is consistent with a true C1 local symmetry: six oxygen and two nitrogen atoms forming a distorted square antiprism. The 5D0 emission lifetime is only slightly shorter than in [Eu(dipic)3]3− in solution, but the ligand to metal energy transfer is much less efficient.

Structural studies in lead germanate glasses: EXAFS and vibrational spectroscopy

The Raman, IR absorption and EXAFS spectra at the Ge K-edge and Pb LIII-edge of eight lead germanate glasses, with general formula xPbO(1−x)GeO2 with x = 0.20, 0.25, 0.33, 0.40, 0.50, 0.53, 0.56 and 0.60, have been measured. The occurrence of [GeO6] units besides [GeO4] could not be deduced unambiguously from the data. The vibrational and EXAFS data agree with a progressive depolymerization of the network. Starting from all Ge atoms linked to four bridging oxygens in GeO2 (x = 0), the number of tetrahedral units with one or two non-bridging oxygens increases with x. At low content, Pb2+ ions act as modifiers in the germanate structure, but to a lesser extent than an equivalent number of alkaline ions.

X-ray absorption study of the ZrO2Y2O3 system

A complete EXAFS analysis of the ZrO/sub 2/-Y/sub 2/O/sub 3/ system has been performed at both the yttrium and zirconium K absorption edges. The main result of this work is that the first average cation-oxygen distances are quite different and remain similar to those known for the pure oxides, namely, 2.16 A for ZrO/sub 2/ and 2.28 A for Y/sub 2/O/sub 3/. The EXAFS spectra show qualitatively that the yttrium network is much more sensitive to the Y/sup 3 +//Zr/sup 4 +/ substitution than the zirconium one.

Biomimetic nanocrystalline apatites: Emerging perspectives in cancer diagnosis and treatment

Nanocrystalline calcium phosphate apatites constitute the mineral part of hard tissues, and the synthesis of biomimetic analogs is now well-mastered at the lab-scale. Recent advances in the fine physico-chemical characterization of these phases enable one to envision original applications in the medical field along with a better understanding of the underlying chemistry and related pharmacological features. In this contribution, we specifically focused on applications of biomimetic apatites in the field of cancer diagnosis or treatment. We first report on the production and first biological evaluations (cytotoxicity, pro-inflammatory potential, internalization by ZR-75-1 breast cancer cells) of individualized luminescent nanoparticles based on Eu-doped apatites, eventually associated with folic acid, for medical imaging purposes. We then detail, in a first approach, the preparation of tridimensional constructs associating nanocrystalline apatite aqueous gels and drug-loaded pectin microspheres. Sustained releases of a fluorescein analog (erythrosin) used as model molecule were obtained over 7 days, in comparison with the ceramic or microsphere reference compounds. Such systems could constitute original bone-filling materials for in situ delivery of anticancer drugs.

New nanoplatform based on Gd2O2S:Eu3+ core: synthesis, characterization and use for in vitro bio-labelling

The synthesis of Gd2O2S:Eu3+ nanoparticles (NPs), from hydroxycarbonate precursor precipitation followed by sulfuration in a H2S/Ar atmosphere at 750 °C; is reported. It is the first time that the size of Gd2O2S:Eu3+ NPs can be finely tuned from 60 nm to more than 200 nm by controlling the precipitation medium, the maturation time and the sulfuration route. The oxysulfide Gd2O2S:Eu3+ NPs emit strong red luminescence at 624 nm when excited by near UV (363 nm) or by X-rays. They may thus be considered as nano-phosphors and nano-scintillators. Then, the surface of oxysulfide NPs has been modified by an amino-silica or by a mesoporous silica shell (thickness 10–15 nm). The luminescence intensity of europium in gadolinium oxysulfide NPs has been maintained in the amino-silica coated particles Gd2O2S:Eu3+@SiO2-APTMS, whereas it has been significantly enhanced in the mesoporous silica coated Gd2O2S:Eu3+@mSiO2. This versatile new nanoplatform can be easily internalized in living NIH3T3 mouse cells. It is not cytotoxic up to 1 mg mL−1 and can be easily imaged by epifluorescence microscopy with excitation in the NUV. Consequently this spherical monodispersed Gd2O2S:Eu3+ nanophosphor could be considered as a very promising new fluorescent probe for bio-labelling, better than the corresponding oxide or fluoride nanoparticles.

