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International audience; Extensive research on nanosized ZnO has proven that its optical properties are challenging to control due to a number of possible defects producing various emissions in the visible range. Our group proposed a low-temperature, supercritical-fluid-driven synthesis of isotropic nanosized particles that exhibit a unique and unprecedentedly pure excitonic emission, comparable to that of single crystals. The present article reports the growth mechanism at the origin of the unexpectedly pure excitonic emission as well as a more detailed study of its optical properties at liquid helium temperatures. The ZnO phase is obtained via the thermal decomposition of an intermediate ZnO2 phase. No bulk defect luminescence is detected, and the synthesis route leaves a “ZnO2-like” surface able to neutralize the formation of surface defects, which can contribute to visible emissions. The luminescence measurements were performed at liquid helium temperature to enable the identification of excitons. The investigation of the photoluminescence properties confirms a strong excitonic emission in the UV region with no visible band and sheds light on a phonon coupling with the E2 high vibrational mode.

Recently, we discovered a huge photochromic effect for ZnO/MoO3 powder mixtures compared with the corresponding single oxides. The former study focused on the coloring efficiency after UV-light irradiation and demonstrated that the pre-existing electrons in the conductive band of ZnO are of huge importance to the photochromism efficiency. Herein, the creation of the “self-closed Schottky barrier” at the solid–solid interfaces between the two oxides, associated with the full redox reaction at the origin of the photochromic properties, was modulated by (i) doping ZnO with Al3+ ions, (ii) annealing the powder mixture under low p(O2) atmosphere, and (iii) synthesizing our own ZnO nanoparticles and MoO3 particles using a polyol process. The characterization of the colouring effect under irradiation as well as the self-bleaching process allowed shedding light on this very complex photochromic mechanism. The coloring and bleaching efficiency (i.e. possibility to darken to more or less deep blue and to come back to the virgin material optical properties without any deterioration) depends upon multiple interconnected parameters controlling either the particle size and the interface areas between MoO3 and ZnO oxides or the number of pre-electrons in conduction bands of ZnO and MoO3 oxides. By correctly interpreting the ins and outs of the photochromism taking place at the created Schottky barriers in these binary ZnO/MoO3 mixtures, the exchange of the electrons and the oxygen anions through this Schottky interface can be manipulated in order to optimize the huge photochromism phenomenon.

International audience; ZnO/MoO3 powder mixture exhibits a huge photochromic effect in comparison with the corresponding single oxides. The coloring efficiency of such combined material after UV-light irradiation was studied in terms of intensity, kinetics, and ZnO/MoO3 powder ratio. Additionally, the incidence of the pretreatment step of the ZnO and MoO3 powders under different atmospheres (air, Ar or Ar/H2 flow) was analyzed. The huge photochromic effect discovered herein was interpreted as the creation of “self-closed Schottky barrier” at the solid/solid interfaces between the two oxides, associated with the full redox reaction which can be pictured by the equation ZnO1−ε + MoO3 → ZnO + MoO3−ε. Remarkable optical contrast between virgin and color states as well as self-bleaching in dark allowing the reversibility of the photochromism is emphasized. From this first discovery, deeper characterization of the self-bleaching process shows that the photochromic mechanism is complex with a bleaching efficiency (possibility to come back to the virgin material optical properties without any deterioration) and a bleaching kinetics, which are both dependent on the coloring irradiation time. This demonstrates that the oxygen exchange through the Schottky interface proceeds in at least two convoluted steps: an anionic surface exchange allowing a reversibility of the redox reaction followed by bulk diffusion of the exchanged anions which are then definitively trapped. An emergent “negative photochromism effect” (i.e., photochromism associated with a self-bleaching instead of a darkening under irradiation) is observed after a long irradiation time.

The radiation effects of electrons and protons on the spectroscopic and optical properties of oxide glasses doped with Yb

International audience; The structural and spectroscopic properties of three Ce3+-doped A3InF6 compounds (with A+= Rb+, K+, Na+) are investigated. Containing indium, they all exhibit 2Ce3+ + In3+ ↔ In+ + 2Ce4+ redox processes induced by UV irradiation between Ce3+ and In3+ cations. The photochromo-luminescent behaviour and associated kinetics, with the Ce3+ and In+ ion emission quenching through the redox equation, respectively, are investigated. Our studies highlight that different mechanisms (surface vs. bulk) need be considered to explain the decrease in the blue (Ce3+) and orange (In+) emission curves. Moreover, the comparison of Ce3+-doped Rb2KInF6, K2NaInF6 elpasolites and K3InF6 cryolite spectral distributions shows that changing the nature of the alkali cation makes colour tuning possible. The shift of the Ce3+ and In+ colour emissions between the three as-prepared compounds is mainly due to the variation in the ionic-covalent nature of the chemical bonds around the active cation sites. The final calculated optical difference between the two bistable states varies from 0.31 to 0.48 depending on the alkali subnetwork.

