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1.
We report an experimental study on the photoluminescence band peaked at 2.7 eV (blue band) induced by thermal treatments in nanometric amorphous SiO2. In particular the emission dependence on the nanometric particles size as a function of their mean diameter from 7 nm up to 40 nm is investigated. We found that the emission amplitude increases on decreasing the particle diameter, showing a strong correlation between the blue band and the nanometric nature of the particles. By Raman spectroscopy measurements it is evidenced that the SiO2 nanoparticles matrix is significantly affected by the reduction of size. Basing on the shell-like model, these findings are interpreted assuming that the defects responsible for the photoluminescence are localized on a surface shell of the particles and not simply on their surface. In addition it is found that the generation efficiency of these defects depends on the structural properties of the SiO2 matrix in the surface shell. 相似文献
2.
We report the effects of γ-irradiation on the optical activity of wet synthetic silica samples. As a function of γ-dose, the growth of a composite structure in the 4–6 eV spectral region of the absorption spectrum is observed. This structure can be resolved into two main contributions centered at 5.8 and 4.8 eV, respectively. The first component is usually attributed to an optical transition of the E′ centers. The second one is able to excite an emission band centered at 1.9 eV. The analysis of the growth kinetics, in the γ-dose range 20–1000 Mrad, of both emission at 1.9 eV and absorption at 4.8 eV shows that these two bands change in a similar way, reaching constant amplitudes, after an initial linear increase, at a dose depending on the OH content. In addition, their ratio is independent of the sample. These results are consistent with a structural model in which the observed optical activity arises from a single-point defect induced by γ-irradiation. Moreover, based on the correlation with the OH content in our samples, we suggest that the principal candidate for this point defect is the non-bridging oxygen hole center (HBOHC). 相似文献
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4.
S. K. Peneva L. I. Popova E. A. Tcukeva E. D. Atanassova 《Crystal Research and Technology》1989,24(8):791-799
Microcrystalline regions of silicon dioxide with structures unobserved in the macro-state are studied by Reflection High Energy Electron Diffraction (RHEED). Their formation can be understood by considering the existence of several possible relatively stable crystalline states of SiO2, with free energies higher than those of the known silicon oxides. SiO2 with structures and lattices identical to the structures and the lattices of the CaF2-, of the rutile-type GeO2, and of α-PbO2 have been identified. Considerations for the state of silicon in some of these structures are also included. 相似文献
5.
The luminescence of silica glass, prepared by plasma chemical vapor deposition (PCVD) and quartz glass of type IV (trade mark KS-4V) methods, were studied while irradiated with pulses of ArF laser (193 nm) light in the range of sample temperatures between 10 and 300 K. The samples contain less than 0.1 ppm metallic and hydroxyl impurities. The samples synthesized by PCVD were of two kinds. The first one (amorphous) was as-deposited from plasma at a substrate tube temperature of ~1200 °C. The second one (fused) was prepared from the first by the tube collapsing with an external burner. In this process, a section of the substrate tube with the deposited glass was installed in a lathe and processed at a temperature of ~2100 °C during ~20 min until the tube was transformed to a rod. After such processing, the rod was cooled down to room temperature in air at an average rate of about 400 °C per min. The only observed luminescence possesses two broad bands, with not well defined position, one at 2.6–2.9 eV (a blue band) and another in the range of 4.4 eV (an UV band). There is a correspondence in luminescence properties between KS-4V silica and fused PCVD silica. Those bands have been attributed to oxygen deficient centers (ODC). No luminescence is observed in amorphous PCVD silica under irradiation with 193 nm laser light. So, formation of the sample by melting at least stimulates formation of ODCs at 193 nm. The blue band decays obeys to power law ~t?1 and is detected in the range of time 10 ns to 300 μs. The UV band possesses a fast, practically repeating excitation pulse, and a slow component (~30 μs). The obtained new kinetics data are compared with known in literature for lone twofold-coordinated silicon having exponential decay for the blue band equal to 10 ms and 4.5 ns for the UV band. That shows the blue band of new studied samples under ArF laser possesses decay component faster and the UV band slower than that of the twofold-coordinated silicon center. This corresponds to the recombination process of luminescence excitation by laser. We propose a model of the processes as charge separation under excitation with creation of a nearest self-trapped hole and electron trapped on the twofold-coordinated silicon, modified by its surrounding atoms or ions. This pair is recombining then with luminescence. 相似文献
6.
