Non-bridging Oxygen Hole Centers Research Articles

Optical spectra in pure-silica-core single mode optical fibers after high-fluence reactor irradiation

The paper describes the study of radiation-induced attenuation (RIA) spectra in reactor-irradiated single mode optical fibers (OFs) with differente high-temperature coatings (polyimyde, aluminum and copper). The OFs were previously irradiated up to fast neutron fluence 1.8·1020 n/cm2 and gamma dose 2.32 GGy. After three years of annealing at room temperature (RT), the RIA spectra were examined within the range of 650–1700 nm. All RIA mechanisms acting within this spectral range were identified: absorption bands attributed to non-bridging oxygen hole centers, a long-wavelength (LW) band with a maximum at λ > 1800 nm, and unsaturated “grey” loss due to coating microbendings or damage. It was found out that RIA asocciated with the LW band can be significantly annealed at room temperature in polyimide-coated OFs. RIA mechanisms influenced by the coating were found to be more stable than those causing LW-RIA.The LW-RIA arising during reactor and gamma irradiation exhibits a similar shape, approximated by the Kubo-Greenwood formula for alternative conductivity, which describes the absorption of self-trapped holes (STH) and exibits close thermal stability at RT. This suggests a STH-like nature of LW-RIA. The accurate approximation of the RIA spectrum in the near-infrared range requires considering contributions of the unsaturated loss or contributions of an absorption band peaking at an energy of 1.33 eV with a half-width of 0.45 eV.

Copper nanoparticle and point defect formation in Cu+-Na+ ion-exchanged glass using protons of 2 MeV energy.

There are several applications for irradiating materials with protons that could provide alternative methodologies to synthesize and induce the formation of new compounds of different size scales. In this study, we explored the effects of proton irradiation oncommercial glass silicate that was previously subjected to a Cu+-Na+ ion exchange (IE) treatment at 600 °C for a duration of 60 min. The ion-exchanged glass samples were irradiated with protons (p+) of 2 MeV energy at doses in the range of thousands of grays (3.3 × 103, 7.9 × 103 Gy) and hundreds of thousands of grays (3.6 × 105 Gy). Significant changes in the optical and structural properties were observed post the radiation treatment. The UV-Visible absorption spectra of the irradiated samples revealed the appearance of overlapping absorption bands, which could be deconvoluted into three Gaussian-shaped bands peaking at 566, 620 and 680 nm. These three bands could be attributed to the surface plasmon resonance (SPR) of copper nanoparticles, non-bridging oxygen hole centers (NBOHCs) and self-trapped hole (STH) defects, respectively. Prominent photoluminescence (PL) was observed in the Cu-exchanged and irradiated samples, mainly induced by the presence of both Cu+ and Cu2O. Increasing the irradiation dose led to an increase in the PL intensity due to the conversion of Cu2+ ions into Cu+. This result was confirmed by electron paramagnetic resonance (EPR) spectroscopy that shows a decrease in the Cu2+ signal when increasing the dose of proton exposure. Transmission electron microscopy (TEM) and high-resolution TEM (TEM and HRTEM) observations confirmed the presence of copper nanoparticles (CuNPs) in the doped and p+ irradiated Cu-exchanged glass silicate samples. These CuNPs were found to be crystalline with an average size of 12.39 nm.

Evolution of point defects in mechanical cracks of fused silica after CO2 laser melting

The traditional polishing method inevitably results in subsurface cracks in the fused silica, which seriously degrades their ultraviolet laser damage resistance. CO2 laser irradiation can melt these cracks and improve their laser induced damage threshold (LIDT). Photoluminescence spectrum and SEM-FIB were employed to investigate the changes in the material microstructure at the crack location with CO2 laser melting. The density of the oxygen-deficient centers of type II (ODC II) defects decreases, while the density of the non-bridging oxygen hole center (NBOHC) defects increases after high-temperature melting. The reason for this change is related to the dihydroxylation reaction and the participation of environmental oxygen in the defect type conversion. The reduction of ODC II defects is most likely the reason for the improvement of LIDT.