APTES-Modified RE2O3:Eu3+ Luminescent Beads: Structure and Properties

Europium-doped lanthanide oxide RE(2)O(3):Eu(3+) (RE = Y or Gd) luminescent beads, with a spherical shape and a diameter of 150 ± 15 nm, have been modified by reaction with 3-aminopropyltriethoxysilane (APTES), in order to introduce reactive amine groups at their surfaces. The direct silanation has resulted in the formation of a nanometric layer at the surface of the beads, with an optimum grafting rate of 0.055 ± 0.005 mol APTES/mol RE(2)O(3). Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies confirmed the condensation of an organosilane layer, made of cross-linked -O-Si-O-Si- and of groups -O-Si-R (with R = (CH(2))(3)NH(2) or O-Et). Titration of the accessible amine groups has been performed by simultaneously measuring the luminescence of grafted fluorescein isothiocyanate and that of core particles: there are about 2.3 × 10(4) (2.8 × 10(4)) -NH(2) per Y(2)O(3):Eu(3+) (Gd(2)O(3):Eu(3+)) bead. The isoelectronic point was shifted by one pH unit after APTES modification. The surface modification by APTES at least preserved (for Gd(2)O(3):Eu(3+)) or improved (for Y(2)O(3):Eu(3+)) the red emission of the beads.

Synthesis and luminescence properties of water dispersible Eu3+-doped boehmite nanoparticles

Nanocrystallized boehmite γ-AlOOHnH2O had been synthesized by spray-drying (SD) of a solution of aluminium tri-sec-butoxide peptized by nitric acid. The sub-micronic spherical particles obtained had an average diameter of 500 nm and were built of 100 nm or less platelet-like sub-particles. The average crystallite size calculated from XRD was 1.6 nm following the axis (i.e. one unit cell) and 3–4 nm perpendicular to . As a result of the nanometric sizes of crystallites, there was a large surface free for water adsorption and it was found to be n = 1.18 ± 0.24H2O per AlOOH. The SD spheres spontaneously dispersed in water at room temperature and formed stable—over months—suspensions with nanometre-size particles (25–85 nm). Luminescent europium-doped nanocrystallized boehmites AlOOH:Eu (Al0.98Eu0.02OOHnH2O) were synthesized the same way by SD and demonstrated the same crystallization properties and morphologies as the undoped powders. It is inferred from the Eu3+ luminescence spectroscopy that partly hydrated europium species are immobilized on the boehmite nanocrystals where they are directly bonded to α(OH) groups of the AlOOH surface. The europium coordination is schematically written [Eu3+(OH)α(H2O)7−α/2 ]. The europium-doped boehmite from SD spontaneously dispersed in water: the luminescence spectroscopy proves that most of the Eu3+ ions were detached from the NPs during water dispersion. The AlOOH:Eu nanoparticles were modified by the amine acid asparagine (ASN). The modification aimed to render the NPs compatible for further bio-functionalization. After surface modification, the NPs easily dispersed in water; the luminescence spectra after dispersion prove that the Eu3+ ions were held at the boehmite surface.

Organosilylated Complex [Eu(TTA)3(Bpy-Si)]: A Bifunctional Moiety for the Engeneering of Luminescent Silica-Based Nanoparticles for Bioimaging

A new highly luminescent europium complex with the formula [Eu(TTA)3(Bpy-Si)], where TTA stands for the thenoyltrifluoroacetone, (C4H3S)COCH2COCF3, chelating ligand and Bpy-Si, Bpy-CH2NH(CH2)3Si(OEt)3, is an organosilyldipyridine ligand displaying a triethoxysilyl group as a grafting function has been synthesized and fully characterized. This bifunctional complex has been grafted onto the surface of dense silica nanoparticles (NPs) and on mesoporous silica microparticles as well. The covalent bonding of [Eu(TTA)3(Bpy-Si)] inside uniform Stöber silica nanoparticles was also achieved. The general methodology proposed could be applied to any silica matrix, allowed high grafting ratios that overcome chelate release and the tendency to agglomerate. Luminescent silica-based nanoparticles SiO2-[Eu(TTA)3(Bpy-Si)], with a diameter of 28 ± 2 nm, were successfully tested as a luminescent labels for the imaging of Pseudomonas aeruginosa biofilms. They were also functionalized by a specific monoclonal antibody and subsequently employed for the selective imaging of Escherichia coli bacteria.