Solar parameters of induced WO 3 -coated glass Nilgu ¨n Dog ˘an Baydog ˘an a , Esra O ¨ zkan Zayim b, * , A. Beril Tug ˘rul a a Istanbul Technical University, Institute of Energy, Ayazaga Campus, 34469 Istanbul, Turkey b Istanbul Technical University, Science and Literature Faculty, Ayazaga Campus, 34469 Istanbul, Turkey Received 18 June 2007; received in revised form 27 August 2007 Available online 15 September 2007 Abstract WO 3 ﬁlms were prepared by sol–gel deposition process on Corning 2947, microscope slide substrates. The eﬀects of irradiation on the solar parameters of WO 3 ﬁlms were investigated between 1 and 21 kGy absorbed dose by Co-60 radioisotope. Three characteristic optical density bands explained the causes of color due to the absorption of sunlight at induced color centers of the transition elements such as W, Fe and Zr after the gamma irradiation. These bands lead to variations on the solar control in terms of shading coeﬃcient. The absorbed dose plays a key role in the improvement of the shading coeﬃcient dramatically, hence the solar parameters changed considerably depending on the induced color centers of the transition elements and the variations of the grains and the void sizes of the ﬁlm. The results of the solar parameters of irradiated WO 3 ﬁlms were compared with the unirradiated WO 3 ﬁlms and uncoated corning in the solar range. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.80.x; 68.55.a; 81.15.Aa; 96.60.Tf Keywords: Co-60; Film deposition; Solar properties; Tungsten oxide; Thin ﬁlms 1. Introduction Some transition metal oxides exhibit variable optical properties. Thin ﬁlms of these transition metal oxides are being pursued as vital components in switchable devices [1]. Tungsten oxide ﬁlms are of much interest for applica- tion as working electrochromic layers in electrochromic devices. Its advantages are high coloration eﬃciency and relatively low price [2]. The solar control in vehicles glazing with diﬀerent types of ﬁlms is an important task for several purposes and appears to be a growing global trend [3]. Besides, adjustable surface emissivity devices are of interest for smart temperature controlling. The spectral region, in which the emissivity of the device has to be controlled, depends on the temperature of the surface. Thermal con- trol of satellites is accomplished by balancing the energy dissipated by satellite electrical components against the energy emitted as IR radiation [4–6]. Coated glass materi- als can be used broadly in space vehicles depending on their optical and solar performances of them. However, the devices that consist of WO 3 ﬁlms on satellites and space shuttles can be aﬀected especially by gamma irradiation as the cumulative dose during their space missions. Under irradiation, the defect centers in these glass materials are formed as a result of charge trapping by radiolytic elec- trons or holes. One of the essential processes occurring during the irradiation of the samples is the formation of electron–hole pairs. These free carriers can move and recombine so that the photoelectrons are trapped at struc- tural defects or impurities, such as oxygen vacancies and multivalent impurities, while the holes are self-trapped at bridging or non-bridging oxygens. These new electronic conﬁgurations give rise to some preferential high absorp- tion levels called color centers [7–9]. Surface radiation emission at room temperature (26.85 °C) occurs in the infrared spectral region and satellite emittance can be characterized by a blackbody spectrum at room temperature degree. IR-emittance modulation devices are of interest for their thermal control in satellites 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.09.024 * Corresponding author. Fax: +90 212 285 63 86. E-mail address: ozesra@itu.edu.tr (E. O ¨ zkan Zayim). www.elsevier.com/locate/nimb Available online at www.sciencedirect.com Nuclear Instruments and Methods in Physics Research B 264 (2007) 302–310 NIM B Beam Interactions with Materials & Atoms