Controlling photoluminescence of silicon quantum dots using pristine-nanostates formation

This study investigates the effective control of photoluminescence (PL) of silicon nanocrystals (Si–NCs) embedded in a SiO2 matrix, with a specific focus on tuning the luminescent wavelength profile and intensity for silicon-based optoelectronic applications. By manipulating the composition ratio (x) of SiOx, the well-known simultaneous changes in PL peak position and intensity were observed after annealing. To preserve the desired wavelength characteristics and enhance the luminesce intensity, we propose a novel approach to generate pristine nanostates (PNs) for Si-NC formation using proton irradiation (PI). The application of proton irradiation was found to be successful in significantly increasing PL intensity while strongly suppressing the peak position shifts. Through extensive spectroscopic analysis including PL, X-ray photoelectron spectroscopy, and absorption spectroscopy, we investigate specific defect states in the SiOx matrix, and identified as PNs. We interpret that these PNs consist of self-trapped exciton, E′ center, non-bridging oxygen hole center, and oxygen-deficiency center states. In the as-grown sample, the PNs promote appropriate phase separation and play a significant role in stabilizing the structure during the subsequent annealing processes. This study elucidates the Si-NC formation mechanism by enhancing O-diffusion-induced phase separation, a process accelerated in SiOx with controlled PNs. The proposed PI-induced PNs offer a novel pathway for developing Si-based optoelectronic devices with desired characteristics in the operating wavelength range. These findings open up promising possibilities for advanced silicon-based optoelectronic applications.

Effects of oxygen loading on the red-luminescence of non-bridging oxygen hole centers in γ-irradiated silica glasses

Ultra-high purity Corning 7980 and Corning 7979 silica glasses, respectively with high and low contents of hydroxyl and hydrogen, were specifically selected to investigate the effects of O2 loading on the 1.9 eV red luminescence of the gamma-ray induced non-bridging oxygen hole center (NBOHC), whose luminescence intensity is beneficial not only to predict the laser damage of silica but also to the targeted improvements in the preparation-treatment processes of silica. The UV trasmittance spectra, the UV excitation spectra, the visible emission spectra and the red emission lifetime decay curves were determined for these two types of the gamma-ray irradiated silica glasses before and after O2 loading. The content ratios of Si dangling bond (Si-E′) to NBOHC in silica glasses before and after O2 loading are estimated. The formation precursors and other related defects for NBOHC, such as Si-E′, Si-O-Si bond, Si-O-H bond, peroxy radical and linkage, oxygen-deficient centers ODC(I) and ODC(II), etc, are discussed. The bandwidths of the excitation and emission spectra before and after O2 loading are compared at the lower energy side of the spectra. The average emission lifetimes and especially the decay curves of the red luminescence before and after O2 loading are analyzed. There appear two types of NBOHCs with and without neighbouring hydrogen interaction at room temperature, respectively corresponding to the shorter and longer lifetime components. After O2 loading, the shorter lifetime component disappears and becomes the longer one, indicating that the hydrogen-bonded NBOHC is altered into the non-bonded. It is suggested that the analysis of the shorter and longer lifetime components of the red luminescence can be utilized in the laser damage prediction as well as the preparation and treatment processes of silica.

Analysis of red-luminescence lifetime components of non-bridging oxygen hole centers in γ-ray irradiated silica glasses

The relation between 1.9 eV red-luminescence intensity of non-bridging oxygen hole centers (NBOHCs) in silica and incident laser shot number was proved to be important to predict the occurrence of laser damage, in which a more precise prediction will benefit from a deeply understanding of the red-luminescence of NBOHCs. This study focuses on analyzing NBOHCs in silica glasses irradiated by gamma rays, including the electron paramagnetic resonance spectra in the main g2 factor range, excitation spectra in the UV range, emission spectra and emission lifetimes in the red range, as well as their relations with hydroxyl and temperature. At 53 K, the main g2-factor of NBOHCs in high-hydroxyl (high-OH) and low-hydroxyl (low-OH) silica differs by only ∼1.5 × 10−4. Whereas in the higher g-value side of the main g2-factor band, low-OH silica exhibited a little broadened resonance absorption bandwidth. At room temperature, the 5.64-3.44 eV excitation spectra monitoring at 1.9 eV and the 2.16-1.65 eV emission spectra exciting at 4.8 eV exhibit the same excitation peak of 4.54 eV and emission peak of 1.907 eV for both high-OH and low-OH silica. Whereas at liquid-N2 temperature, high-OH silica exhibits a broader emission bandwidth in the higher energy side of the red-luminescence band. At room temperature, the average emission lifetime of NBOHC in high-OH silica is 14.5 µs, whereas that in low-OH silica is 13.4 µs. However, at liquid-N2 temperature, their average lifetimes respectively increased and decreased greatly to 22.3 and 9.7 µs, showing a quite obvious variation. In high-OH silica, the large number of hydroxyl attract the hydrogen ions that are released with the temperature decrease, forming metastable hydrogen-bonded hydroxyl. Finally, only NBOHCs corresponding to longer lifetime components, without neighboring hydrogen and its interaction, remain in the high-OH silica at lower temperature. In low-OH silica, there is few hydroxyl, so that the hydrogen released with the temperature decrease can only act on NBOHCs without neighboring hydrogen. Finally, those NBOHCs that correspond to shorter lifetime components and interact with neighboring hydrogen remain in the low-OH silica at lower temperature. The results on the characteristics of this red luminescence provides new ideas and ways for the future prediction about the laser damage of silica. Especially, the component analysis on the emission lifetime decay curves that can reflect the characteristics of NBOHCs and their neighboring environment can not only be used to distinguish between contributions to the red-luminescence from different types of NBOHCs, but also to analyze the relations between other ions or defects around NBOHCs and laser damage initiation, for a more precise prediction.