International audience; Photochromism is a phenomenon describing the irradiation-induced reversible transformation of a chemical compound's colour between two states (dubbed as colour switch). This review makes an up-to-date account of inorganic photochromic compounds. In the first part, we summarise the photochromic mechanisms involving transition metal oxides, with an emphasis on the canonical WO 3 large-bandgap semiconductor. In the second part, we discuss the potential contribution of rare earth elements to the widening of the colourimetric contrasts in absorption, as well as the method of modulation in emission.

Made available in DSpace on 2022-04-28T19:41:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Horizon 2020 Framework Programme Agence Nationale de la Recherche Glass forming regions in the system GaO3/2 – GeO2 – LaO3/2 – BaO have been explored using aerodynamic levitation coupled to laser heating synthesis technique. Structure property relationships have been established between the thermal and optical properties of the resulting glass thanks to Raman and Infrared vibrational spectroscopies. The germano-gallate glass networks are mainly made of three-dimensional interconnected corner shared GeO4 and GaO4 tetrahedra forming Ge – O – Ge and Ga – O− – Ge bridges in which gallium tetrahedral GaO4 units are charged-compensated by barium and lanthanum cations. In GeO2-rich compositions, the excess of positive charges produces mainly non-bridging oxygens on germanate moieties, leading to a depolymerization of the glass network. In the case of gallium rich compositions, the infrared cut-off is red-shifted as compared to the germanate glasses, in accordance with the disappearance of germanium associated entities such as germanium and gallium bridges or germanium sites with non-bridging oxygen both vibrating at higher wavenumber. Institut de Chimie de la Matière Condensée de Bordeaux Université de Bordeaux, 87 Avenue du Dr Schweitzer Conditions Extrêmes et Matériaux Haute Température et Irradiation UPR3079 Université d'Orléans 1 Avenue de la Recherche Scientifique Institut des Sciences Moléculaires UMR 5255 Université́ de Bordeaux 351 cours de la Libération Institute of Chemistry São Paulo State University-UNESP Rua Prof. Francisco Degni, 55, CEP 14800-060 Institute of Chemistry São Paulo State University-UNESP Rua Prof. Francisco Degni, 55, CEP 14800-060 FAPESP: 2013/07793-6 FAPESP: 2019/01223-0 Horizon 2020 Framework Programme: 823941 Agence Nationale de la Recherche: ANR-10-IDEX-03-02 Agence Nationale de la Recherche: ANR-18-CE08-0004-02

We report on the 3D precipitation, using a direct laser writing approach, of highly fluorescent silver clusters in a Eu3+-doped silver-containing zinc phosphate glass. Micro-spectroscopy of fluorescence emission shows the ability to continuously adjust the local tri-chromatic coordinates in the CIE (Commission Internationale de l’Éclairage) chromaticity diagram between red and white colors, thanks to the laser-deposited dose and resulting tunable combination of emissions from Eu3+ and silver clusters. Moreover, continuous-wave and time-resolved FAST-FLIM spectroscopies showed a significant enhancement of the fluorescence emission of Eu3+ ions while being co-located with UV-excited laser-inscribed silver clusters. These results demonstrate the ability to perform efficient resonant non-radiative energy transfer from excited silver clusters to Eu3+, allowing such energy transfer to be highly localized on demand thanks to laser inscription. Such results open the route to 3D printing of the rare earth ions emission in glass.

International audience; Considering the interest to develop new photochromic compounds, the Ce doped-CaSnF6 have been selected and thoroughly characterized. After optimization of the synthesis route, the structural and morphological properties, are described. The origin of the optical properties and photochromic are supported by magnetic, RPE, 119Sn Mossbauer, 19F and 1H MAS NMR characterizations. In addition to the UV luminescence of Ce3+ ions in the stannate compound, they revealed the impact point defects at the origin of an additional visible contribution to the global signal. In view of elucidating the relationships between the observed photochromism and the possible nature of these defects, experimental interpretations are discussed on the basis of a computational approach.

Made available in DSpace on 2022-04-28T19:40:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Ho3+-doped YNbO4 and Y3NbO7 phosphors were synthesised via a co-precipitation synthesis route. Structural characterisation and spectroscopic properties were performed as a function of the Ho3+ concentration. The Rietveld type-refinement confirms the stabilisation of the pure monoclinic Fergusonite YNbO4 phase at the highest temperatures, but the quadratic phase is stabilised for the lowest temperature, whereas a pure cubic fluorite Y3NbO7 phase was observed for all of the heat treatments. Raman and infrared spectroscopies were used to compare the cation-oxygen vibrational modes. Emission spectra and up-conversion processes were obtained under excitation at 445 and 975 nm respectively. For a similar Ho3+ content, the energy transfers observed show differences between the two crystalline compounds that are related to a stronger interaction between the holmium cations in the fluorite host lattice. CNRS Univ. Bordeaux, Bordeaux INP, ICMCB, UMR 5026 ISM - Institute of Molecular Science UMR 5255 CNRS-University of Bordeaux Université de Bordeaux CNRS Laboratoire des Composites ThermoStructuraux, UMR 5801 Chemistry Institute São Paulo State University – UNESP Chemistry Institute São Paulo State University – UNESP

International audience; The effect of silicon on the natural sintering of Y3NbO7 powders is studied. Characterizations shows that Si increases densification rate and grain growth but it also leads to the apparition of a secondary silicate phase. The silicate precipitation results from the segregation of silicon favored by matter transport through a liquid phase. The distribution of the secondary phase have been studied by electronic microscopy and mapped by micro-luminescence. Thermodynamic calculations of Gibbs energy of the different phase as well as binary and ternary phase diagrams have been conducted to support interpretation of the sintering experimental results.

