Synthesis and Characterization of Nanoparticulate Sols of TiO 2 Doped with Erbium (III) for Photoinduced Applications
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Synthesis and Characterization of Nanoparticulate Sols of TiO2 Doped with Erbium (III) for Photoinduced Applications M. Borlaf, R. Moreno and M. T. Colomer Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049, Madrid, Spain ABSTRACT Colloidal sol-gel is a common method used for the preparation of stable and homogeneous nanoparticulate sols. In this work, TiO2 and Er3+ doped-TiO2 sols (1, 2 and 3 mole % Er3+) have been prepared. The peptization time, viscosity and isoelectric point increase at higher Er3+ concentration indicating that erbium (III) delays the peptization process, increases the viscosity and adsorbs onto the surface of the TiO2 nanoparticles. When the sols of TiO2 are doped with Er3+ lower values of the band gap are obtained. After drying, in all cases, anatase was obtained as major phase although traces of brookite are also detected. The microstructure was observed by TEM and shows direct evidence that the xerogels are polycrystalline. INTRODUCTION Titanium dioxide has been extensively studied due to its potential strength in the development of photo-electrochemical solar cells [1], photovoltaic [2] and photocatalytic systems [2-5], among many other applications. This is related to the unique properties of TiO2 including chemical resistance, low cost, easy recyclability, etc. Moreover, it can be used as a host of the lanthanide ions, such as erbium (Er3+), to obtain a photoluminescent material for its application in many fields such as wave guides, gain media for amplifiers and lasers, bio-labels, etc. Different methods of synthesis have been performed for the preparation of TiO2/Er3+ nanomaterials, the most widely used of which is the polymeric sol-gel method in non-aqueous solvent. However, sols with the highest stability must be obtained to facilitate their scaling-up for device applications. This work describes the preparation of TiO2/Er3+ nanoparticulate sols and xerogels by colloidal sol-gel route. Based on previous studies [6,7], the sols were prepared at a 50:1 water:alkoxide molar ratio and at a constant temperature of 35ºC to obtain long-term stable sols with the smallest particle size, short peptization times, and an adequate concentration. Thus, in this study, the influence of erbium (III) on the peptization process and the particle size of TiO2 sols have been evaluated. In addition, the effect of doping on the band gap of TiO2 sols has been also evaluated. EXPERIMENT Sol preparation and Characterization The alkoxide hydrolysis was carried out by adding titanium (IV) isopropoxide (97%, Sigma-Aldrich, Steinheim, Germany) to a stirring mixture of deionized water (ultrapure Milli-Q) and nitric acid (Merck, Darmstadt, Germany) in a water:alkoxide molar ratio of 50:1. In TiO2/Er3+ sol, before the addition of the alkoxide, erbium (III) acetate hydrate
(Er(OOCCH3)3•xH2O, Sigma-Aldrich, Steinheim, Germany) was dissolved in the mixture of water and nitric acid to a molar ratio Er3+/TiO2 of 1, 2 and 3 %. The temperature of the synthesis was maintained constant during the entire synthesis process
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