Optical transitions associated with gamma-radiation-induced defects in crystalline alpha-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state ...light. After a 10 MGy gamma-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it afterglows in about 100 s at the end of steady-state excitation. The origin of the observed luminescence bands and the comparison with optical features of oxygen-deficient centres in silica glass are discussed in the framework of different models proposed in the literature.
As LPR diagnostic work-up is complex in the absence of a definitive gold standard diagnostic test,
patient symptoms have become a primary method to identify those with LPR. In this regard, Reflux
...Symptom Index (RSI) is a reliable self-administered questionnaire useful also to monitor changes after
treatment. An Italian survey on patients with LPR evaluated the effect of treatments for LPR that were
prescribed in a real-world setting, such as Otolaryngological clinics. In this part of the survey, 1,680
subjects 45.2% males, 54.8% females, 50.4 (14.7) years were visited in the 86 Italian ORL centers. About
70% of patients were treated with Marial® alone, 27% with PPI plus add-on. RSI change assessment was
the primary outcome. Both therapeutic options significantly (p<0.0001) reduced RSI score interestingly
since the second week. The inter-group comparison demonstrated the Marial® monotherapy induced a
greater reduction of RSI than PPI plus add-on since the second week. In conclusion, the present survey
reported that a new medical device (Marial®) may be considered a valid option for the treatment of LPR.
We report that the sintering at 1000°C of silica nanoparticles (an average diameter of 14nm) produces a transparent sample that exhibits a bright visible emission under UV excitation. The use of time ...resolved luminescence spectroscopy and a tunable laser source allows us to single out three contributions centered at 1.96eV, 2.41eV and 3.43eV. The excitation spectra of these emissions evidence bell shaped bands consistent with transitions between localized defects’ states. For each emission we study the intensity and the lifetime in the temperature range from 300K down to 10K, thus evidencing the competition between radiative and non-radiative processes in the optical cycle of luminescent centers. The comparison with the luminescence properties of silica, both nanoparticles and bulk, points out that the observed emissions are peculiar to the sintered silica network.
•Solid-phase sintering at 1000°C of silica nanoparticles produces a transparent sample.•Sintered silica nanoparticles emit a bright luminescence under UV excitation.•Three emissions, centered around 2.0V, 2.4eV and 3.4eV, are distinguished on the basis of the excitation and decay properties.•The observed excitation/emission bands originate from localized defect states peculiar to the sintered silica network.•The luminescence efficiency decreases with temperature due to the activation of non-radiative channels.
The photoluminescence behaviour of carbon-based nanodots is still debated. Both core and surface structures are involved in the emission mechanism, and the electronic transitions can be modified by ...external agents such as metal ions or pH, but the general relation between the structure and the optical function is poorly understood. Here, we report a comparative study on the effects of these variables, changing the core structure from crystalline to amorphous, and modifying the surface structure by different passivation procedures. Our results highlight that the emission mechanism of the tunable visible fluorescence is identical for crystalline and amorphous samples, indicating the independence of the emission from the core structure. Furthermore, surface functionalization weakly influences the emission peak position, but has large consequences on their interaction with different metal ions. This suggests the involvement of quasi-degenerate electronic states originating from the high density of different interacting groups on the surface. Finally, we report the presence of an unusual ultraviolet emission band for the amorphous sample, likely involving localized molecular-type chromophores with carboxyl ends. Our findings provide new information on the emission mechanisms of CDs and can be used to engineer sub-types of CDs displaying very similar emission features, but specifically tailored for different sensing applications.
Pictorial representation of the fluorescence mechanisms proposed for carbon nanodots. Blue: tunable visible emission from surface-delocalized electronic states. Violet: UV emission from localized, quasi-molecular chromophores.
The effects of a high-pressure O 2 -loading treatment on the radiation response of Ge-doped optical fibers (OFs) were investigated. We found that the incorporation of high concentration of ...interstitial molecular oxygen remarkably enhances the resistance to ionizing radiation of Ge-doped OFs in the UV-Visible domain and, at the same time, improves the transmission of UV light in the unirradiated OF sample. By comparison with previously reported results, the O 2 -loading treatment turned out to increase the radiation resistance of Ge-doped OFs more efficiently than F or Ce codoping. The understanding of such amelioration relies in basic radiation-induced mechanisms that were characterized with three complementary experimental techniques: Confocal microluminescence (CML), online radiation-induced attenuation (RIA), and electron paramagnetic resonance (EPR). We have shown that the almost intrinsic oxygen-deficient character of germanosilicate fibers can be overturned by forcing O 2 diffusion in the glass matrix. The Germanium lone pair centers, which are precursor defects invariantly present in the as-drawn Ge-doped OFs, are converted to some other yet-undetermined species. Consequently, the usual chain of radiation-activated processes leading to the creation of Ge(1) and Ge(2) is substantially suppressed. The experiments have also highlighted an increased production of oxygen-excess related defects under irradiation. Although in terms of RIA, the tradeoff between the oxygen-excess and oxygen-deficient defects is already a positive one, it is conceivable that the radiation resistance of Ge-doped OFs can be further improved by optimizing the O 2 -loading treatment.
We report an electron paramagnetic resonance (EPR) study of gamma rays irradiation effects on an oxygen-deficient silica obtained from fused quartz. We have found that three types of E′ centers,
E
α
...′
,
E
γ
′
and
E
δ
′
, and a paramagnetic defect in a spin triplet state (
S
=
1) are induced. The EPR signals dependence on the microwave power have been investigated. The concentrations of these centers as a function of gamma ray irradiation show that for high dose a limit value is reached suggesting a generation process from precursors.
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