Luminescence of silicon Dioxide — silica glass, α-quartz and stishovite

Abstract

Abstract:This paper compares the luminescence of different modifications of silicon dioxide -silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishovite mono crystal, we spectrally detected mutually similar luminescences under single-photon excitation of ArF laser. In silica glass, the luminescence of an oxygen deficient center is presented by the so-called twofold coordinated silicon center (L.N. Skuja et al., Solid State Commun. 50, 1069(1984). This center is modified with an unknown surrounding or localized states of silica glass (A.N. Trukhin et al., J. Non-Cryst. Solids 248, 40 (1999)). In stishovite, that same luminescence was ascribed to some defect existing after crystal growth. For α-quartz crystal, similar to silica and stishovite, luminescence could be obtained only by irradiation with a lattice damaging source such as a dense electron beam at a temperature below 80 K, as well as by neutron or γ-irradiation at 290 K. In spite of a similarity in the luminescence of these three materials (silica glass, stishovite mono crystal and irradiated α-quartz crystal), there are differences that can be explained by the specific characteristics of these materials. In particular, the nature of luminescence excited in the transparency range of stishovite is ascribed to a defect existing in the crystal after-growth. A similarity between stishovite luminescence and that of oxygen-deficient silica glass and radiation induced luminescence of α-quartz crystal presumes a similar nature of the centers in those materials.

The Role of Titanium Dioxide (TiO2) in the Production of Perchlorate (ClO4–) from Chlorite (ClO2–) and Chlorate (ClO3–) on Earth and Mars

“…10 The much smaller band gap of TiO 2 (anatase) (3.2 eV, ∼390 nm) compared to SiO 2 (8.5 eV, ∼145 nm) enables the reaction to utilize the UV wavelengths >300 nm with higher efficiency. 35,36 The results suggest that this role change of TiO 2 in perchlorate formation from acting solely as a UV screen under Mars conditions to photocatalyst under terrestrial conditions is caused by superoxide (O 2 − ). It has been shown that O 2 − formed at >−196 °C is not stable but that TiO 2 can stabilize O 2 − under Mars ambient conditions.…”

“…34 Because TiO 2 (anatase) has a smaller band gap (3.2 eV, ∼390 nm) than SiO 2 (8.5 eV, ∼145 nm), its ability to oxidize Cl − should be even greater than that of SiO 2 and it should still function as a photocatalyst in UVB (280−315 nm) and UVA (315−400 nm) regions where SiO 2 cannot. 35,36 Because the environments on Mars and Earth are very different, it is possible that TiO 2 could also behave very differently in each case. In this study, we determined the effects of water on perchlorate production under both dry and wet martian environments.…”

Hazai képződményekből szeparált kvarcok jellemzői az OSL kormeghatározás szempontjából

“…Ez a tendencia esetleg azzal függhet össze, hogy a kvarcban az ionizáló sugárzás hatására kristályrácshibák pl. többféle lyuk-centrum, illetve oxigénhiány centrum alakulhat ki (TRUKHIN et al 2011), amelyek nem fénykibocsátó rekombinációs centrumokat képeznek.…”

Structure and optic properties of the nanocomposites based on polypropylene and amorphous silica nanoparticles

“…10 It is also known that different modifications of the silica particles exhibit luminescence maximums in different wavelength regions. 11 The luminescence properties of silica nanoparticles in the polymer matrix was also investigated by some authors. 12,13…”

“…10 It is also known that different modifications of the silica particles exhibit luminescence maximums in different wavelength regions. 11 The luminescence properties of silica nanoparticles in the polymer matrix was also investigated by some authors. 12,13 However, there are a lot of rooms to study the structure and optical properties of polymer/silica nanocomposites, since the properties of these nanocomposites depend on the production techniques, the type of polymer, the crystallinity degree, the modification type, the size of silica.…”