International audience; Mn2+-doped Zn3(PO4)2 and Mn2+-doped ZnAl2·2O4+δ compounds were prepared from solid state route and Pechini process, respectively. The luminescent properties evolution of both as-prepared powder compounds versus the annealing temperature (for 10 min annealing treatments) was studied, in the range 500–1400 °C. In parallel, Doctor Blade was used to prepare few micron-thick films for laser irradiation with the 1 μm wavelength laser of our SLS process (Selective Laser Sintering process). The ultra-rapid heating produces by laser irradiation induces on the films very different optical properties evolution in comparison to what was observed for the powder samples annealed into furnaces for the Mn-doped zinc phosphate. On the opposite, for the spinel compound, whatever the heating process (laser on film or furnace for powder samples), the modification of the luminescence properties is directly linked in a same way to the maximum temperature gained during the thermal history. The idea is to use thermal sensor to extract the temperature map of a film while it is subjected to laser irradiation as during SLS process. The study shows that thermal sensors must rely on mechanisms which remain effective even for ultra-rapid heating: a cationic redistribution versus temperature as occurring into spinel matrix is one solution proposed. But changes in the chromaticity resulting from phase transition between different allotropic forms as occurring into the zinc phosphate compound cannot be directly exploited.

Yb3+ doped oxyfluorophosphate glasses with the composition (98.75) [90NaPO3-(10-x) Na2O-xNaF] - 1.25Yb2O3 (in mol%) with x = 0, 2.5, 5, 7.5 and 10 were prepared using a standard melting process. The progressive replacement of Na2O by NaF leads to an increase in the number of Q2 units at the expense of the Q1 units. This increase in the polymerization of the glass network leads to a shift of the optical band gap to lower wavelength, to a slight increase in the intensity of the emission at 1000 nm and more importantly to a change in the glass crystallization process. Indeed, both surface and bulk crystallization were observed in the glass with x = 0 while surface crystallization only occurs when NaF is added in the phosphate network. The heat treatment leads to the precipitation of at least three crystalline phases: as x increases, the NaPO3 phase grows at the expense of Na5P3O10. All glasses precipitate the Yb containing crystal, NaYbP2O7 which leads to an increase in the intensity of the emission at 1000 nm compared to the emission at 975 nm. We show for the first time to the best of our knowledge that transparent Yb3+ doped phosphate glass-ceramics can be obtained within this glass system when free of NaF. acceptedVersion

ZnO/MoO

International audience; Rare earth niobates (RE3NbO7) are materials that present interesting magnetic [[1], [2], [3]], dielectric [4,5], photocatalytic [6,7], electric or ionic conductivity [[8], [9], [10], [11], [12]] and optical properties [13,14]. Such properties could be related to the crystal structures of RE3NbO7 that exists in three different crystalline forms depending on the ionic radii of the rare earth atoms [3,[15], [16], [17], [18], [19]]. Orthorombic (Pnma) and cubic fluorite pyrochlore (Fdm) structures are found for the largest cations, while the smallest radii RE (Dy, Ho, Er, Tm, Eu, Yb …) crystallize into a defect cubic fluorite structure (Fmm) [15,17]. Rare earth and niobium atoms are statistically distributed on cationic sites, as well as oxygen vacancies on anionic sites. This relative disordered structure leads to peculiar optical properties with a significant broadening of the 4f-4f transitions observed in an Eu-doped Y3NbO7 compound...

International audience; The spark plasma sintering (SPS) of Eu 3+-doped Y 3NbO 7 niobate phase was investigated to obtain dense ceramics. Although SPS allowed obtaining high-density ceramics, decomposition of the niobate phase occurred at high temperature and was promoted by the SPS process, which limited its use as an optical material. The niobate phase has been prepared by two synthesis methods: a solid-state route and a sol–gel method. The purity, density and microstructure of the dense ceramics were analyzed after spark plasma sintering. Translucent ceramics were only obtained from sol–gel powders after SPS at 1600 °C during 20 min with a heating rate of 5 °C/min. The sintering study of the pure niobate phase showed that during SPS process and especially in the presence of the high electrical field the Y 3NbO 7 phase is metastable at 1600 °C. A decomposition of the niobate compound is clearly demonstrated by luminescence measurements when high heating rates were used.