Q. Liu B. Poumellec X. Zhao G. Girard J.-E. Bourée A. Kudlinski G. Martinelli 《Journal of Non》2008,354(2-9):472-475
Amorphous Ge-doped H:SiO2 films on silica, deposited by matrix-distributed electron cyclotron resonance – plasma enhanced chemical vapor deposition, were irradiated with an electron beam while varying the dose. Using the Maker fringe method, second-harmonic generation was measured in the irradiated regions of the films. With a current of 5 nA, and an acceleration voltage of 25 kV for 25 s, a Ge-doped H:SiO2 film (3.8 at.% Ge) showed a maximum second-order nonlinearity of d33 = 0.0005 pm/V. In contrast, a H:SiO2 film with a smaller Ge content (1.0 at.% Ge), showed a large SHG: d33 = 0.06 pm/V when irradiated for 15 s. The second-harmonic generation in the films is caused by a frozen-in electric field induced by charge implantation from the electron beam. The strength of the electric field is determined by two conditions: the trapping centers (numbers, depth) and the remaining conductivity under large electric field. 相似文献
7.
《Journal of Non》2007,353(5-7):590-593
The applicability of the non-stationary optically stimulated electron emission (OSEE) to the spectroscopy of E′ centers in different SiO2 modifications was demonstrated. Spectral dependences of the OSEE from E′ centers in samples of silica glass, crystalline α-quartz, SiO2 films and nanoceramics exposed to fast electrons and ions were obtained. A model of the energy structure of E′ centers accounting for the absence of luminescence and taking into account the presence of two non-radiative relaxation channels (intracenter and ionization) is discussed. This model was used to substantiate the mechanism of the photothermal decay of E′ centers and to determine the quantum yields of OSEE for different types of E′ centers. 相似文献
8.
Exchange between oxygen molecules embedded in amorphous SiO2 (interstitial O2) and oxygen atoms in the a-SiO2 network is found to be remarkably slow at 500 °C. Thermal loading of 18O2 at this temperature yields a-SiO2 containing 18O-labeled interstitial O2 whose 18O fraction is as high as ~ 90%. The 18O fraction of interstitial O2 in this sample is quickly decreased by thermal annealing at or above 700 °C because of the oxygen exchange accompanied by the release of 16O from the a-SiO2 network. This finding indicates that the oxygen exchange starts at much lower temperatures than indicated by previous works, based on monitoring of the isotopic composition of oxygen atoms in the a-SiO2 network. 相似文献
9.
《Journal of Non》2006,352(36-37):3929-3935
The structure and properties of amorphous materials, in general, change with their thermal history. This is usually explained using the concept of fictive temperature, i.e., the temperature at which the super-cooled liquid state turned into a glassy state. In earlier studies, a simple IR method was used to determine the fictive temperature of silica glasses, both bulk and fiber. In the present study the applicability of the same technique for thin amorphous silica films on silicon was examined. It was found that the IR absorption as well as reflection peak wavenumber of the silica structural band can be used to determine the fictive temperature of amorphous silica films on silicon with an unknown thermal history. Specifically, IR absorbance spectra of an amorphous silica film of thickness greater than 0.5 μm grown on silicon can be taken before and after etching a thin surface layer of 20–30 nm and the peak wavenumber of the difference signal can be compared with the pre-determined calibration curve to convert the peak wavenumber to the fictive temperature. For a film thicker than ∼2 μm, IR reflection peak wavenumber can be converted directly to the fictive temperature of the film by using the calibration curve. 相似文献
10.
