Silica nanoparticle core structure examined by the E′Siγ center 29Si strong hyperfine interaction

The Relevance of Point Defects in Studying Silica-Based Materials from Bulk to Nanosystems

“…A possible explanation of this difference was reported by Buscarino et al in [105] studying the behavior of Si-E´γ hyperfine doublet signal. Similarly, the hyperfine lines separation was used to investigate the structure of the inner part of the silica nanoparticles both with respect to the bulk silica and as a function of the nanoparticles' sizes [35]. One of the main results of this study was to support the core shell model for silica nanoparticles in which the core and the surface shell structures are different and independent from the nanoparticles' size [30,[33][34][35][36][37][38][39][40].…”

“…Subsequently, [31,32] have supported the differences between these two parts of the nanoparticles by employing structural investigation techniques such as Raman scattering [31], but also studying the properties of point defects performing electron paramagnetic resonance (EPR) experiments [32]. Then, to support the independence from the nanoparticle sizes, systematic studies were performed on particles going from average diameters of 7 to 40 nm [33][34][35][36][37][38][39]. The emission and the Raman signal of interstitial oxygen molecules [33,34] were studied showing that these molecules are present in the core, whereas the surface (rich of OH groups [33]) is unable to retain these small molecules.…”

“…The emission and the Raman signal of interstitial oxygen molecules [33,34] were studied showing that these molecules are present in the core, whereas the surface (rich of OH groups [33]) is unable to retain these small molecules. The density of the core was proved to be slightly higher (~4%) [35] than that of bulk silica, using the relation between density and some EPR spectral features of the E'Si [6] (see paragraph 4). Such a result, in agreement with the simulation [30], was supported by the Raman data [36].…”

“…Furthermore, the concentrations of defects such as E´Si, NBOHC (non-bridging oxygen hole centers) [6], and others were used to investigate other properties of the nanoparticles [33][34][35][36][37][38][39][40][41]. From the data reported in [33][34][35][36][37][38], the surface shell thickness was estimated to be ~1 nm, and it was also characterized by studying the visible emission related to surface point defects [38][39][40][41].…”

“…A clear example of this is constituted by the Si-OH defects for telecommunication fibers [27] and nanoparticles [13,28,29]. [1,2]; (b) Scheme of a silicon-on-insulator (SOI) according to that reported in [2]; (c) Optical fiber basic representation with core and cladding; (d) Scheme of a silica nanoparticle with some of the characteristics obtained in [30][31][32][33][34][35][36][37][38][39][40][41].…”