SiO2 Host Matrix Research Articles

Nanoarhitectonics of Inorganic-Organic Silica-Benzil Composites: Synthesis, Nanocrystal Morphology and Micro-Raman Analysis.

The synthesis of nanosized organic benzil (C6H5CO)2 crystals within the mesoporous SiO2 host matrix was investigated via X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and ab initio lattice dynamics analysis. Combining these methods, we have proved that the main structural properties of benzil nanocrystals embedded into SiO2 host membranes with pore diameters of 6.0, 7.8, 9.4, and 13.0 nm are preserved compared to a bulk benzil crystal. Space confinement has an insignificant impact on the lattice vibrational properties of benzil crystals implanted into the host matrices. The ab initio lattice dynamics calculation of the phonon spectrum in the Brillouin zone center shows the mechanical and dynamical stability of benzil lattice, revealing very low optical frequency of 11 cm-1 at point Γ.

Ion-beam induced quasi-dynamic continual disorder in Bi-implanted Hongan silica glass

We have studied optical properties of glassy silicon dioxide (Hongan Silica Glass Store, China) irradiated with 30 keV bismuth ions. A broadening with a low-energy shift of absorption edge was found for the samples treated with 1 × 1016 – 3 × 1017 сm–2 ion fluences. The dose dependences of characteristic Urbach energy and width of the optical gap for direct interband transitions were determined and plotted. Based on the linear-type correlation between Urbach energy and optical gap width, the D/K ratio of deformation potential constants was established as well. The constancy of the D/K ratio for silicon dioxide at different fluences of bismuth ions indicates the proportionality between the values of the optical gap and band tails length, which are associated with the static atomic disorder of SiO2 host-matrix. An explanation of the obtained regularities was given using the quasi-dynamic (thermodynamic) approach. It was postulated that structural damage caused by ion-beam treatment determines Boltzmann entropy's magnitude as a combination of system various microstates. The functional dependence of σ-parameter (disordering effective cross-section) on the ion fluence has been established and proved experimentally.

Bi-doped silica glass: A combined XPS – DFT study of electronic structure and pleomorphic imperfections

The results of X-ray photoelectron spectroscopy analysis (core-levels, valence band) and first-principles modelling of bismuth implanted silicon dioxide electronic structure at various Bi-concentrations are reported. Most attention is paid to the study of Bi–O–Si chemical linkages and theoretically derived scenarios of Bi-embedding into SiO2 host-matrix. XPS analytics performed demonstrates the presence of spectral features related both with bismuth-bismuth and pleomorphicaly stretched bismuth-oxygen (Bi/O⋯Si–O) bonds fabrication at lowest employed pulsed-periodical Bi-ion fluence 5 × 1016 cm−2. The latter provides pleomorphic spectral separation of oxygen 2s band into O(I) 2s and O(II) 2s sub-bands. It was found that bismuth pairs of stoichiometric and nonstoichiometric (interstitial) impurities are responsible for that. Further increase in ion fluence up to 3 × 1017 cm−2 yields, in the main, the growth of α-Bi2O3-like frameworks within the volume of initial amorphous SiO2-host what have been interpreted as an appearance of stoichiometric Bi-impurity pairs. The results obtained well agree with our previous investigations of electronic structure of Bi-doped oxide host-matrices and theoretical MD-Tersoff third-party data. New approach toward modelling realistic process of ion-implantation was proposed and discussed.

Quasi-Dynamic Approach in Structural Disorder Analysis: An Ion-Beam-Irradiated Silica

Optical properties of glassy silicon dioxide irradiated with 30 keV rhenium ions were investigated. The blurring and low-energy shift of the sample absorption edge was established in 5 × 1015–5 × 1017 cm–2 range of ion fluences. Dose dependences of characteristic Urbach energy EU and optical gap width were obtained for direct interband transitions. The ratio of deformation potential constants D/K was determined on the basis of the linear correlation between EU and parameters. The constancy of D/K ratio at different ion fluences indicates proportionality between optical gap values and band tails caused by local displacements of atoms in SiO2 host matrix. An interpretation of established regularities was given in the framework of thermodynamic approach. The structural damages induced by ion irradiation as a set of various system microstates and relationship with Boltzmann entropy value were postulated. Thermodynamic temperature and ion fluence were considered as equivalent factors that determine a certain d...

