Search results for "SILICA"
showing 10 items of 1092 documents
Multioctave midinfrared supercontinuum generation in suspended-core chalcogenide fibers
2014
An As2S3 fiber-based supercontinuum source that covers 3500 nm, extending from near visible to the midinfrared, is successfully reported by using a 200-fs-pulsed pump with nJ-level energy at 2.5 μm. The main features of our fiber-based source are two-fold. On the one hand, a low-loss As2S3 microstructured optical fiber has been fabricated, with typical attenuation below 2 dB/m in the 1-4 μm wavelength range. On the other hand, a 20-mm-long microstructured fiber sample is sufficient to enable a spectral broadening, spreading from 0.6 to 4.1 μm in a 40 dB dynamic range.
Two-core transversally chirped microstructured optical fiber refractive index sensor
2014
We present a sensing architecture consisting of a two-core chirped microstructured optical fiber (MOF) for refractive index sensing of fluids. We show that by introducing a chirp in the hole size, the MOF can be a structure with decoupled cores, forming a Mach-Zehnder interferometer in which the analyte directly modulates the device transmittance by its differential influence on the effective refractive index of each core mode. We show that by filling all fiber holes with analyte, the sensing structure achieves high sensitivity (transmittance changes of 300 per RIU at 1.42) and has the potential for use over a wide range of analyte refractive index.
Measurement of UV-induced losses and thermal effects in photosensitive fibers using whispering gallery modes
2017
When a photosensitive (PS) fiber is exposed to UV-irradiation, a permanent refractive index change is induced in the core. As a result, according to Kramers-Kronig relations, the absorption coefficient (α) is also increased. This increment of the absorption can lead to a significant heating of the fiber when it is illuminated by a moderate optical power. Thermal effects may produce spectral changes in some fiber devices, as for example Long Period Gratings (LPGs) or Fiber Bragg Gratings (FBGs) [1].
Microstructured chalcogenide optical fibers from As2S3 glass: towards new IR broadband sources
2010
Made available in DSpace on 2013-08-28T14:12:29Z (GMT). No. of bitstreams: 1 WOS000285749500124.pdf: 1017839 bytes, checksum: f517fd8ef33fd56d66b9ccda9dc4d0f3 (MD5) Made available in DSpace on 2013-09-30T19:22:53Z (GMT). No. of bitstreams: 2 WOS000285749500124.pdf: 1017839 bytes, checksum: f517fd8ef33fd56d66b9ccda9dc4d0f3 (MD5) WOS000285749500124.pdf.txt: 33157 bytes, checksum: 1ca2ac713bf6024674249abf58520bcb (MD5) Previous issue date: 2010-12-06 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:34:00Z No. of bitstreams: 2 WOS000285749500124.pdf: 1017839 bytes, checksum: f517fd8ef33fd56d66b9ccda9dc4d0f3 (MD5) WOS000285749500124.pdf.txt: 33157 bytes,…
Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers
2010
Made available in DSpace on 2013-08-28T14:10:10Z (GMT). No. of bitstreams: 1 WOS000275454100017.pdf: 273411 bytes, checksum: da2aeaea61ab57013d39ecf2456466e3 (MD5) Made available in DSpace on 2013-09-30T19:22:36Z (GMT). No. of bitstreams: 2 WOS000275454100017.pdf: 273411 bytes, checksum: da2aeaea61ab57013d39ecf2456466e3 (MD5) WOS000275454100017.pdf.txt: 34647 bytes, checksum: b4efba760b21442eba43e7096f213b3e (MD5) Previous issue date: 2010-03-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:33:52Z No. of bitstreams: 2 WOS000275454100017.pdf: 273411 bytes, checksum: da2aeaea61ab57013d39ecf2456466e3 (MD5) WOS000275454100017.pdf.txt: 34647 bytes, ch…
From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling
2015
Abstract It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca 4 H 4 Si 5 O 16 , Ca 2 H 2 Si 2 O 7 and Ca 6 (HSi 2 O 7 ) 2 (OH) 2 , respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups v…
Effect of NiO and/or TiO2 mullite formation and microstructure from gels
1998
Polymeric and colloidal gels with a constant molar ratio of (Al+Ni and/or Ti)/Si=3/1 and various (Al/Ni and/or Ti) ratios (up to 21.42 mol% NiO+TiO2) were prepared and used to study the effect of the precursor chemical homogeneity on mullite formation processes and the resulting microstructure. Both kinds of gel precursors were preheated at 750°C for 3 h in order to obtain appropriate gel-derived glasses for further thermal processing. After annealing for several time periods at temperatures between 750 and 1500°C, differences in crystallization pathways were observed. Polymeric gels crystallized Al–Si and NiAl2O4 spinels from the amorphous form at temperatures in the range between 900 and …
High-efficiency silicon-compatible photodetectors based on Ge quantum dots
2011
We report on high responsivity, broadband metal/insulator/semiconductor photodetectors with amorphous Ge quantum dots (a-Ge QDs) as the active absorbers embedded in a silicon dioxide matrix. Spectral responsivities between 1-4 A/W are achieved in the 500-900 nm wavelength range with internal quantum efficiencies (IQEs) as high as ∼700%. We investigate the role of a-Ge QDs in the photocurrent generation and explain the high IQE as a result of transport mechanisms via photoexcited QDs. These results suggest that a-Ge QDs are promising for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget. © 2011 Amer…
Cyclam-functionalized silica-modified electrodes for selective determination of Cu(II)
2009
Cyclam derivatives have been grafted via 1, 2 or 4 silylated arms to the surface of mesoporous silica and the resulting materials have been incorporated into carbon paste electrodes and applied to the preconcentration electroanalysis of Cu(II). Sensitive and selective detection of the target analyte was achieved owing to the attractive binding properties of this macrocyclic ligand towards Cu(II) species. Various parameters likely to affect the preconcentration and detection steps have been studied, including pH of the accumulation medium, composition of the detection solution, structure and composition of the adsorbent, accumulation time, or presence of potentially interfering species. In p…
Comparison of silica-based materials for organophosphorus pesticides sampling and occupational risk assessment.
2020
Abstract A novel air sampler has been designed containing a sorbent based on UVM-7 mesoporous silica doped with Ti. The sorbent has been applied for the determination of organophosphorus pesticides in occupational air, followed by gas chromatography with mass spectrometry detection. Thus, several silica materials with different structures (mesoporous UVM-7 and microporous xerogels) were synthesized, and modified with the addition of Ti and Fe. The structure of these materials was proved by transmission electronic microscopy, energy-dispersive X-ray, X-ray diffraction, nitrogen adsorption-desorption and UV–Vis and Raman spectroscopy. The potential of these materials for the retention of pest…