Evaluation of the sterilization effect on biphasic scaffold based on bioactive glass and polymer honeycomb membrane

AbstractThe sterilization is a core preoccupation when it comes to implantable biomaterials. The most common in industry is the gamma sterilization; however, the radiation used in this method can induce modifications in the material properties. This study investigates the impact of such radiations on the physicochemical properties and biological toxicity of a new biomaterial based on a poly‐l‐co‐d,l‐lactide polymer honeycomb membrane and bioactive glass (BG), combined, to form an assembly (membrane/BG assembly). The investigated BGs are the S53P4, which is FDA approved and clinically used, and 13‐93B20, a BG containing boron promising for bone regeneration. Infrared and photoluminescence measurements revealed that, upon irradiation, defects are created in the BGs molecular matrix. Defects were identified to be mainly non‐bridging oxygen hole center and occur in higher proportion in the 13‐93B20 making it more sensitive to irradiation compared to the S53P4. However, the irradiation does not significantly impact the structure of the BGs. On the membrane side, the molecular weight is divided by two resulting in a lower shear stress resistance. However, the membrane honeycomb topography does not seem to be impacted by the irradiation. In contact with cells, no toxicity effect was observed, and BGs keep their bioactive properties by releasing ions beneficial to the cell fate and with no influence on apatite precipitation speed. Overall, this study showed that, despite some impact on the physicochemical properties, the irradiation does not induce deleterious effect on the membrane/BG assemblies and is therefore a suitable method for the sterilization of this novel biomaterial.

Radiation effects of B depletion and the generation of point defects in ternary borosilicate glasses by gamma rays

Borosilicate glass is one of the base materials which can solidify high-level radioactive waste. Therefore, its resistance to radiation attracted extensive attention. The borosilicate glass samples with different compositions were irradiated with gamma rays at ambient temperature. The interaction between the gamma rays and the glass network was discussed. The radiation effects were analyzed with nano-indentation, photoluminescence, Raman, Infrared, Ultraviolet and visible absorption, and X-ray photoelectron spectroscopies. The results indicate point defects such as non-bridging oxygen hole center (NBOHC) and peroxy radical were produced in glasses after irradiation. The depletions of sodium and boron in the surface of glasses were identified, which led to a decrease in hardness. The Urbach energies increased with the absorbed dose. A new analyzing method, the noise of Raman spectrum, was deduced to analyze the glass disorder. The noise and Urbach energy depended on the concentration of NBOHC, which is led by gamma radiation.

Defect generation mechanisms in silica under intense electronic excitation by ion beams below 100 K: Interplay between radiative emissions

Ion-beam effects on bulk silica at low temperature have been studied with the aim of understanding the routes and mechanisms leading from the initial generation of free carriers and self-trapped excitons (STEs) to the production of two stable defect structures in irradiated silica, non-bridging oxygen hole centers (NBOHCs) and oxygen deficient centers (ODCs). Ion beam induced luminescence (ionoluminescence, IL) spectra were obtained using 3 MeV H, 3.5 MeV He, 19 MeV Si, and 19 MeV Cl ions and a range of cryogenic irradiation temperatures from 30 to 100 K. The kinetic behavior of three emission bands centered at 1.9 eV (assigned to NBOHCs), 2.1 eV (assigned to the intrinsic decay of STEs), and 2.7 eV (assigned to ODCs) reveal the physical origin of these emissions under intense electronic excitation. The creation of NBOHCs is governed by a purely electronic mechanism. The kinetics curve of the NBOHC band shows two main contributions: an instantaneous (beam-on) contribution, followed by a slower fluence- and temperature-dependent process correlated with the concentration of STEs. The beam-on contribution is proportional to deposited ionization energy. The growth of the ODC band is linear in fluence up to around 2 × 1012 cm−2. The growth rate is independent of temperature but proportional to the number of radiation-induced oxygen vacancies per ion, showing, unambiguously, that the 2.7 eV emission can be associated with ODCs created in an excited state.

