Study on characteristics of silicon nanocrystals within sol–gel host (original) (raw)
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Properties of Luminescent Si Nanoparticles in Sol-Gel Matrices
Journal of Sol-gel Science and Technology, 1998
In this wor e preparation and properties of silica sol-gels incorporating luminescent Si nanocrystallites extracted from porous Si are described for the first time. These sol-gel/Si nanocrystallite composite materials are characterized by BET isotherm measurements, photoluminescence spectroscopy, and infrared spectroscopy. To stabilize the photoluminescence (PL) of Si crystallites within the silica matrix, a fatty acid (capric (C10), myristic (C14) or arachidic acid (C20)) is added as a passivation agent during the hydrolysis of tetraethoxysilane. The presence of the fatty acid is crucial to the long-term stability of the Si nanocrystallite luminescence, as the Si visible light emission remains essentially unchanged for more than a month when the fatty acid is present in the mixture but degrades quickly (within days) when absent. The thermal stability of the Si luminescence within the sol-gel is also reported. Fluorescence microscopy reveals that the light-emitting Si crystallites aggregate into micron-sized domains somewhat unevenly throughout the silica matrix. This distribution of Si crystallites can be improved by employing a surfactant, dioctyl sodium sulfosuccinate (DSS).
Photoluminescence properties of sol–gel derived SiO2 layers doped with porous silicon
Materials Science and Engineering: C, 2002
. We proposed and studied a new light emitting material based on silicon nanocrystals Si-nc . The new material was fabricated using a Ž . low cost way by incorporating Si-nc into a sol-gel derived SiO matrix. The Si-nc were prepared i by electrochemical etching of 2 Ž . monocrystalline Si wafers and ii pulverizing the obtained porous silicon film. The porous silicon powder was then dispersed in the SiO 2 sol. After solidification, we obtained transparent and self-supporting SiO layers of about 1 mm thickness containing Si nanocrystals. The 2 Ž . sol-gel layers exhibit bright red photoluminescence PL under UV lamp excitation at room temperature. This novel method circumvents the usual Si q -implantation step. We present first basic experimental studies of the PL properties of these sol-gel derived SiO layers and 2 compare them with that of as-prepared porous silicon. We mention also observation of a non-linear behavior in the PL spectra. We emphasize potential advantages of this technology compared to the standard Si q -implanted SiO layers. q 2002 Elsevier Science B.V. All 2 rights reserved.
Si-nanocrystals/SiO2 thin films obtained by pyrolysis of sol–gel precursors
Thin Solid Films, 2008
Polymer pyrolysis to nanoceramics is employed for the production of photo-luminescent thin film samples, consisting of Si-nanocrystals dispersed in silica matrix. Thin films were deposited on Si wafer by spin-coating technique from a triethoxysilane-derived sol-gel solution. This is a fast process and a low cost technique. Samples were annealed at different temperatures between 600°C and 1300°C, under N 2 gas atmosphere. Structural evolution and luminescence from Si-ncs vs. temperature were investigated by FT-IR absorption spectroscopy and photo-luminescence. Absorption spectrum of As-Prep sample shows several vibrational bands due to Si-H, C-H x , and Si-O-Si structural units, without any appreciable luminescence. Silica phase segregation and intense PL (790 nm) due to Si-ncs were observed on annealing at T N 1000°C.
Characterisation of silicon nanocrystals in silica and correlation with luminescence
Nanocrystalline silicon emits visible light (1.7eV) even though bulk Si has an indirect bandgap in the infra-red region. Si nanocrystals have been produced by ion implantation into an amorphous silica substrate followed by annealing at 1050 degrees Celsius. It was observed that the wavelength and intensity of emission is dependent on the ion implantation dose, annealing time and annealing temperature and is presumably related to the particle distribution. The mechanism for emission in such nanocrystals is as yet only partly understood, although recent results suggest interplay between quantum confinement and interface defect states.
Photoluminescence characterization of sol–gel prepared low density silica samples
Journal of Non-crystalline Solids, 2007
By exciting with synchrotron radiation in the 4–10 eV range the emission properties of sol–gel synthesized porous silica at room temperature and at 8 K are investigated. The modifications of the ultraviolet emission in the range 3.7–4.2 eV excited at different energies (5.64, 6.20, 6.53, and 6.89 eV) support the hypothesis of the contribution of two emitting centers. In particular the two emissions are spectrally resolved when exciting at 5.64 eV and a blue shift of the emission peak is reported as the excitation energy increases. The analysis of the decay times indicates that the two centers are temporally resolved with the 5.64 eV excitation both at room temperature and at 8 K and allows to estimate lifetimes of about 3 and 18 ns. When exciting at 6.53 eV, the larger relative contribution of the 4.0 eV band does not allow to efficiently resolve the two decay times and the estimated life time of the 3.8 eV band is shortened.
