Search results for "luminescence."

Defect-related visible luminescence of silica nanoparticles

2013

The high photon emissivity in the visible spectral range is one of the most relevant phenomena emerging from the reduction of silica down to nanoscale; hence it is promising for the development of optical nanotechnologies (down converter, probes, display). It is well accepted that the origin of this luminescence is related to the high specific surface (~100 m2/g) that favors the formation of optically active defects at the nanosilica surface. With the aim to clarify the role of specific luminescent defects, here we report a detailed study of spectral and decay features by time-resolved photoluminescence spectra under a visible-UV tunable laser excitation. Our study is carried out on differe…

Vibrational properties of the surface-nonbridging oxygen in silica nanoparticles

2008

By studying the site-selective luminescence spectra of oxidized silica nanoparticles we identify the electronic and the vibrational lines associated with the surface nonbridging oxygen, $\ensuremath{\equiv}{\text{Si-O}}^{\ifmmode\bullet\else\textbullet\fi{}}$. This defect emits a zero-phonon line inhomogeneously distributed around 2.0 eV with full width at half maximum of 0.04 eV, weakly coupled with the local ${\text{Si-O}}^{\ifmmode\bullet\else\textbullet\fi{}}$ stretching mode whose frequency is measured to be $920\text{ }{\text{cm}}^{\ensuremath{-}1}$. These findings are different from those of the well-characterized defect in the bulk silica thus evidencing structural peculiarities of …

Time Resolved Photoluminescence Associated with Non Bridging Oxygen Hole Centers in Irradiated Silica

2007

Luminescence activity of irradiated SiO2-clathrate Melanophlogite

2013

Self-limiting and complete oxidation of silicon nanostructures produced by laser ablation in water

2016

Oxidized Silicon nanomaterials produced by 1064 nm pulsed laser ablation in deionized water are investigated. High-resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy allows to characterize the structural and chemical properties at a sub-nanometric scale. This analysis clarifies that laser ablation induces both self-limiting and complete oxidation processes which produce polycrystalline Si surrounded by a layer of SiO2 and amorphous fully oxidized SiO2, respectively. These nanostructures exhibit a composite luminescence spectrum which is investigated by time-resolved spectroscopy with a tunable laser excitation. The origin of the observed luminescen…

Luminescence of ODC(II) in quartz and cristobalite glasses

2022

Abstract The results of the optical spectroscopy of twofold coordinated silicon centers – ODC(II) in quartz and cristobalite glasses are presented. The luminescence and excitation spectra attributed to different local symmetry of ODC(II) were investigated under synchrotron excitation in the VUV region. The observed differences in the luminescence and excitation spectra of ODC(II) are caused by the environment and, therefore, short-range order in the samples.

Thermostimulated luminescence and electron spin resonance in X-ray- and photon-irradiated oxygen-deficient silica

2007

Abstract Influences of oxygen-deficiency on radiation properties of high-purity, low-OH fused silica were studied. It is found that thermostimulated luminescence (TSL) peaks are different for photo (7.7 eV) and X-ray excitation at 77 K. X-ray excitation produces TSL peaks at 125 and 170 K corresponding to the anneal temperatures of two types of self-trapped holes centers STH2 and STH1, respectively, detected by electron spin resonance (ESR). Oxygen-deficiency apparently increases the number of electron traps, stabilizing a larger number of STHs in the continuous defect-free silica network than is observed in similarly X-irradiated stoichiometric silica glasses. Photoexcitation of oxygen-def…

Investigation of optical and radiation properties of oxygen deficient silica glasses

1999

The deficiency of oxygen in pure silica manifests an absorption band at 5 eV as well as an absorption band of higher intensity at 7.6 eV. The band at 5 eV is associated with lone twofold-coordinated silicon centers. The nature of the main band at 7.6 eV has been studied using silica samples with different levels of oxygen deficiency. The excitation via the 7.6 eV band produces a photoelectric response as well as inner center and recombination type luminescence. Two main luminescence bands of the twofold-coordinated silicon center appear: a blue band (2.7 eV) and a UV band (4.4 eV). Induced absorption with several bands as well as thermally stimulated luminescence with complex peak structure…

Structural and in situ vibrational study of luminescent cluster assembled silicon thin films

2006

A Low Energy Cluster Beam Deposition apparatus is employed to produce cluster assembled silicon thin films (1-500 nm thick) by using a laser vaporization source. The generated clusters are studied since their formation through time of flight mass spectra and the calculated size in the gas phase are compared with those of the deposited aggregates obtained through Dynamic Scanning Force Microscopy. The deposited material is also studied "in situ" by Raman and infrared spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. A comparison of the film properties before and after their air exposure shows that the exposition induces a consis…

Gold coated porous silicon nanocomposite as a substrate for photoluminescence-based immunosensor suitable for the determination of Aflatoxin B1.

2017

Abstract A rapid and low cost photoluminescence (PL) immunosensor for the determination of low concentrations of Aflatoxin B1 (AFB1) has been developed. This immunosensor was based on porous silicon (PSi) covered by thin gold layer (Au) and modified by antibodies against AFB1 (anti-AFB1). PSi layer was formed on silicon substrate, then the surface of PSi was covered by 30 nm layer of gold (PSi/Au) using electrochemical and chemical deposition methods and in such ways PSi/Au (El.) and PSi/Au (Chem.) structures were formed, respectively. In order to find PSi/Au the most efficiently suitable for PL-based sensor design, structure several different PSi/Au (El.) and PSi/Au (Chem.) structures were…