Surface plasmon resonances in ellipsoidal bimetallic nanoparticles

The surface plasmon response of three-layered bimetallic nanoparticles embedded in a SiO2 host matrix is studied for different geometries. The analytical solution for the electromagnetic response in relation to the extinction cross section of the bimetallic nanoparticles is obtained by means of quasistatic theory. To show the extinction spectra of the three-layered bimetallic nanoparticles, we chose two different metals, namely, Ag and Au-Ag 50:50 alloy. The optical properties of the metals studied are described within the modified Drude-Sommerfeld model of the dielectric function with parameters accounting for the contribution of conduction electrons and interband transitions. We found that the position of the surface plasmon resonance depends on the dielectric function of the intermediate medium between the Au-Ag 50:50 alloy core and the Ag shell, the thickness of the Ag shell, the thickness of the intermediate medium, and the aspect ratio of the three-layered nanoparticles.

Elaboration and characterization of glass–ceramic enriched by heavily manganese doped zinc silicate nanoparticles for optoelectronic applications

Nanocrystallines Mn2+-doped zinc silicate (β-Zn2SiO4:Mn) embedded in SiO2 host matrix were synthesized in two steps. In the first one a sol–gel process was used for the elaboration of silica aerogel monolith enriched by ZnO:Mn nanoparticles using supercritical conditions of ethanol. In the second step a simple solid-phase reaction under natural atmosphere at 1500 °C was investigated. The structure and texture of the obtained nanocomposites were studied by X-ray diffraction and transmission electron microscopy respectively. The optical results indicate that the obtained nanocomposites have excellent luminescence properties in the visible range. In addition, the PL spectrum for the β-Zn2SiO4:Mn/SiO2 nanocomposite reveals a band centered at about 584 nm attributed to the 4T1–6A1 transitions of Mn2+ ions. The intensive yellow luminescence presents a red shift and the lifetime is relatively weak compared to the known luminescence properties of this material. The obtained results are attributed to the protocol used and the excess of Mn2+ ions. The linear diminishing behaviours of the PL integrate intensity with the operating temperature, and the variation of the time decay with the Mn2+ contents; make it possible to anticipate the utilization of this material in luminescence thermometry.

Plasmon coupled photoluminescence from silver coated silicon quantum dots

The surface plasmon enhanced photoluminescence (PL) emission of silver coated Si/SiO2 quantum dots (QDs) is investigated theoretically and numerically for different parameters of the QDs. Due to the interaction of radiation with the silver coat, a local surface plasmon oscillation is established which in turn results in a considerable resonant enhancement of the local field in the QDs. The local field enhancement factor inside of the silver coated spherical Si/SiO2 QDs is solved using the Laplace equation. Utilizing this enhancement factor, the plasmon enhanced radiative recombination rate, the spectral absorption, and the PL intensity of ensembles of silver coated Si/SiO2 QDs embedded in a SiO2 host matrix are studied. The induced electric field increases the overlapping of the electron and hole wave functions in the QDs leading to an increase in radiative recombination rate, spectral absorption, and the PL intensity. Moreover, by varying the thickness of silver coat and SiO2 spacer, the surface plasmon resonance frequency can be tuned to the longer wavelength regions in the visible spectrum. This enhances the coupling between surface plasmon resonance frequency of the silver coat and the energy gap of silicon QDs. It is found that the radiative recombination rate, spectral absorption and photoluminescence intensity increase up to 3 folds compared to the QDs without a metal coat.

Green and yellow luminescence properties of Willemite Zn2SiO4 nanocomposites by sol–gel method

Nanoparticles of willemite, α-Zn2SiO4 have been prepared by a sol–gel method. These samples were prepared by a simple solid-phase reaction under natural atmosphere at 1200 °C after the incorporation of ZnO:Mn and ZnO:V nanoparticles in silica monolith. The nanophosphors powder samples were characterized using X-ray diffraction, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. XRD analysis revealed that the α-Zn2SiO4 phase was at 1200 °C. In addition, the PL spectrum for the α-Zn2SiO4:Mn nanocomposite showed that a dominant peak at 525 nm which is due to4T1–6A1 transitions of Mn2+ ions. In the case of α-Zn2SiO4:V, the PL had shown a band centered around 540 nm. This band is due to the V in the interfaces between Zn2SiO4 particles and SiO2 host matrix. The findings of this work are very promising and can justify the use of these novel materials as a potential candidate in the field of photonic applications.