Made available in DSpace on 2019-10-06T17:09:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-08-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Agence Nationale de la Recherche Silver-containing glasses are promising candidates for photonic applications, due to the potentiality of spectroscopic properties of silver nanoclusters (NC's)and/or silver metallic nanoparticles. In this framework, silver-containing fluorophosphate glasses are candidates with a strong potential. Indeed, combined with femtosecond laser irradiation, silver NC's may be tailored in three-dimensional fluorescent micro-structures, whose spectroscopic properties have been investigated, revealing the creation of silver NC's but also of NP's during laser irradiation in the studied fluorophosphate glass. Additionally, the photo-inscription of silver NC's is correlatively accompanied by a positive index change, which has led to the demonstration of optical waveguiding behavior. Finally, the management of the reservoir of available silvers for laser inscription is investigated. Unlike previous observations made in standard oxide phosphate glasses, the considered silver-containing fluorophosphate glass exhibes an intriguing ability to be re-written when subjected to successive overlapping laser irradiations. Upon the optimization of compositions with tailored photo-sensitivity, the re-writable ability of fluorophosphate glasses paves the way to the design of advanced photonic devices such as photonic optical circuits, evanescent sensors or 3D high-density optical data storage. Institute of Chemistry São Paulo State University UNESP University of Bordeaux CNRS ICMCB UPR 9048, 87 avenue du Dr. A. Schweitzer University of Bordeaux CNRS CEA CELIA UMR 5107, 351 Cours de la Libération Institute of Chemistry São Paulo State University UNESP FAPESP: 2013/07793-6 FAPESP: 2016/16343-2 FAPESP: 2018/09296-3 Agence Nationale de la Recherche: N°ANR-17-CE08-0042-01

International audience; New generation of room temperature screen-printed gas sensors based on either gas sensitive semiconductive ZnO nanoparticles or on free-standing cantilevers coated with a carbon nanotube sensitive layer are herein proposed. The first type is using ZnO nanoparticles printed and sintered at 400°C on interdigitated Pt electrodes. Instead of UV LED activation giving a sensitivity improvement at room temperature, halogen lighting activation yields a good sensitivity, comparable to those given in the literature. The second type is using resonating MEMS based on piezoelectric Au/PZT/Au cantilevers coated with CNTs.. In this case, another transducing mechanism is added onto the cantilever thanks to a top interdigitated electrodes allowing both the simultaneous measurement of the resonance frequency shifts of the cantilever and the resistance variations of the resistive sensitive coating.

Made available in DSpace on 2019-10-06T15:44:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 Here, we report the luminescence properties of Yb3+/Pr3+ dual-doped fluorophosphate glasses containing silver clusters. Through the solubility of silver into the glass system as function of its initial concentration, charged species characterized as Ag+ and Agmn+ were formed and identified according to their absorption and emission spectral responses. By changing the transition metal concentration, multi-energy transfer mechanisms were observed between silver and Yb3+/Pr3+ co-doped glasses. The stabilization of silver species seems to be detrimental to the radiative processes of the rare earth ions under excitation at 444 nm (Pr3+3H4 → 3P0 absorption line). In other words, the main visible emissions of Pr3+ and the NIR emission of Yb3+ decrease with increment of Ag concentration. However, energy transfer occurs for large spectral range by the excitation of the silver species. In consequence, the visible and NIR emission could be activate in a broadband from ultraviolet to the blue part of the spectral region. These two observations highlight the competitive absorption processes and probabilities between the cationic elements and the interest to use the transition metal species as sensitizers to excite the rare earth elements. Institute of Chemistry - São Paulo State University - UNESP, CP 355 University of Bordeaux CNRS ICMCB UPR 9048, 87 Avenue du Dr. A. Schweitzer University of Bordeaux CNRS CEA CELIA UMR 5107, 351 Cours de la Liberation Institute of Chemistry - São Paulo State University - UNESP, CP 355

International audience; Properties of the tellurite glasses 80TeO2–10ZnO–[(10−x)Na2O–xAg2O] are investigated as a function of the substitution ratio x between Na2O and Ag2O. One observe that the variation of glass transition temperature decreases monotonously with x and that surface crystallization mechanism is favored. The assignment of the Raman bands and their relation with the underlying glass structure is discussed. While both Na2O and Ag2O oxides act as glass network modifiers, their progressive equimolar substitution does not lead to a meaningful evolution in the structure of the TZ[Na10-xAgx] glass. The refractive index and the cut-off wavelength are found to increase with x. The compositional and wavelength dependence of refractive indices, cut-off wavelength and optical band gap energy is discussed in terms of changes brought about by Na2O/Ag2O substitution in the glass network. Finally, it is shown that interaction between the platinum crucible and the glass melt increases with the silver content in the glass

International audience; CaSn(OH)6, CaSnO3 and CaSnF6 compounds were elaborated from a “one-batch” synthesis route: the coprecipitation of the pure double hydroxide leads to pure double oxide or fluoride after annealing treatments under air or HF as anhydrous gas, respectively. Structural and morphological features of the three matrices were carefully investigated by X Ray Diffraction analysis and Scanning Electron Microscopy, respectively. In addition, the luminescent properties of the Pr-doped compounds were performed and compared. The nanometric size of the double hydroxide inhibits the luminescence. The interpretation of the emission spectra obtained for Pr-doped CaSnO3 and CaSnF6 compounds is based on the covalence/ionic balance of the M–O or M–F bonds.

