Eu 3+ -Doped Y 2 O 3 -SiO 2 Nanocomposite Obtained by a Sol-Gel Method

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Eu3+-Doped Y2O3-SiO2 Nanocomposite Obtained by a Sol-Gel Method Carla Cannasa, Mariano Casua, Roberta Licheria, Anna Musinua, Giorgio Piccalugaa, Adolfo Speghinib and Marco Bettinellib a Dipartimento di Scienze Chimiche, Università di Cagliari, SP Sestu-Monserrato, Km 0.700, I-09042 Monserrato, Cagliari, Italy b Dipartimento Scientifico e Tecnologico, Università di Verona, Ca' Vignal, Strada Le Grazie 15, I37134 Verona, Italy

ABSTRACT A Y2O3-SiO2 nanocomposite doped with Eu3+ was obtained by a sol-gel method and characterized by X-ray diffraction, IR, 29Si NMR and laser-excited luminescence spectroscopy. It was found that small (2-3 nm) yttria nanoparticles are homogeneously dispersed in, and interacting with, the amorphous silica matrix. Luminescence spectroscopy indicates that the Eu3+ ion is preferentially located inside or at the surface of highly disordered Y2O3 nanoparticles. These luminescent nanocomposites form a class of materials which could find applications in the field of phosphors. INTRODUCTION Lanthanide ions in insulating host matrix find uses in a wide variety of applications, such as phosphors for fluorescent lighting, display monitors, X-ray imaging, laser and amplifiers for fiber–optic communication. Preparing nanoscale host materials can change the physical properties, which affect the luminescence and dynamics of the optically active dopant. Nanocrystalline Y2O3 has been investigated as a host, due to its interesting applications in the field of the phosphors for lighting and for cathode ray tubes 1,2. In the present work, we decided to investigate the optical properties of Eu3+ doped Y2O3 nanoparticles dispersed in a transparent medium such as amorphous SiO2, which can stabilize and protect the nanoparticles from aggregation 3. The Eu3+ ion was chosen on the basis of its high emission quantum yield, its relatively simple energy level scheme, its applications as structural probe for the sites occupied by the Ln3+ in a given material, 4 and the technological importance of Y2O3:Eu3+ as a phosphor 2. The present study focuses on the preparation, the characterization of structural and optical properties of a Eu3+-doped Y2O3-SiO2 nanocomposite, containing 10 wt% of Y2O3, obtained by a sol-gel method which involves the use of the nitrate salt as precursor 5. This procedure in principle favors the formation of metal oxide nanoparticles hampering the embedding of metal ions in the silica matrix amorphous network6. This work may also lead to an easy, effective preparation method for these materials. EXPERIMENTAL An Eu3+-doped Y2O3-SiO2 nanocomposite containing 9.8 wt% of Y2O3 and 0.2 wt% of Eu2O3 (corresponding to an Eu/Si atomic ratio of 7.6⋅10-4) was prepared by a sol-gel method following the procedure described elsewhere 7. An aqueous solution of weighted amounts of yttrium and europium nitrate (Y(NO3)3·6H2O and anhydrous Eu(NO3)3, Aldrich 99%) was mixed with an ethanolic solution of tetraethoxysilane (EtOH 95%, TEOS, Aldrich 98%) and acidified with nitric acid up to pH