Photoluminescence and thermal stability of Tb3+-doped Gd2O3 nanoparticles embedded in SiO2 host matrix

Terbium doped SiO2-Gd2O3 materials were obtained by a sol-gel process and heat-treated at 1000 °C. The effect of Tb3+concentration on structural, optical and photoluminescent properties of materials are reported here. FT-IR indicated the presence of Gd2O3 and SiO2 in the composition of materials. XRD showed the formation of the Gd2O3 cubic phase without the presence of phase impurities, and lattice parameter calculations indicated the effective inclusion of Tb3+ in Gd2O3 crystalline structure. SEM analysis revealed spherical particles of Gd2O3 and TEM confirmed that these particles are included in the amorphous SiO2. Excitation spectra show bands in the UV-region at characteristic wavelengths of the Gd2O3 host absorption. Emission spectra were collected by changing the excitation, and the intensity shows dependence on the UV photon energy. Tb3+-doped Gd2O3 grown into SiO2 showed higher Tb3+ lifetimes which are ideal for photonic applications. The temperature significantly influenced the luminescence of the materials, with chromaticity changing from green to blue region. The activation energy for thermal quenching (Ea) was determined by an Arrhenius methodology and the material shows a high thermal stability (Ea for thermal quenching = 0.378 eV).

The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios

The following scenarios of Re-embedding into SiO2-host by pulsed Re-implantation were derived and discussed after XPS-and-DFT electronic structure qualification: (i) low Re-impurity concentration mode → the formation of combined substitutional and interstitial impurities with Re2O7-like atomic and electronic structures in the vicinity of oxygen vacancies; (ii) high Re-impurity concentration mode → the fabrication of interstitial Re-metal clusters with the accompanied formation of ReO2-like atomic structures and (iii) an intermediate transient mode with Re-impurity concentration increase, when the precursors of interstitial defect clusters are appeared and growing in the host-matrix structure occur. An amplification regime of Re-metal contribution majority to the final Valence Band structure was found as one of the sequences of intermediate transient mode. It was shown that most of the qualified and discussed modes were accompanied by the MRO (middle range ordering) distortions in the initial oxygen subnetwork of the a-SiO2 host-matrix because of the appeared mixed defect configurations.

Tunable optical properties of co-sputtered Ti-SiO_2 nanocomposite thin films

In this work, optical constants of direct current (DC) and radio frequency (RF) co-sputtered Ti-SiO2 nanocomposite thin films were investigated and tuned by controlling the deposition power of Ti in the SiO2 host matrix. X-ray photoelectron spectroscopy (XPS) results confirmed that the metallic Ti was completely oxidized into different titanium oxide states while the Si4+ state was reduced to the Si2+ or Si0 state by observing the Ti 2p, O 1s and Si 2p line shapes changing under different deposition conditions. The optical constants of the composites were characterized with a spectroscopic ellipsometer (SE) and reduced by using the modified harmonic oscillator approximation (HOA) model. The results show that the metal-dielectric nanocomposite will have an advantage over natural materials because its optical properties of n and k can be properly tuned by adjusting the concentration of Ti in the Ti-SiO2 nanocomposites, thus satisfying the requirements of photonic device design and applications in broad spectral regions.

Evaluation of Distributed OFDR-Based Sensing Performance in Mixed Neutron/Gamma Radiation Environments

We report the study of a radiation resistant single mode optical fiber doped with fluorine exposed to mixed neutron and $\gamma $ -radiation up to $10^{17}$ n/cm2 fluence and >2 MGy dose to evaluate its performances when used as the sensing element of a distributed Optical Frequency Domain Reflectometry (OFDR). The use of complementary spectroscopic techniques highlights some differences between the responses of solely $\gamma $ -radiation (10 MGy) or mixed neutron and $\gamma $ ( $10^{17}$ n/cm $^{2}+>2$ MGy) irradiated samples. Those differences are linked to the defect generation rather than to structural changes of the ${a}$ -SiO2 host matrix. We show that a modification of the refractive index of $\sim 10^{\mathrm {-5}}$ is induced at the highest investigated neutron fluence. However, the feasibility of distributed temperature measurements along the irradiated fiber is demonstrated with an accuracy of 0.1 °C over a sensing length up to ~ 130 m with the tested OBR4600 interrogator. These results are very promising for the integration of OFDR sensors in mixed neutron and gamma radiation environments.

