Thermal stability and optical property of ormocers (organically modified ceramics) nanoparticles produced from copolymerization between amino-silanes and tetraethoxysilane M. Jafarzadeh a, b, ⁎, R. Adnan c , M.K.N. Mazlan c a Faculty of Chemistry, Razi University, 67149‐67346 Kermanshah, Iran b Nanoscience and Nanotechnology Research Center, Razi University, 67149‐67346 Kermanshah, Iran c School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia abstract article info Article history: Received 12 May 2012 Received in revised form 22 July 2012 Available online 10 August 2012 Keywords: Aminopropyl-modified silica; Nanoparticles; Optical properties; Photoluminescence; Co-condensation The effect of heat treatment on the optical activity of ormocers (aminopropyl-modified silica) is studied using photoluminescence and ultraviolet diffuse reflectance spectroscopy techniques. The thermal stability of the modified silica is also investigated by X-ray diffraction and thermogravimetric analyses. Great withstanding of aminopropyl group located inside the silica network is found at high temperature. Distinct blue and green bands are observed in the modified silica nanoparticles after heat treatment using different temperatures, whereas some optical activities in the area of near-ultraviolet and infrared relating to the OH-related and carbon-related species and non-bridging oxygen hole center, respectively, diminished. The decrease in the band intensity besides band shift was evidences for changing the structural defect owing to releasing and decomposing of aminopropyl group from the nanoparticle surface. Some ultraviolet bands were detected be- cause of the existence of oxygen-related defect. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Intriguing optical properties have been found in nano-sized silica particles due to some surface defects on the particle surface [1]. Dehy- dration of physisorbed water and dehydroxlation of vicinal hydroxyl groups by heat treatment generally give rise to some point defects in otherwise perfect silica network. Although organo-modification of nanosilica surface with organosilanes can efficiently enhance the dispersity of nanoparticles but it may lead to some further struc- tural imperfection due to the presence of organosilanes [2]. A varie- ty of structural defects was documented in literature for silica nanoparticles such as surface E′ centers (`Si·Si` or `Si•), non- bridging oxygen hole centers (NBOHC; `Si\O•), oxygen deficient centers (ODCs; `Si\Si`), two-fold coordinated silicon lone pair centers (`Si\O\Si\O\Si`), silanone (O_Si_O), dioxasilyrane (_SiO 2 ) and silylene (_Si:) centers, peroxy linkage (`Si\O\O•), hydrogen-related species (`Si\H and `Si\OH) and interstitial O 2 molecules [3–7]. Glinka et al. reported that photoluminescence (PL) activity (peak intensity and peak shift) is extensively a func- tion of heat treatment temperature leading to the formation of structural defect [8,9]. Furthermore, post-treatment and annealing showed a direct influence on the nature of surface defect points [10,11]. In our previous work, aminopropyl-modified silica nanoparticles were prepared via an efficient co-condensation method [12]. By ap- plying this technique, the interior and exterior of the bulk of silica particle was homogeneously modified by organic functional group which showed better physical and optical properties compared to the modified silica prepared in post-modification process [13]. Sever- al bands such as blue, green, and red optical bands related to the de- fect centers such as E′ centers, oxygen deficient center, self-trapped exciton, OH-related surface defect, hydrogen-related species and carbon-related species were observed in broad range, from near-IR to UV [14]. In the present work, the effect of heat treatment on the optical re- sponse of aminopropyl-modified silica was studied using room temper- ature PL and UV diffuse reflectance spectroscopy (DRS) techniques. The XRD, TGA and TEM were employed to study the stability of the modified silica structure upon thermal process. The samples underwent calcina- tion at different temperatures (300, 400, 500, 700 and 900 °C) in fur- nace for 2 h. 2. Experimental 2.1. Procedure for modification of silica nanoparticles via co-condensation method A mixture of 4 mL of tetraethoxysilane (TEOS) and 1 mL of γ-aminopropyltriethoxysilane (APTES) in 30 mL of absolute ethanol Journal of Non-Crystalline Solids 358 (2012) 2981–2987 ⁎ Corresponding author. Fax: +98 831 427 4559. E-mail address: mjafarzadeh1027@yahoo.com (M. Jafarzadeh). 0022-3093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2012.07.028 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol