Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol–gel nanofilms A. Ferreira da Silva a, * , I. Pepe a , James L. Gole b , S.A. Toma´s c , R. Palomino d , W.M. de Azevedo e , E.F. da Silva Jr. f , R. Ahuja g , C. Persson h a Instituto de Fisica, Universidade Federal da Bahia, Campus Ondina, 40 210-340 Salvador, BA, Brazil b Schools of Physics and Mechanical Engineering, Georgia Institute of Technology Atlanta, GA 30332-0430,USA c Departamento de Fı ´sica, CINVESTAV-IPN, AP 14-740, Me´xico D.F. 07300, Mexico d Facultad de Ciencias Fı ´sico-Matema´ticas, BUAP, AP 1152, Puebla, Mexico e Departamento de Quimica Fundamental, Universidade Federal de Pernambuco, Cidade Universitaria, 50670-901 Recife, PE, Brazil f Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, 50670-901 Recife, PE, Brazil g Department of Physics, Uppsala University,SE-751 21 Uppsala, Sweden h Department of Materials Science and Engineering, Royal Institute of Technology SE-100 44 Stockholm, Sweden Available online 20 January 2006 Abstract In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO 2 ) as nanofilms prepared by the sol–gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO 2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eVattributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO 2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO 2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO 2 films prepared for undoped sol–gels and by sputtering is performed. # 2006 Elsevier B.V. All rights reserved. PACS: 71.15.Mb; 71.20.Nr; 78.20.ci; 81.40.Tv Keywords: Polymer; TiO 2 nanofilms; Electronic band structure; Rhodamine 6G doping 1. Introduction TiO 2 is a promising oxide for the fabrication of thin dielectric films used in dynamic random access memory (DRAM), storage capacitors and as gate dielectrics for metal- oxide-semiconductor field effect transistors (MOSFET) [1]. TiO 2 nanoparticles might serve as an excellent source for the photocatalytic decomposition of organic pollutants in water. Currently, however, the highly efficient use of TiO 2 in photocatalysis applications is prevented by its wide bandgap (3.2 eV), which responds to only a small fraction of the sun’s energy spectrum. Thus, one of the goals to improve the performance of TiO 2 is to increase its optical activity by shifting the onset of its response from the UV to the visible region [2,3]. Here we will present spectroscopic properties of doped and undoped TiO 2 as nanofilms prepared by the sol–gel process, including rhodamine 6G doping during film prepara- tion, studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO 2 thin films doped with, for example, rhodamine 6G at very low concentration show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eVattributed to TiO 2 absorption. The optical absorption and band gap energy for the rutile phase of titanium dioxide are calculated employing a fully relativistic, full-potential linear- ized augmented plane-wave (FPLAPW) method [4] within the local density approximation (LDA). The LDA is improved by www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5365–5367 * Corresponding author. Tel.: +55 71 3263 6647; fax: +55 71 3263 6606. E-mail address: ferreira@venus.fis.ufba.br (A.F. da Silva). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.041