Laser stimulated light reflection for TeO 2 –WO 3 –Bi 2 O 3 thin films with incorporated Si nanoparticles L.R.P. Kassab a , M.E. Camilo b , T.A.A. de Assumpção b , G.L. Myronchuk c, ⁎ a Laboratório de Tecnologia em Materiais Fotônicos e Optoeletrônicos, Faculdade de Tecnologia de São Paulo, CEETEPS/UNESP, São Paulo, SP, Brazil b Departamento de Engenharia de Sistemas Eletrônicos, Escola Politécnica da USP, São Paulo, SP, Brazil c Eastern Ukrainian University, Solid State Physics, Voli 13, Lutsk, Ukraine abstract article info Article history: Received 8 April 2013 Received in revised form 15 May 2013 Available online 15 June 2013 Keywords: Photoinduced optical effects; Optical features of nanoparticles A novel method of preparation of the Si nanoparticles (NPs) incorporated in tellurite TeO 2 –WO 3 –Bi 2 O 3 (TWB) thin films is proposed. This mew method applies RF magnetron sputtering technique at room temper- ature. The incorporation of Si NP was confirmed by transmission electron microscopy (TEM); isolated Si NPs with diameters of around 6 nm are observed. Energy dispersive X-ray spectroscopy (EDS) was performed during TEM analysis in order to confirm the presence of Si NP and also the other elements of the thin film. The thin films are explored with respect to the photoinduced changes of the reflectivity within the 400–65 nm spectra range using a 10 ns pulsed Nd:YAG with power densities varying up to 400 MW/cm 2 and beam diameter within the 3–5 mm range. The observed processes are analyzed within a framework of trapping level conceptions for the Si NP. The possible application of the discovered materials as optical sen- sitive sensors is proposed. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Silicon nanoparticles (Si-NPs) are of interest because of their pos- sible applications in biomedical and medical fields [1]. Researches performed on Si NP were focused on their luminescent/fluorescent features [2], optical limiting capability [3], and their use as nanoparticle- embedded optical waveguide materials [4]. A detailed analysis of the interaction between light and Si NP was given in Ref. [5]. Complex studies including photoluminescence spec- tra, ellipsometry, and Raman spectroscopy as well as Z-scan tech- nique have unambiguously shown a difference between the surface and bulk contributions. However, the use of the SiO 2 matrix as a ma- trix for Si NP has a drawback because it does not possess high polar- izable heavy elements. First of all it would be interesting to perform the studies of their properties for the oxide matrices with heavy high polarizable ions like Bi, Te, and W. The existence of such ions should be manifested in the enhanced photoinduced electron–phonon interactions [6]. Multi-exciton generation (MEG) plays a fundamental role. The crea- tion of more than one electron–hole pair per photon absorbed [7], which effectively interacts with the phonon sub-system [8], changes their linear as well as nonlinear susceptibilities [9]. Using atomistic pseudopotential simulations in Ref. [10] it was established that in oxide matrices there exists two specific types of distorted bonds: Si\Si and bridging Si\O\Si bonds between two Si atoms near the Si NP surface. Moreover, a band structure calculation analysis of opti- cal absorption spectra assumes that the Si NPs are affected by quan- tum size effects [11] and have the nature of an indirect-band-gap semiconductor. All these arguments indicate that their photoinduced properties should be substantially different with respect to the pure films [12]. The results performed for the silicon-oxynitride films show substantial importance for the multi-photon processes which can change the total view of the transmission and the related light re- flection [13]. As a consequence in the present work we have chosen the 54.6 TeO 2 –22.6 WO 3 –22.8 Bi 2 O 3 (wt.%) thin film with Si NP. Tellurite glasses are excellent materials for photonics applications because of their high refractive index (~2.0), large transmittance window (360–5000 nm), low cutoff-phonon energy (700 cm -1 ), large mechanical resistance, high chemical durability, high vitreous stability, and high solubility for rare-earth ion doping species. As a photoexciting beam we have used the second harmonic generation of Nd:YAG 532 nm laser which has shown its efficiency during stud- ies of the different oxide films [14]. And as a probing (sensing) tool it was used to reflect light similarly to the method described in Ref. [15]. The studies were performed within the spectral wavelength range of 400 nm–700 nm, where one can expect the principal changes of the reflected spectra [16–18]. Optical transitions of Er 3+ /Yb 3+ codoped TeO 2 –Bi 2 O 3 –W0 3 glass were reported recently [19] and provided important information for further development of Er 3+ doped materials for broadband ampli- fiers and upconversion lasers. Studies of the high refractive index and of the diamagnetic properties of TeO 2 –WO 3 –Bi 2 O 3 glasses were also published [20]. Second harmonic signals have been successfully Journal of Non-Crystalline Solids 376 (2013) 90–93 ⁎ Corresponding author. Tel.: +380 322708264. E-mail address: galynamyronchuk@yahoo.co.uk (G.L. Myronchuk). 0022-3093/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2013.05.033 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol