Journal of Solid State Chemistry 177 (2004) 3879–3885 Origin of photoluminescence in SrTiO 3 : a combined experimental and theoretical study Emmanuelle Orhan a,Ã , Fenelon M. Pontes b , Carlos D. Pinheiro b,e , Tania M. Boschi c , Edson R. Leite b , Paulo S. Pizani c , Armando Beltra´n d , Juan Andre´s d , Jose´ A. Varela a , Elson Longo b a Instituto de Quı´mica - Universidade Estadual Paulista, Araraquara, 14801-907 SP, Brazil b Departamento de Quı´mica, Universidade Federal de Sa˜o Carlos, Sa˜o Carlos 13565-905 SP, Brazil c Departamento de Fı´sica, Universidade Federal de Sa˜o Carlos, Caixa Postal 676, Sa˜o Carlos, 13565-905 SP, Brazil d Departament de Cie`ncies Experimentals, Universitat Jaume I, PO Box 6029, AP 12080 Castello´, Spain e DCEN/CFP/UFPB, Cajazeiras, PB, Brazil Received 29 January 2004; received in revised form 19 July 2004; accepted 21 July 2004 Available online 21 September 2004 Abstract A joint experimental and theoretical study has been carried out to rationalize the photoluminescence properties of SrTiO 3 perovskite thin films synthesized through a soft chemical processing. Only the amorphous samples present photoluminescence at room temperature. From the theoretical side, first principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (ST-c) and an asymmetric (ST-a) model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of ST is discussed. r 2004 Elsevier Inc. All rights reserved. Keywords: Perovskite; Thin films; Photoluminescence; DFT; Electronic structure; Interplay theory experiment; SrTiO 3 ; Periodic calculation 1. Introduction There is much interest in the areas of science and technology in transition metal oxides with an ABO 3 perovskite structure, owing to their wide variety of unique electronic, magnetic and optical properties [1–7]. Within this class of compounds, SrTiO 3 (ST), in its crystalline form, displays a semiconductor behavior and when pure ST is excited by radiation above its energy band gap, which usually ranges from 3.2 to 3.4 eV when optically determined [8–12], a broad luminescent band appears at low temperatures [13–15]. In this paper, we show the intense visible PL spectra of amorphous ST thin films measured at room temperature. Since there, the study of PL behavior in disordered or nanostruc- tured materials [16] had focused on the development of new electroluminescent materials, owing to their poten- tial technological applications, which include flat-screen full-color displays. Our group already published numer- ous experimental studies on amorphous perovskite titanates ATiO 3 where A=Pb, Ca, Sr and Ba [17–25]. However, despite intense experimental efforts, a clear understanding of the PL behavior of ST and related ABO 3 materials has yet to emerge. Some authors propose a mechanism involving self-trapped excitons (STE) [13], others show through semi-empirical quan- tum chemical calculations that the origin of the intrinsic excitonic (‘‘green’’) luminescence of ABO 3 perovskites at low temperature would be linked to the recombination of electrons and hole polarons forming a charge transfer vibronic exciton (CTVE) [26]. ARTICLE IN PRESS www.elsevier.com/locate/jssc 0022-4596/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2004.07.043 Ã Corresponding author. Fax: +55-16-3360-8350. E-mail address: emmanuelle.orhan@liec.ufscar.br (E. Orhan).