International audience; The C-form (SG: Ia[3 with combining macron]) → B-form (SG: C2/m) phase transition of RE2O3 rare earth sesquioxides is described for the first time for face centred cubic–hexagonal close-packed array transformations. Based on XRD data analysis, the temperature of the C → B phase transition in Gd2−xLaxO3 compositions (0 < x < 0.5) was controlled by adjusting the Gd/La atomic ratio and varies between 1100 °C and 1400 °C. Taking into account the various environments of rare earth oxides in C and B allotropic forms, Eu3+ was used as a local probe to obtain photoluminescence spectra (emission and excitation spectra, luminescence decay time curves). The spectra significantly changed during the phase transition, which occurred within a small temperature range. Furthermore, coupling Rietveld XRD data analysis for the long-range order signature with optical emission spectroscopy to probe the local environment provides a clear view of the C → B phase transition, allowing for the design of new highly sensitive thermal sensors at high temperatures.

Though semiconducting properties of ZnO have been extensively investigated under hazardous gases, research is still necessary for low-cost sensors working at room temperature. Study of printed ZnO nanopowders based-sensor has been undertaken for hydrogen detection. A ZnO paste made with commercial nanopowders is deposited on interdigitated Pt electrodes and sintered at 400°C. ZnO layer structure and morphology are first examined by XRD, SEM and emission/excitation spectra prior to the study of the effect of UV-light on the electrical conduction of the semiconductor oxide. Then, the response to hydrogen shows that low UV-light provided by a halogen light enhances gas sensitivity and allows detection at room temperature with sensitivity equivalent to those obtained in dark condition at 150°C. A sensitivity S≈44% is obtained for 300 ppm hydrogen at room temperature under halogen lamp illumination whereas a sensitivity S≈38% is measured at 150°C in the dark. Moreover, it is demonstrated that very low UV-light power (15 μW/mm2) provided by the halogen lamp is sufficient to give sensitivities as high as those obtained with UV LED (7.7 mW/mm2). These results are comparable to those obtained for 1 or 2D ZnO nanostructures working at room temperature or at temperature until 250 °C.

International audience; We have developed laser grade and highly Yb3+-doped cubic rare-earth sesquioxides (RE2O3, RE = Y, Gd, Lu) single crystals by means of a newly designed high-temperature solution growth method which gives them spectroscopic properties different from those obtained by high-temperature solidification methods. Absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays of the new cubic Gd2O3:Yb3+ single crystals are presented and compared to those of Y2O3:Yb3+ and Lu2O3:Yb3+ crystals. The case of cubic Gd2O3:Yb3+ is particularly interesting since its basic spectroscopic properties have never been detailed and we were capable of achieving Yb-doping level as high as 20%.

The defective fluorite-related Y

In this contribution we detail the full characterization of the anisotropy of the absorption properties of two different Yb-doped monoclinic borate compounds under polarized light. The studied crystals are Li 6 (Gd) 0.75 Yb 0.25 (BO 3 ) 3 and Li 6 Y 0.75 Yb 0.25 (BO 3 ) 3 , respectively, grown by the Czochralski method. We focused on the study of their absorption at the zero line transition as a function of the polarization direction of the incident light for two different crystal cuts of each compound. We discuss the different Eigen frames that must be considered in these materials due to their monoclinic character, as well as the optimal crystal orientation for the considered absorption and the potential influences when used as laser materials.

International audience; The defective fluorite-related Y3NbO7 host lattice was doped with Eu(3+) ions to understand the influence of spark plasma sintering (SPS) process on this host lattice. The intrinsic disorder due to the occurrence of oxygen vacancies results in amorphous-type responses of the luminescent cations, and the spectral distribution varies as a function of the niobium content. Two spectral fingerprints of europium emissions were clearly enhanced. The correlation between luminescence, X-ray diffraction, and electron diffraction characterizations shows the existence of local inhomogeneity. Indeed, the particular nonequilibrium sintering conditions allowed pointing out a lack of miscibility within the Y3NbO7 solid solution domain. Thus, the SPS pellet is a composite of two extreme compositions. This phase demixing is mainly induced by the pressure coupled with a current effect that makes possible ionic migration in this Y3NbO7 ionic conductive matrix.