Optical absorption and photoluminescence of Ge-doped silica films fabricated by the surface-plasma chemical vapor deposition (SPCVD) are studied in the 2–8 eV spectral band. The deposited on silica substrate films of about 10 μm in thickness are composed as x·GeO2-(1-x)·SiO2 with x ranging from 0.02 to 1. It is found that all as‐deposited films do not luminesce under the excitation by a KrF (5 eV) excimer laser, thus indicating lack of oxygen deficient centers (ODCs) in them. After subsequent fusion of silicon containing (x < 1) films by a scanning focused CO2 laser beam absorption band centered at 5 eV as well as two luminescence bands centered at blue (3.1 eV) and UV (4.3 eV) wavelengths arise, highlighting the formation of the ODCs. The excitation of unfused SPCVD films by an ArF (6.4 eV) excimer laser yields a luminescence spectrum with two bands typical for the ODCs, but with a faster decay kinetics. Intensities of these bands grow up with samples cooling down to a temperature of 80–60 K. Unfused films excited by the ArF laser also demonstrate luminescence due to recombination of a trapped charge resulted from the excitation of localized electron states of the glass network. In the unfused GeO2 film luminescence related to a self-trapped exciton (STE) typical for GeO2 crystals with α-quartz structure is observed. The observed STE luminescence can be indicative of the crystalline fraction availability in the film. Whereas GeO2 crystals are known as not containing twofold coordinated germanium, a polycrystalline inclusion in the SPCVD GeO2 film serves as a factor explaining the absence of any spectroscopic manifestation of this type of defects in it even after fusion. On the other hand, lack of STE luminescence in other unfused films with x < 1 testifies truly amorphous state of the matter in them. 相似文献
11.
《Journal of Non》2007,353(30-31):2837-2844
The crystallization of amorphous diphasic Al2O3–SiO2 precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al2O3 preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol−1 for crystallization of Ni-containing γ-Al2O3 was obtained in non-isothermal conditions. Ni-incorporated γ-Al2O3 transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl2O4, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system. 相似文献
12.
Koichi Kajihara Taisuke Miura Hayato Kamioka Akira Aiba Motoko Uramoto Yukihiro Morimoto Masahiro Hirano Linards Skuja Hideo Hosono 《Journal of Non》2008,354(2-9):224-232
This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO2 (a-SiO2). The most common form of interstitial oxygen species is oxygen molecule (O2), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial O2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O2 in long-range oxygen transport in a-SiO2; formation of the Frenkel defect pair (Si–Si bond and interstitial oxygen atom, O0) by dense electronic excitation; efficient photolysis of interstitial O2 into O0 with F2 laser light (λ = 157 nm, hν = 7.9 eV); and creation of interstitial ozone molecule via reaction of interstitial O2 with photogenerated O0. The efficient formation of interstitial O0 by F2 laser photolysis makes it possible to investigate the mobility, optical absorption, and chemical reactions of interstitial O0. The observed properties of O0 are consistent with the model that O0 takes the configuration of Si–O–O–Si bond. Interstitial O2 and O0 react with dangling bonds, oxygen vacancies, and chloride groups in a-SiO2. Reactions of interstitial O2 and O0 with mobile interstitial hydrogen species produce interstitial water molecules and hydroperoxy radicals. Interstitial hydroxyl radicals are formed by F2 laser photolysis of interstitial water molecules. 相似文献
13.
Jun Xu Weiwei Mu Zhengyue Xia Hongchen Sun Deyuan Wei Wei Li Zhongyuan Ma Kunji Chen 《Journal of Non》2012,358(17):2141-2144
Si quantum dots/SiO2 multilayers were prepared by annealing a-Si:H/SiO2 stacked structures at 1100 °C . Photo- and electro-luminescence band around 750 nm can be observed from Si QDs/SiO2 multilayers due to the recombination of electron-hole pairs in Si QDs/SiO2 interfaces. The electro-luminescence intensity was obviously enhanced after post hydrogen annealing at 400 °C. Electron spin resonance measurements were used to characterize the change of the defect states after hydrogen annealing. It is found that there exists a-centers (g value = 2.006), which is related to the Si dangling bonds in Si QDs in our samples. Hydrogen annealing can significantly reduce non-luminescent a-centers and enhance the electro-luminescence intensity consequently. 相似文献
14.
Photoluminescence (PL) originating from intrinsic defects in neutron-irradiated crystalline (x-) SiO2 is observed and compared with that from amorphous (a-) SiO2. The PL and photoluminescence excitation (PLE) spectra of x-SiO2 are qualitatively similar to those of a-SiO2. This suggests that PL centers, similar to those found in amorphous systems, are present in ordered systems. In addition, the PL and PLE spectra a-SiO2 and a-As2S3 scale with energy band gap, suggesting that the radiative processes in a-SiO2 and semiconducting chalcogenide glasses are alike. The similarity of the PL from x-SiO2 to that from a-SiO2 and the scaling of the PL from a-SiO2 and a-As2S3 with energy band gap strongly suggest that PL centers are unique bonding configurations which primarily depend on the chemistry of the system rather than on the degree of long range order. 相似文献
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16.
