Nouvelles voies de synthèse de vanadates et de niobates luminescents au départ de précurseurs moléculaires ou hybrides
(2011)
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- Authors
- Supervisors
- Devillers, Michel
- Abstract
- (en) This research deals with the development of two unconventional preparation routes to AVO4 vanadates and ANbO4 niobates which are luminescent materials when doped with lanthanide ions. In addition, the preparation of A3NbO7 niobates was also implemented because of the great interest of such materials in the field of ion conductivity. The two developed preparation routes are based on coordination compounds which are used as precursors to incorporate the metals A, V and/or Nb. These precursors were either implemented alone in an aqueous preparation route called molecular precursors method or blended into a cellulose derivative matrix (hybrid precursor route). In this work, the two different routes were first used for the synthesis of bulk metallates and secondly for the preparation of thin films. Finally, an adaptation of the molecular precursor method was developed for the preparation of YVO4:Eu coated submicrometric silica spheres. This research has been therefore subdivided in five main parts. The first part deals with the synthesis of stoichiometrically well-defined coordination compounds of formula (NH4)A(EDTA)(H2O)x (A = Y, La, Pr, Sm, Eu, Gd, Dy, Er, Tm, Lu), (gu)3[Nb(O2)2(EDTAO2)]•2.5H2O and (NH4)[V(O)2(EDTA)]•0,5H2O. Secondly, these complexes were involved in the molecular precursor route. The method consists in using, for the different elements to be incorporated, molecular precursors which are coordination compounds. The final compound is obtained by an appropriate thermal treatment under dry air of a solid homogeneous mixture of the different complexes. This process was implemented for the preparation of bulk AVO4, ANbO4 and A3NbO7 as well as for the synthesis of solid solutions Y1-xAxVO4 and doped vanadates AVO4:Ln and Y1-xAxVO4:Eu. Luminescent properties of these doped materials were investigated and a significant effect of the host lattice composition was put forward. The hybrid precursor route was developed in the third part of this work. This method consists in the preparation of a mixed aqueous solution containing the synthesized complexes and a cellulose derivative named HPMC (hydroxypropylmethyl cellulose). After a freeze-drying step, the obtained solid is calcined under dry air to form the final metallate. After preliminary studies on the interaction between the cellulose derivative and the complexes, this route was applied for the synthesis of bulk Y1-xBixVO4 and Y1 xLaxVO4. For the Y1-xBixVO4 system, when the cellulose derivative was used, solid solutions have been obtained for a broader composition range than when the molecular precursors route was used. In the last two parts of this thesis, we focused on to the diversification of the forms in which these materials may be prepared. This research is particularly crucial for functional materials such as luminescent compounds. The two preparation routes developed above can indeed be easily adapted for the preparation of thin films by means of a spin-coating process of precursors solutions. By this way, we successfully prepared Y2O3, V2O5, YVO4 and YVO4:Eu films. In addition, the use of HPMC in the spin coated solutions appeared to improve significantly the films homogeneity. The fifth and last part of this research was dedicated to the preparation of submicrometric silica spheres coated with a layer of luminescent YVO4:Eu material. This work was motivated by the major utility of this kind of morphology for the preparation of high-performance display screens which require a high packing density. The study of the influence of this morphology on luminescence properties has also prompted us to undertake this part of the thesis. The synthesis of these coated spheres was performed by grafting an organic ligand on silica spheres prepared by the Stöber method. Y3+, Eu3+ and V4+ ions were then added and coordinated by the grafted ligand. A last calcination step has finally allowed the formation of luminescent YVO4:Eu/SiO2 spheres.
- Affiliations
Citations
Deligne, N. (2011). Nouvelles voies de synthèse de vanadates et de niobates luminescents au départ de précurseurs moléculaires ou hybrides. https://hdl.handle.net/2078.5/148377