Theoretical studies on intrinsic electron traps in strained amorphous silica

Charge trapping in amorphous silica (a-SiO2) dielectric layer can degrade electrical performances of semiconductor devices. Earlier studies demonstrate that a SiO4 tetrahedra unit with a wide O-Si-O angle (≥132.0∘) can act as an electron trapping site in unstrained a-SiO2 cells. With first-principle calculations, in conjunction with molecular dynamic calculations, this work investigates the impacts of uniaxial tensile strain on one-electron trapping behaviors of a-SiO2, including atomic configurations and electronic properties. Stable states of strained a-SiO2 cells with an extra electron indicate that a SiO4 with a wide O-Si-O angle (≥132.0∘) and a long Si-O bond (≥1.660Å) making up the angle can act as a novel intrinsic electron tap. An electron trapping on this trap can generate a stable defect complex with two components: a negatively charged non-bridging oxygen hole center and a neutral oxygen vacancy with an unpaired electron.

Defect characteristic of oxygen-deficient Ge-doped preform using photoluminescence spectroscopy

Study has been made of the Photoluminescence properties of Ge-doped silica preforms fabricated using the MCVD process and subsequently subjected to γ-ray irradiation. The photoluminescence emissions pointed to the presence of defects related to oxygen vacancies. Two types of preform were fabricated, obtained using a different flow rate and deposition temperature for each case. Results from the absorption spectra of the samples named as P1 and P2, show a signature absorption peak at 5.1 eV and 6.8 eV, indicative of oxygen-deficient and oxygen-rich defects respectively. Photoluminescence investigation have been carried out before and after the irradiation process with both samples reveal two main peaks at 1.5 eV. The highest intensity at 1.5 eV is known as an interaction between the Non- Bridging Oxygen Hole Centre (NBHOC) with the presence of impurity in the glass matrix. Upon irradiation, weak peak can be observed at 1.8 eV, sample P1 and P2, the PL intensity increases by a factor of 20 × and 50 × , respectively. This peak is associated with the oxygen deficient state in the sample. The peak referring to defect known as Germanium Lone Pair Centre (GLPC) are observed in both samples, peak shown at 3.1 eV, regardless of the Germanium Oxygen Deficient Centre (GODC) content. In regard to this, it can be concluded that this defect is generated independently in all germanium samples and are not correlated with the GODC band observed in the absorption band.

Influence of spin–orbit coupling on the gamma-ray induced attenuation in high-OH silica fibers

There is an ever-increasing demand for radiation-tolerant optical systems in space and nuclear applications. This motivates leveraging advanced modeling techniques for the rational design of radiation-hard, application-specific optical materials. Here we used molecular dynamics, density functional theory, and solution of Maxwell’s equations to understand the role of point-defects on the radiation-induced attenuation in wet fused silica (a-SiO2:OH). We apply this approach to study γ-irradiated optical fibers, and find theoretical evidence that non-bridging oxygen-hole centers (NBOHC) are the primary microscopic defect responsible for radiation-induced attenuation in the visible-range. The nature of the defect states and implications for fiber efficiency are discussed. Spin–orbit coupling is found to play an important role in defining the optical properties of gamma-ray induced defects.

Proton irradiation induced damage effects in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>-based perovskite solar cells

