Microwave-assisted polyol synthesis of sub-micrometer Y 2 O 3 and Yb-Y 2 O 3 particles for laser source application Marina Serantoni * , Elisa Mercadelli, Anna Luisa Costa, Magda Blosi, Laura Esposito, Alessandra Sanson Institute of Science and Technology for Ceramic (ISTEC), National Research Council (CNR), Via Granarolo 64, I-48018 Faenza (RA), Italy Received 8 May 2009; received in revised form 7 June 2009; accepted 1 July 2009 Available online 17 July 2009 Abstract Sub-micrometer powder (100–150 nm diameter) of Yb-doped yttrium oxide was obtained, for the first time, by microwave-assisted polyol (diethylene glycol, DEG) method. This method is based on fast and homogeneous increase of temperature, due to the microwave heating, and on addition of the hydrolysing agent (water) at high temperature. This promotes a fast nucleation followed by a controlled growth of nuclei. Different procedures were used to process the as-synthesized powders. In some cases washing by ultrapure water was used to dissolve nitrate and DEG by- products, this treatment allowed the use of a lower calcination temperature (150–200 8C less) to obtain the crystalline phase. Analysis of the calcined powder showed different levels of structures: from nanocrystal (10–15 nm), to primary particles (100–150 nm), to micrometer soft aggregates (2–4 mm). The microwave-assisted polyol method resulted an easy way to dope yttria with the desired amount of Yb 3+ . This work was carried out in order to prepare particles to be used as rare-earth doped Y 2 O 3 and YAG polycrystalline transparent ceramic for laser source applications. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Ceramic nanomaterials; Laser; Microwave synthesis; Polyol; Doping; Water processing 1. Introduction Synthesis of sub-micrometer non-agglomerated Yttria par- ticles is of great interest to produce devices for laser sources (Y 3 Al 5 O 12 , yttrium aluminium garnet, YAG). In view of this application, ceramic materials must have optical qualities, comparable with that of commercial high-quality doped-YAG single crystals. Unfortunately, conventional polycrystalline ceramic materials have many light-scattering centres (refractive index modulation around the grain boundary; refractive index change by inclusions or after sintering residual pores and segregation of different phases) that can affect lasing ability [1]. To decrease the derived optical loss, it is extremely important to fabricate fully dense ceramics with a pore-free structure. This can be obtained when the raw powders, that will be sintered to obtain the polycrystalline ceramic material, are non-agglomerated, of round shape and nanometric size [2–6]. The common chemical methods used to prepare nano-oxides pass through the hydrolysis of precursors salts (nitrate or organometallic species) followed by condensation and separation of a solid phase [7]. A crucial step of the synthesis is the formation of nuclei big enough to separate from the solvent in form of solid phase (nucleation). The simplest method for the generation of uniformly sized colloidal metal oxides is based on forced hydrolysis of metal salt solutions. The abrupt increasing of temperature and the controlled release of hydrolysing agent at high temperature (water) accelerate the hydrolysis and ensure a fast nucleation followed by a diffusion controlled growth of nuclei. The result is the desiderate formation of particles with an homogeneous distribution of size, shape and degree of crystallinity [8,9]. Polyol method, based on the direct precipitation in a high boiling alcohol such as DEG [10–12] with microwave-assisted heating [13–17] looks a very promising method to prepare powder for fully dense sintered materials and to easily dope yttria with the desired amount of Yb 3+ . In this paper we describe the synthesis and characterization of Y 2 O 3 and Yb 3+ doped Y 2 O 3 sub-micrometer powder from nitrate precursors by microwave-assisted polyol process. www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 36 (2010) 103–106 * Corresponding author. Tel.: +39 0546 699 732; fax: +39 0546 46381. E-mail address: marina.serantoni@istec.cnr.it (M. Serantoni). 0272-8842/$36.00 # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2009.07.002