International audience; First, we describe the phase diagram in between two oxides, ZnMoO4 and MgMoO4, with P-1 triclinic and C2/m monoclinic space groups, respectively. Based on the discovery of a large solid solution phase with a P-1 triclinic space group ranging from ZnMoO4 to Mg0.9Zn0.1MoO4, in this study, we investigate the potential influence of the magnesium/zinc ratio on the pigment/luminescent properties of compounds in the triclinic solid solution domain with formulae t-Mg1−x−yZnxAyMoO4, with 0.1 ≤ x ≤ 1 and with A2+ being a phosphor (Mn2+ (y = 0.01)) or chromophore cation (Co2+, Ni2+, or Cu2+ (y =0.1)). Various bright colours were obtained depending on the doping ion. Optical properties were fully interpreted by spectroscopic investigation and indexing of the absorption/excitation bands. Near white luminescence is obtained for both un-doped and Mn-doped t-Mg1−xZnxMoO4 compounds, revealing a potential use as a white source. Bright yellow, blue or pale cyan colours can be achieved using nickel, cobalt or copper as chromophores, respectively, and the colours of the t-Mg1−x−yZnxAyMoO4 are moderately impacted by the Mg/Zn ratio.

International audience; We detail the full characterization of the anisotropy of the absorption properties of two different Yb-doped monoclinic borate compounds under polarized light. The studied crystals are Li6(Gd)0.75Yb0.25(BO3)3 and Li6Y0.75Yb0.25(BO3)3, respectively, and were grown by the Czochralski method. We focused on the study of their absorption at the zero line transition as a function of the polarization direction of the incident light for two different crystal cuts of each compound. We discuss the different eigenframes that must be considered in these materials, due to their monoclinic character, as well as the optimum crystal orientation for the considered absorption and show the potential influences when used as laser materials.

International audience; Herein, diopside based glass-ceramics (GCs) were produced by sintering of glass powder compacts at 850 °C for 300 h. A special attention was paid on understanding the influence of structural transformations upon substituting strontium for calcium on the Eu3+ emission behavior. X-ray diffraction and Raman spectra showed the formation of diopside (CaMgSi2O6) in Sr-free glasses. Introduction of Sr led to the appearance of Sr-akermanite (Sr2MgSi2O7), whose formation increased continuously with increasing Sr/Ca ratio. The photoluminescence spectra exhibited intense 5D0 →7Fj transitions of Eu3+ ions. The intensity parameters (Ω2 and Ω4) and the Eu–O ligand behavior were determined using the Judd-Ofelt (JO) theory from the emission spectra as a function of various Sr concentrations. The as obtained JO intensity parameters Ω2 (5.31–5.21 pm2) and Ω4 (4.89–5.84 pm2) indicated the ligand behavior of the Eu–O bonds and a high asymmetrical and covalent environment around Eu3+ ions in the present host matrix. In comparison with other Eu3+-doped GCs, diopside based GCs containing high fraction of SrO exhibited adequate photoluminescence for optical lighting and display devices.

International audience

International audience; A Eu3+ doped Y3NbO7 niobate powder was synthetized using a polymerizable complex route. It gave rise to nanometric particles that crystallized in the fluorine structure, corresponding to the Y3NbO7 phase. The thermal evolution of this powder was followed up to 1600 °C, using X-ray diffraction and optical characterizations. The fluorine structure was maintained in the whole temperature range. However, spectral evolution of the samples calcined above 900 °C showed a more complex situation. Emission spectra of powders heat treated at different temperatures showed an evolution of the emission lines that can be attributed first to a better crystallization of the niobate phase and second to its partial decomposition in favor of the formation of YNbO4 and Y2O3. Although the Y3NbO7 phase appeared stable up to 1650 °C, from X-ray diffraction analysis, spectral analysis showed that the local environment of the doping element is modified from 1100 °C.

Absorption spectra of the Nd 3+ ions in an orthorhombic δ-BiB 3 O 6 single crystal were measured in the spectral range 11,000–20,500 cm −1 . The f–f transition intensities were analyzed in terms of the Judd–Ofelt theory, and the following parameters of the theory were obtained: Ω 2 = 6.35 × 10 −20 cm 2 , Ω 4 = 4.86 × 10 −20 cm 2 , and Ω 6 = 11.233 × 10 −20 cm 2 . The strengths, spontaneous emission probabilities, branching ratios, spectroscopic quality factor and excited state radiative lifetime were calculated for laser transitions from the 4 F 3/2 state to 4 I J manifold. Spectroscopic properties of Nd 3+ :δ-BiB 3 O 6 crystal favor lasing at 1.3 μm, where this crystal possesses near non-critical phase matching for second harmonic generation.