Perovskite solar cells (PSCs) have a great potential for space applications due to their high specific power, low cost and high defect tolerance. PSCs used in space will be subjected to high-energy particle irradiation, especially proton irradiation, resulting in the decline of photovoltaic (PV) performance. However, the research on proton irradiation effects in PSCs is still in its infancy stage. In this work, the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) thin films and their PSCs are irradiated by protons with energy of 0.1, 2, 10, 20 MeV, etc. Irradiation-induced changes in PV parameters of the PSCs are studied as a function of proton fluence. The structural and surface morphological changes of the irradiated MAPbI<sub>3</sub> films and Au electrode layers of PSCs are characterized by X-ray diffraction and scanning electron microscopy. In addition, UV spectrophotometer is also employed to analyze the transmission loss in glass substrate induced by proton irradiation. It is found that PSCs exhibit superior resistance against proton irradiation. The PV properties of the PSCs don’t degrade after 0.1 MeV (2 MeV) proton irradiation up to a fluence of 1×10<sup>13</sup> p/cm<sup>2</sup> (1×10<sup>14</sup> p/cm<sup>2</sup>). The irradiation-induced damage in the charge transport layers may be the main cause for the performance degradation of PSCs. The gaseous products (NH<sub>3</sub> and CH<sub>3</sub>I) of perovskite decomposition eventually lead to exfoliation of the top Au electrode from the PSCs. Regarding 10 and 20 MeV proton irradiation with larger projected ion ranges, the irradiations create color center defects in glass substrate of PSCs, which results in a decrease in light transmission of visible spectrum. However, the color center defects, specifically non-bridging oxygen hole centers, will be partly annealed at room temperature or 100 ℃, reducing the transmission loss in glass. The reported results may help predict the performance degradation of PSCs in space irradiation environment.

Radiation responses of ultra-low loss pure-silica-core optical fibers in the visible to infrared domains

–We investigated the origins of the steady state X-ray radiation-induced attenuation (RIA) in the visible to infrared spectral domains of an ultra-low loss Telecom-grade single-mode optical fiber. This pure-silica core optical fiber presents very high RIA in this spectral range, larger than so-called radiation sensitive optical fibers. The RIA is mainly caused by the appearance of two broad absorption features around 600 nm and 1200 nm, both leading to RIA levels of ∼2 dB/m at 2 kGy(SiO2) at room temperature. While the infrared-RIA may be attributed to the absorption bands at 0.93 eV and 1.2 eV of possible variants of Self-Trapped Holes, the exact nature of the large 600 nm absorption around remains unclear. It could not be only related to a very efficient generation of Non-Bridging Oxygen Hole Centers but our analysis suggests the presence of another defect structure associated with an absorption band around 2.14 eV (FWHM = 0.52 eV), stable at room temperature, but that can be passivated by post irradiation hydrogen-loading treatment.

First principle studies on properties of silicon-vacancy related defects in amorphous silica

The non-bridging oxygen hole center (NBOHC) can decrease the transmission efficiency of the amorphous silica (α-SiO2) material. In radiation environments, the NBOHC can be produced by both the electronic (Se) and the nuclear (Sn) energy loss processes of the radiations. The Se-related formation channels of NBOHC have been well characterized. The Sn can produce isolated silicon vacancies within α-SiO2 by knocking out silicon atoms. With first principle calculations, this work investigates the characteristics of the silicon-vacancy defective α-SiO2 cells, including atomic configuration, electronic density of state and optical absorption coefficient. The stable states of the silicon vacancy defects suggest a direct and an indirect Sn-related formation channels for NBOHC. The silicon vacancy has two stable configurations, i.e., the case I contains two NBOHC along with a peroxy linkage (POL), and the case II has two POL. Thereafter, the Se can promote the transition from POL to NBOHC.

The influence of CeF3 on radiation hardness and luminescence properties of Gd2O3–B2O3 glass scintillator

The effect of CeF3 concentration and γ-irradiation on the physical, optical and luminescence properties of Gd2O3–B2O3–CeF3 glasses were studied in this work. Before irradiation, the addition of CeF3 in glass degraded the network connectivity observed from FTIR and possibly created the non-bridging oxygen (NBO) in glass structure. This NBO caused the reduction of Ce3+/Ce4+ ratio in XANES, the red-shift in transmission spectra and the raise of refractive index with addition of CeF3 content. Such red-shift also was influenced by 4f–5d transition of Ce3+ dopant. This ion generated the strongest photoluminescence (PL) and radioluminescence (RL) in 0.3 mol% CeF3-doped glass with nanoseconds decay time. The irradiation with γ-rays damaged the glass structure, broke the chemical bonds, and created color center in the glass network. The non-bridging oxygen hole center (NBOHC), that absorbed photons in the visible light region, caused the darkening, color change and increment of refractive index. These irradiation effects on glass were mitigated by the addition of CeF3 that the electron donation of Ce3+ decreased the number of NBOHC. The Ce3+/Ce4+ ratio in most glasses after irradiation then reduced compared to them before irradiation, resulting to the decrease in PL and RL intensity. Our results confirm that CeF3 can enhance the radiation hardness of glass and the 0.3 mol% CeF3-doped glass is a promising glass scintillator.