Journal of Sol-Gel Science and Technology, 2014
This work reports on the mechanisms behind the sol-gel synthesis and versatile luminescent behavior of sol-gel silica-based materials based on hexamethoxydisilane (Hexamet) or hexaethoxydisilane (Hexaet) innocuous monomers, at different annealing temperatures. The resulting as-synthesized materials exhibit an intense photoluminescence (PL) band in the blue region of the spectrum, whose maximum shifted in the region of 430-650 nm by applying an annealing process at different temperatures in the range of 350-1,000°C. This behavior could be attributed to the presence of different silica matrix defect-related luminescent mechanisms. PL emission bands of the Hexamet-derived materials prepared at higher T up to 1,300°C slightly shifted and appeared in the region of 400-700 nm. However, those Hexaet-derived materials annealed at T between 1,000-1,150°C showed bands peaking at and above 800 nm, these being related to a quantum confinement effect induced by the presence of silicon nanocrystals (Si_nc) within the polymer matrix. Based on studies carried out by different microscopy and chemical analysis techniques, the origin of the PL behavior was attributed to the kinetics of the hydrolysis and condensation reactions being different for each monomer, which generate different intermediates and eventual structures during the annealing process. The superior tunable luminescent performance of these environmentallyfriendly materials provides them with the potential for the fabrication of silicon-based light sources.
Synthesis of SiO 2 Nanoparticles by Sol-Gel Method and Their Optical and Structural Properties
Romanian Journal of Information Science and Technology, 2020
This paper focuses on the sol-gel synthesis of SiO2 nanoparticles for solar cells. The prepared samples were characterized by Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), fluorescence (FL) spectroscopy and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy studies revealed the presence of Si-O-Si stretching vibration bonding at 1093, 798 and 459 cm −1. SEM micrograph showed nearly irregular SiO2 nanoparticles. The calculated average particle diameter was 192 nm by DLS technique. The FL spectrum shows an emission band at 644.8 nm in the visible range and two broad excitation peaks at 359 and 718 nm. The optical and morphological properties of the as-prepared SiO2 nanoparticles are presented.
Synthesis and Luminescent Properties of Silicon Nanocrystals
Nanocrystals and Nanostructures, 2018
Nowadays, study of silicon-based visible light-emitting devices has increased due to large-scale microelectronic integration. Since then different physical and chemical processes have been performed to convert bulk silicon (Si) into a light-emitting material. From discovery of Photoluminescence (PL) in porous Silicon by Canham, a new field of research was opened in optical properties of the Si nanocrystals (Si-NCs) embedded in a dielectric matrix, such as SRO (silicon-rich oxide) and SRN (silicon-rich nitride). In this respect, SRO films obtained by sputtering technique have proved to be an option for light-emitting capacitors (LECs). For the synthesis of SRO films, growth parameters should be considered; Si-excess, growth temperature and annealing temperature. Such parameters affect generation of radiative defects, distribution of Si-NCs and luminescent properties. In this chapter, we report synthesis, structural and luminescent properties of SRO monolayers and SRO/SiO 2 multilayers (MLs) obtained by sputtering technique modifying Si-excess, thickness and thermal treatments.
Journal of Nanoparticle Research, 2008
The time changes of photoluminescence (PL) characteristics of porous silicon (porSi) powder during storing in different ambients have been reported. A porous silicon material with embedded Si nanocrystals of size of few nanometers was prepared by an electrochemical method from 10 to 20 Ωcm p-type Si wafers, and both constant and pulse current anodization regimes were used. A powder with a submicron average particle size was obtained by simple mechanical lift-off of the porous layer followed by additional manual milling. The air, hexane, and water as storage media were used, and modification by a nonionic surfactant (undecylenic acid) of the porSi surface was applied in the latter case. Dependence of PL characteristics on preparation and storage conditions was then studied. A remarkable blue shift of a position of PL maximum was observed in time for porSi powders in each storage media. In water suspension a many-fold build-up (10–30) of PL intensity in a time scale of few days was accompanied by an observed blue shift. Photoluminescence time behavior of porSi powders was described by a known mechanism of the change of porSi PL from free exciton emission of Si nanocrystals to luminescence of localized oxidized states on the Si nanocrystal surface.