《Journal of Non》2005,351(49-51):3699-3703
Thermally stimulated luminescence (TSL) properties of cerium and terbium doped SiO2 sol–gel glasses were studied after X-ray irradiation in the temperature range 10–700 K. The role of Ce3+ and Tb3+ as recombination centers was shown. The existence of a distribution of trap levels was observed; the activation energies of such a distribution were calculated to extend from about 8 × 10−3 eV up to 1.8 eV for both cerium and terbium doped sol–gel glasses. The effect of a post-densification thermal treatment on TSL properties was also analyzed. 相似文献
17.
《Journal of Non》2006,352(21-22):2152-2158
ZrO2:Eu3+–SiO2 and ZnO–SiO2 composites have been synthesized by a sol–gel method by using a specific gelation and drying procedure. In the two cases we were able to produce large and transparent monolithic samples. Microstructural properties of these materials were investigated by thermo-differential and thermo-gravimetric analysis, X-ray diffraction, transmission electron microscopy and small angle X-ray scattering. The existence of a miscibility gap in both systems results in the formation of nanocomposites where crystallized zirconia or amorphous zinc oxide nanoparticles are dispersed in a silica glass matrix. These two kinds of nanocomposites are potential high efficiency luminescent materials because the nanoparticles size is easily controlled by the annealing conditions. 相似文献
18.
The lifetime distribution of defect photo-luminescence (PL) in a-Si:H has been analyzed quantitatively by obtaining a characteristic lifetime for the distribution. The generation rate dependence and the temperature variation of the characteristic lifetime have been obtained for the defect PL. Decrease of the lifetime with increasing generation rate, i.e., the nature of non-geminate recombination, has been observed for the defect PL of 0.83 and 0.95 eV. Temperature variation of the characteristic lifetime of the PL has also been studied. The radiative recombination rate weakly depends on temperature in the case of 0.83 eV while it increases with increasing temperature in the case of 0.95–1.46 eV. Changes of the radiative recombination processes with increasing temperature are discussed. 相似文献
19.
Zhimei Yang Zhou Yu Hao Chen Zhifeng Jiao Yong Jin Yi He Min Gong Xiaosong Sun 《Journal of Non》2008,354(15-16):1731-1735
Without an additional silicon source, amorphous SiO2 nano-wires were grown on the pre-oxidized silicon substrate with the assistance of Ni-based catalyst under ambient pressure. The as-grown amorphous SiO2 nano-wires were characterized by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and selected area diffraction. The micro-region chemical composition investigation on the as-grown amorphous SiO2 nano-wires was carried out using X-ray energy dispersion spectroscopy (EDS) on the HRTEM. The present work focuses on the formation of atomic H on the surface of pure zinc powder by introducing moisture (N2 + H2O) into the furnace at high temperature. The growth mechanism has been discussed and attributed to the vapor–liquid–solid (VLS) mechanism instead of the adopted solid–liquid–solid (SLS) mechanism owing to the observed evidence of an etching reaction of atomic H at the SiO2 buffer layer and/or that of H at the Si substrate to form a gaseous hydro-silicon radical (SiHx) that is then transported to the growth sites. The intrinsic luminescent behavior of the amorphous SiO2 nano-wires in the range of 350–430 nm was also reported and discussed. These results provide an alternative and simple procedure for nanostructures growth, which will be helpful to understand the growth mechanism of one dimensional SiO2 nanostructures. 相似文献
20.
《Journal of Non》2007,353(11-12):1037-1040
Amorphous Eu2O3 was prepared by an aqueous sol–gel method. Emission due to the 5D0 → 7FJ (J = 0, 1, 2) transitions of Eu3+ ions were observed. The dominant transition was the 5D0 → 7F2 red emission of Eu3+. The properties of the as-prepared samples were different with changes in the annealing temperature. To investigate the luminescence properties of the amorphous Eu2O3, the temperature-dependent photoluminescence (PL) spectra of samples annealed at 600 °C were measured in the temperature range 77–300 K. PL peak positions were unchanged with the change of temperature. 相似文献