Effect of annealing temperature on the luminescence properties of Zn2SiO4:V nanocomposite

Yellow and green lights emitting vanadium doped Zn2SiO4 particles embedded in a SiO2 host matrix were synthesised by a sol–gel method. After the incorporation of ZnO:V nanoparticles in a silica monolith using a sol–gel method with supercritical drying of ethyl alcohol in two steps, it is heat treated in air at 1200°C and 1500°C for 2h in order to obtain the α and β phases of Zn2SiO4 nanocomposites. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the phase purity, particle size and morphology. In addition, photoluminescence (PL) is used for optical studies. The PL shows a band centred at about 540nm in the case of α-Zn2SiO4. In the case of β-Zn2SiO4, the PL reveals a band centred at about 526nm. It is suggested that radiative defects attributed to the vanadium in the interfaces between the Zn2SiO4 particles and the SiO2 host matrix resulting from heat treatment, were responsible for theses luminescence bands.

Photoconversion from yellow-to-green in vanadium doped zinc silicate nanophosphor material

We report a novel synthesis process of V doped β-Zn2SiO4 green nanophosphors based on sol–gel method. After the incorporation of ZnO:V nanoparticles in a silica monolith using a sol–gel method with supercritical drying of ethyl alcohol in two steps, it is heated in air at 1500°C for 2h. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the phase purity, particle size and morphology. In addition, photoluminescence (PL) is used for optical studies. XRD results indicate that pure phase of β-Zn2SiO4 with triclinic structure was obtained after thermal treatment at 1500°C. The PL shows an new intensive luminescence band in the visible range centered at about 526nm, attributed to vanadium in the interfaces between the Zn2SiO4 nanoparticles and the SiO2 host matrix.

Synthesis by sol–gel process, structural and luminescence of V and Mn doped α-Zn2SiO4

A two-step sol–gel process is used for the preparation of undoped, Mn and V-doped Zn2SiO4 nanoparticles embedded in silica host matrix. The formation of a crystalline phase of willemite structure in the samples was confirmed by XRD measurements. Undoped Zn2SiO4 sample exhibits an intense emission band centered at 760 nm, can be attributed to the formation of non-bridging oxygen hole centers (NBOHcs) excited at the spectral region hν ≥ 5.4 eV. In the case of Zn2SiO4:V, a band centered at 540 nm has been detected. This emission is allocated to the V in the interfaces between Zn2SiO4 particles and SiO2 host matrix. In addition, the green emission peak centered around 525 nm of Zn2SiO4:Mn nanoparticles is attributed to the 4T1–6A1 transitions of Mn2+ ions. The crystallinity and luminescent property of nanoparticles were investigated.

Sol–gel synthesis, structural and luminescence properties of MT-doped SiO2/Zn2SiO4 nanocomposites

The sol–gel method is used for the preparation of undoped, Mn and V-doped Zn2SiO4 particles embedded in SiO2 host matrix. The phase purity and morphological features were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations. The obtained SiO2/Zn2SiO4 nanocomposite, exhibits a strong photoluminescence (PL) band centered at around 760nm, attributed to energy transfer occurs from Zn2SiO4 particles to NBOHs interfaces defects. In addition, the PL spectrum for the SiO2/Zn2SiO4:Mn nanocomposite showed that a dominant peak at 525nm appeared, which originated from the 4T1–6A1 transitions of Mn2+ ions. In the case of SiO2/Zn2SiO4:V, the PL reveals a band centered at about 540nm attributed to the effect of the V5+ in the host matrix nanocomposite.