Impact effect of gamma irradiation on the optical, FTIR, ESR spectral properties and thermal behavior of some mixed (PbO + Bi2O3) borate glasses searching for shielding effects

Four borate glasses with mixed and equal heavy metal oxides PbO+Bi2O3 ranging from 70→55% were prepared by routine melting and annealing technique. These glasses were selected to identify the effects of gamma irradiation on glasses combining two heavy metal oxides (PbO, and Bi2O3) which are known to be of shielding nature towards irradiation. Collective measurements of the optical, structural FTIR and ESR. spectral properties of the prepared equal mixed glasses were carried out before and after a relatively high dose of gamma rays (6 M rad). Optical spectra of the glasses reveal before irradiation strong UV absorption due to trace ferric ions present as impurities in the chemicals used for the preparation of the glasses. After irradiation, an extra small induced near-visible band at 420 nm has been identified and is attributed to the creation of an induced boron- oxygen hole center (BOHC) or nonbridging oxygen hole center (NBOHC). FTIR spectra reveal distinct vibrational bands due to triangular (BO3 groups) and tetrahedral (BO4 groups) within their variant characteristic wavenumbers. Also, the condensed intensities of the FTIR bands refer to the sharing of vibrations due to PbO or BiO within their specific sites as evidenced by the deconvoluted spectra. Gamma irradiation causes no variations on the FTIR and ESR spectra confirming the shielding effect of the heavy metal oxides present in mixed percentages.

Unusual Luminescence of Quartz from La Sassa, Tuscany: Insights on the Crystal and Defect Nanostructure of Quartz Further Developments

Quartz luminescence finds applications on many fields, but much work still needs to be done to precisely characterize it. In this work, we made further developments on the study of luminescence of quartz from La Sassa, Tuscany: a sample with unique properties in this regard. Photoluminescence (PL) measurements allowed study of the excitation profile of the previously reported luminescence, showing an excitation maximum at around 4.3 eV, among other minor ones. This kind of luminescence has also been studied as a function of X-ray irradiation, showing that ionizing radiation desensitizes the photoluminescence emissions. New radioluminescence (RL) measurements have been done to study the effect of thermal annealing at 1000 °C, showing a more complex emission picture in the red region (1.8–2.0 eV), with multiple emissions. The data presented here allow more precise assumptions regarding the assignment of the centers responsible for each emission. The assignment has been confirmed by chemical profiles measured by laser-ablation inductively coupled plasma (ICP) mass spectrometry. The previously tentative assignment of non-bridging oxygen hole centers (NBOHCs) has been disproved for the PL and LIF emissions and confirmed for the RL ones.

Study of the Effect of Nitric Acid in Electrochemically Synthesized Silicon Nanocrystals: Tunability of Bright and Uniform Photoluminescence

In this work, we show a correlation between the composition and the microstructural and optical properties of bright and uniform luminescent porous silicon (PSi) films. PSi films were synthesized by electrochemical etching using nitric acid in an electrolyte solution. PSi samples synthesized with nitric acid emit stronger (up to six-fold greater) photoluminescence (PL) as compared to those obtained without it. The PL peak is shifted from 630 to 570 nm by changing the concentration ratio of the HF:HNO3:(EtOH-H2O) electrolyte solution, but also shifts with the excitation energy, indicating quantum confinement effects in the silicon nanocrystals (Si-NCs). X-ray photoelectron spectroscopy analysis shows a uniform silicon content in the PSi samples that emit the strongest PL. High-resolution transmission electron microscopy reveals that the Si-NCs in these PSi samples are about ~2.9 ± 0.76 nm in size and are embedded in a dense and stoichiometric SiO2 matrix, as indicated by the Fourier transform infrared analysis. On the other hand, the PSi films that show PL of low intensity present an abrupt change in the silicon content depth and the formation of non-bridging oxygen hole center defects.

Production mechanism of fluorescent species for calcined zeolite

The fluorescence properties of NH4-form Y-type zeolites calcined under different atmospheres and temperatures were studied. Various analyses were performed on the calcined zeolites to elucidate the origin of the fluorescence. The electron spin resonance spectrum showed two signals corresponding to the E′-center and non-bridging oxygen hole center (NOBHC), which were generated the by collapse of the SiO4 tetrahedron. In the FT-IR spectra, the absorptions assigned to the Si–O vibration peaks decreased in the fluorescent samples. The SiO4 tetrahedron generated fluorescence if it had oxygen vacancy leading SiO3 and/or SiO2 radicals.