13 páginas, 12 figuras, 2 tablas.-- et al., A series of isostructural open-framework coordination polymers formulated as [Ln(dmf)3(ptmtc)] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5); PTMTC=polychlorotriphenylmethyl tricarboxylate) and [Ln(dmf)2H2O(αH-ptmtc)] (Ln=Sm (1′), Eu (2′), Gd (3′), Tb (4′), Dy (5′)) have been obtained by treating LnIII ions with PTMTC ligands with a radical (PTMTC3−) or a closed-shell character (αH-PTMTC3−). X-ray diffraction analyses reveal that these coordination polymers possess 3D architectures that combine large channels and fairly rare lattice complex T connectivity. In addition, these compounds show selective framework dynamic sorption properties. For both classes of ligands, the ability to act as an antenna in Ln sensitization processes has been investigated. No luminescence was observed for compounds 1–5, and 3′ because of the PTMTC3− ligand and/or GdIII ion characteristics. Conversely, photoluminescence measurements show that 1′, 2′, 4′, and 5′ emit dark orange, red, green, and dark cyan metal-centered luminescence. The magnetic properties of all of these compounds have been investigated. The nature of the {Ln–radical} exchange interaction in these compounds has been assessed by comparing the behavior of the radical-based coordination polymers 1–5 with those of the compounds with the diamagnetic ligand set. While antiferromagnetic {Sm–radical} interactions are found in 1, ferromagnetic {Ln–radical} interactions propagate in the 3D architectures of 3, 4, and 5 (Ln=Gd, Tb, and Dy, respectively). This procedure also provided access to information on the {Ln Ln} exchange existing in these magnetic systems., We thank the EU, under contract MAGMANet (no. 515767) of 6th FP, the Instituto de Salud Carlos III through “Acciones CIBER’’, the MICINN, Spain (CTQ2006-06333/BQU and CTQ2010-19501/BQU), Generalitat de Catalunya (2009SGR00516), and the Région Midi-Pyrénées in the frame of the Communauté de Travail des Pyrénées (CTP, program 2007) for funding.

International audience; We demonstrate the possibilities offered by the screen-printing technique to create thick layers of rare earth doped phosphors on glass slides for light-emitting diodes (LEDs). Using commercial LEDs, the effect of the layer thickness and phosphor concentration on luminescence emission and chromaticity are investigated. The advantages offered by screen-printed multi-phosphors systems are also revealed through a feasibility study permitting to tune the chromatic coordinate of the global light emission by modifying the phosphors characteristics independently.

5 pages; International audience; In this paper, a series of europium-activated titania mesoporous and dense thin films were prepared by sol-gel process. Structural characterizations show that high europium ion loadings can be incorporated into titanium dioxide walls with out destroy in the mesoporous arrangement. However, high europium content locks the titanium dioxide crystallization process. Upon 10% europiumions loading, mesoporous thin films are mainlyamorphous, whereas dense ones are still partially crystallized. Eu3+ ion luminescence has been investigated by exciting through the semiconductor host lattice. Emission features reveal that europiumions adopt similar environments (nano crystalline and glassy-likeones) in both dense and mesoporous thin films. Fluctuations of europium emission under continuous UV excitation have been observed. One observes that the effect strongly depends on the thin films'crystalline character which is strongly related with the texturation and existence at the mesoscopic length scale.

International audience; Single crystals of Yb doped Li6Y(BO3)3 were obtained by Czochralski method. The first laser tests were encouraging. Different parameters have been investigated to improve cw-laser performances. Thermal properties but also ytterbium content, crystal thickness and pump polarisation are reported. The best crystal configuration was determined and led to high power cw-laser tests equal to 2 W output power.

International audience; Irradiation cycling was performed to evaluate the ageing of the redox process observed on cerium-doped Rb2KInF6 compounds. An on-off switch of monovalent indium luminescence is observed for the lowest cerium doped material, whereas a nice colourimetric contrast between a bluish-green and orange emission is generated for the material with the highest cerium content. Photoluminescent properties combined with X-ray diffraction, chemical analysis and magnetism measurements allowed an accurate characterization of the system. A complete explanation of the optical behaviour is therefore proposed. Finally, printing tests were performed to illustrate the good functionality of the prepared materials for UV sensitivity.

A thorough investigation by X-ray diffraction, UV–vis and luminescence spectroscopy is carried out to demonstrate how the chromium content of alumina matrices impacts the temperature of the γ→α irreversible phase transition. The Cr 3+ contents influence slightly the phase transition temperature but control the brightness of the powders. Nice colorimetric contrasts from green to pink are observed between the two allotropic forms. Furthermore, drastic changes of the spectral distribution and of the intensity of luminescence are observed, thus allowing to use this pigment as a both thermochromic and luminescent thermal sensor. Additional measurements at low temperature revealed that the Cr 3+ emission of the γ-Al 2 O 3 matrix is constituted by a large band. A configurational diagram schematic approach suggested for the first time that this emission is due to spin-allowed 4 T 2 → 4 A 2 transition on this largely investigated γ-Al 2 O 3 compound.

Silica nanoparticles, prepared by the Stober method, have been doped with Eu 3+ , Dy 3+ , or processed to result in Au nanoparticles on the silica surface. The luminescence of the rare earth (RE)-doped SiO 2 particles has been studied as a function of the nature of the RE, their concentration and also of the presence of Au nanoparticles at the surface of the SiO 2 nanoparticles. We have shown that the Eu 3+ emission is observable over the experimental conditions examined, whereas it was not possible to observe any emission for Dy 3+ doped materials. No enhancement of the Eu 3+ emission was observed following the adsorption of gold nanoparticles at the surface of the SiO 2 nanoparticle, however an excitation at 250 nm leads to both the emission of the matrix and Eu 3+ showing an energy transfer from the SiO 2 matrix to Eu 3+ ions.