Sol–gel synthesis and luminescence of undoped and Mn-doped zinc orthosilicate phosphor nanocomposites

Zn2SiO4 and Zn2SiO4:Mn particles embedded in SiO2 host matrix prepared by sol gel method under supercritical conditions of ethyl alcohol in two steps. Were prepared by a simple solid-phase reaction under natural atmosphere at 1200°C after the incorporation of ZnO and ZnO:Mn nanoparticles, respectively, in silica monolith. In the case of SiO2/Zn2SiO4 nanocomposite, the powder with an average particle size of 80nm shows a strong luminescence band centred at around 760nm in the visible range. In addition, the PL spectrum for the SiO2/Zn2SiO4:Mn nanocomposite showed that a dominant peak at 525nm appeared, which originated from the 4T1–6A1 transitions of Mn2+ ions. The luminescence properties of nanocomposites were characterized by emission and excitation spectra as well their dependencies of upon temperature and power excitation density.

Luminescence properties of green emission of SiO2/Zn2SiO4:Mn nanocomposite prepared by sol–gel method

Green light emitting Mn2+ doped Zn2SiO4 particles embedded in SiO2 host matrix were synthesized by a sol–gel method. After the incorporation of ZnO:Mn nanoparticles in a silica monolith using sol–gel method with supercritical drying of ethyl alcohol in two steps, it was heat treated in air at 1200°C for 2h in order to obtain the SiO2/α-Zn2SiO4:Mn nanocomposites. The microstructure of phosphor crystals was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD results indicate that the pure phase α-Zn2SiO4 with rhombohedral structure was obtained after thermal treatment at 1200°C. The SiO2/α-Zn2SiO4:Mn nanocomposites with a Mn doping concentration of 1.5at% exhibit two broadband emissions in the visible range: a strong green emission at around 525nm and a second one in the range between 560 and 608nm. This nanocomposite with a Mn doping concentration of 0.05 shows the highest relative emission intensity. Upon 255nm excitation, the luminescence decay time of the green emission of Zn2SiO4:Mn around 525nm is 11ms. The luminescence spectra at 525nm (4T1–6A1) and lifetime of the excited state of Mn2+ ions-doped Zn2SiO4 nanocrystals are investigated.

Synthesis and luminescence of SiO2/Zn2SiO4 and SiO2/Zn2SiO4:Mn composite with sol-gel methods

The sol gel method is used for the preparation of undoped and manganese-doped Zn2SiO4 particles embedded in SiO2 host matrix with supercritical drying of ethyl alcohol in two steps. Zn2SiO4 and Zn2SiO4: Mn were prepared by simple solid-phase reaction in a natural atmosphere at 1200°C after the incorporation of the nanoparticles of ZnO and ZnO: Mn, respectively, in the silica monolith. The photoluminescence (PL) measurements show a band centered at about 760nm in the case of non-doped Zn2SiO4 which is attributed to energy transfer from Zn2SiO4 particles to NBOHs interface defects. In the case of Manganese doped Zn2SiO4, the PL reveals a band centered at about 525nm attributed to Mn2+ in Zn2SiO4. Photoluminescence excitation (PLE) measurements show different origins of the emission. It was suggested that electronic transition 4T1(4G)→6A1(6S) associated with Mn2+ ions in willemite and the presence of Mn2+ in intensive crystal field were responsible for these luminescence band centered at 525nm.

Photoluminescence study of ZnO–SiO2 nanostructures grown in silica matrix obtained via sol–gel method

ZnO–SiO2 nanocomposite consisting of ZnO nanostructures grown in SiO2 (silica) host matrix was obtained via hydrolysing Tetraethylorthosilicate (TEOS) with ethanolic solution of Zinc nitrate hexahydrate using Sol–gel method. Systematic study of the key parameters (precursor, concentration, and heat treatment conditions) has been taken into account that influences the growth mechanism and morphology of the as formed nanostructures. X-ray diffraction (XRD) analysis was used to determine the crystallinity, particle size and lattice parameter. Scanning electron microscopy (SEM) of the sample reveals the formation of ZnO nanostructures in silica matrix. Room temperature Photoluminescence (PL) measurement of the sample was done to understand the nature of possible defect level transition responsible for visible and rarely observed orange–red emissions in ZnO. This study reveals the usefulness of the nanocomposites as a luminescent material.