International audience; Though semiconducting properties of ZnO have been extensively investigated under hazardous gases, research is still necessary for low-cost sensors working at room temperature. Study of printed ZnO nanopowders-based sensors has been undertaken for hydrogen detection. A ZnO paste made with commercial nanopowders is deposited onto interdigitated Pt electrodes and sintered at 400 °C. The ZnO layer structure and morphology are first examined by XRD, SEM, AFM and emission/excitation spectra prior to the study of the effect of UV-light on the electrical conduction of the semiconductor oxide. The response to hydrogen exposure is subsequently examined, showing that low UV-light provided by halogen lighting enhances the gas response and allows detection at room temperature with gas responses similar to those obtained in dark conditions at 150 °C. A gas response of 44% (relative change in current) under 300 ppm is obtained at room temperature. Moreover, it is demonstrated that very low UV-light power (15 μW/mm2) provided by the halogen lamp is sufficient to give sensitivities as high as those for much higher powers obtained with a UV LED (7.7 mW/mm2). These results are comparable to those obtained by others for 1D or 2D ZnO nanostructures working at room temperature or at temperatures up to 250 °C.

In this work, both optical and electrical responses of screen-printed metal oxide gas sensors are measured under different Ar/O 2 mixtures at room temperature. Printed gas sensors are based on ZnO nanocrystals deposited and further sintered at 400 °C on interdigitated Pt electrodes. The ZnO∼5 nm nanoparticles synthetized by an organometallic route form aggregates after deposition and present surface defects observed on photoluminescence (PL) spectrum. Current and PL intensity variations are simultaneously compared under Ar/O 2 mixtures at room temperature. The sorption kinetics appear to be clearly different, with higher sensitivity for electrical conduction but unstable signal and longer time responses.

Invited talk : Mlle Véronique Jubera; International audience; In the last decades, considerable efforts have been carried out to develop new tools and knowledge in the domain of functionalized materials, for application ranging information, lighting, communication, energy, optical sources or detection. To couple an optical answer with another property is possible through the follow-up of the luminescence. The control of the structural symmetry, oxidation state or surface chemistry enables the chemists to precisely tune the emission. Illustrations will be provided on inorganic powder and crystal materials.

International audience; Mn2+ doped Zn3(PO4)2 phosphate exhibits a rich thermal history with numerous events. Following the dehydration of Zn3(PO4)2⋅4H2O hopeite at temperatures up to T = 400 °C, various allotropic forms α/δ → γ → β can be stabilized with irreversible transitions for a 600 °C ⩽ T ⩽ 1000 °C temperature range. Furthermore, in these different networks, a transition metal can occupy distorted tetrahedral (α/δ forms) and pentahedral sites as well as octahedral sites for the high-temperature γ and β forms that correspond to non-centrosymmetric environments. Depending on the thermal history of the samples, two different types of emission spectra were obtained. By increasing the annealing temperature, the green emission associated with Mn2+ in a Td environment progressively disappears in favor of the red one that corresponds to Mn2+ stabilized in fivefold and sixfold coordination sites. There is also a dependence of the emission color on the excitation wavelength arising from the differences in the excitation spectra of Mn2+ in these two types of sites. Excitations in the oxygen-manganese charge transfer band at 250 nm or in the 3d–3d absorption region at 420 nm give rise to the red or green emission at 420 nm, the green one being enhanced for an excitation at 420 nm. The α/δ → γ transition at 600 °C ⩽ T ⩽ 900 °C can easily be monitored in the emission spectra obtained after an excitation at 250 nm with a rather good chromatic contrast. The γ → β high-temperature transition at 900 °C ⩽ T ⩽ 1000 °C can be more easily followed by in the emission spectra obtained after an excitation at 420 nm. By taking into account both these emission spectra, various trichromatic coordinates can be calculated and allow subsequent phase transitions. The chromaticity of Zn3(PO4)2: Mn2+ will strongly change for 600 °C ⩽ T ⩽ 1000 °C, and one can consider this phosphate as an interesting thermal sensor.

International audience; The [(C2N2H9)VF(PO4)] compound has been synthesized by hydrothermal techniques under autogeneous pressure at 170°C. The compound was characterized from X-ray powder diffraction data with the Rietveld method. Its crystal structure consists of sheets linked by the ethylenediammonium cations and constructed by chains of VO3F2N octahedra. The thermal study indicates that the compound is stable up to 290°C. In the IR spectrum the bands of both the ethylenediammonium and phosphate ions are observed. From the reflectance diffuse spectrum the Dq and Racah parameters have been calculated. The magnetic measurements indicate the presence of antiferromagnetic interactions.