Search

Abstract This study aims to learn more about the structure of densified silica with focus on the metamict-like silica phase (density = 2.26 g/cm3) by examining the formation of E’ point defects and interstitial molecular oxygen O2 by 2.5 MeV electron irradiation. High-dose (11 GGy) irradiation creates a metamict-like phase and a large amount of interstitial O2, which is destroyed upon subsequent additional lower-dose electron irradiation. The O2 cathodoluminescence (CL) data indicate that the formation of O2 from peroxy linkages Si–O–O–Si in silica network is strongly dependent on the intertetrahedral void sizes. The position and shape of the O2 emission line support the idea that the configuration of these voids in metamict phase is close to that of non-densified silica. Moreover, data support the strong correlation between the formation of 3-membered rings of Si–O bonds and E’-centers when silica density increases from 2.20 to 2.26 g/cm3.

Scintillator materials are widely used for a variety of applications such as high energy physics, astrophysics and medical imaging. Since the ideal scintillator does not exist, the search for scintillators with suitable properties for each application is of great interest. Here, Pr 3+ -doped KGd(PO 3 ) 4 bulk single crystals with monoclinic structure (space group: P2 1 ) are grown from high temperature solutions and their structural, thermal and optical properties are studied as possible candidates for scintillation material. The change in the unit cell parameters as a function of the Pr 3+ level of doping and temperature is studied. Differential thermal analysis reveals that KGd 0.942 Pr 0.058 (PO 3 ) 4 is stable until 1140 K. The 5d 3 , 5d 2 and 5d 1 levels of Pr 3+ with respect to the 3 H 4 ground state are centred at 166, 196 and 218 nm, respectively, in this host. The luminescence of KGd 0.990 Pr 0.010 (PO 3 ) 4 , by exciting these 5d levels, shows intense emissions centred at 256 and 265 nm from the 5d 1 to 3 F 3,4 and 1 G 4 levels of Pr 3+ with a short decay time of 6 ns. The 6 P 3/2,5/2,7/2  →  8 S 7/2 transitions of Gd 3+ appear after exciting the 5d levels of Pr 3+ and the 4 f levels of Gd 3+ , showing an energy transfer between Pr 3+ and Gd 3+ .

Sorption mechanism of uranyl by poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MP) functionalised polyvinylidene fluoride (PVDF) track-etched membranes, PB2MP-g-PVDF, was investigated. It was found that uranyl sorption obeyed Langmuir isotherm model giving a maximum U(VI) membrane uptake of 6.73 μmol g -1 and an affinity constant of 9.85 ⋅ 10 6 L mol -1 . XPS and TRPL measurements were performed to identify sorbed uranyl oxidation state and its environment. Uranyl was found to be mainly in its hexavalent state, i.e. U(VI), showing that the trapping inside the PB2MP-g-PVDF nanoporous membranes did not change the ion speciation. Two sorbed uranyl life-times (τ 1 = 8.8 μs and τ 2 = 102.8 μs) were measured by TRPL which pointed out different complexations taking place inside the nanopores. Uranyl sorption by PB2MP-g-PVDF membranes was also found to be pH dependent demonstrating the highest performance at circumneutral pH. In addition, TRPL was demonstrated to be not only a remarkable technique for U(VI) characterization, but also an alternative to voltammetry detection for trace on-site uranyl monitoring using PB2MP-g-PVDF nanoporous membranes.

We examined the "relaxation properties" of pre-densified synthetic fused silica glass under 2.5 MeV electron irradiation. The densification of the glass was either obtained by hot compression (5 GPa-350 °C and 5 GPa-1000 °C) or via a thermal treatment increasing its fictive temperature (T f  = 1050, 1250 and 1400 °C). Under irradiation, the pre-densified silica glasses exhibit a relaxation of their macroscopic density with increasing integrated dose. Density was reduced for hot compressed silica and increased for T f samples with different relaxation rates but it is remarkable that all sample densities follow a trend towards the same equilibrium value around 2.26 for a dose larger than 10 GGy despite a different final topology. After irradiation of hot compressed silica, the Raman spectra display a significant increment of 4 and almost 3-membered rings whereas they exhibit a glass density reduction; demonstrating that a D 2 band increase cannot be considered as an absolute marker of the glass compaction. The correlation between density and D 2 intensity remains valid until silica density remains lower than 2.26. In contrast, the FWHM of the main band peaking at 440 cm -1 appears to remain correlated to the silica glass density for all investigated samples.

Scintillator materials have gained great interest for many applications, among which the medical applications stand out. Nowadays, the research is focused on finding new scintillator materials with properties that suit the needs of each application. In particular, for medical diagnosis a fast and intense response under high-energy radiation excitation is of great importance. Here, type III Ce 3+ -doped KGd(PO 3 ) 4 single crystals with high crystalline quality are grown and optically characterized as a new promising scintillator material. The 4f → 5d electronic transitions of Ce 3+ are identified by optical absorption. The optical absorption cross section of Ce 3+ for the electronic transition from the 2 F 5/2 to the 5d 1 level is 370 × 10 -20  cm 2 . The luminescence of KGd 0.996 Ce 0.004 (PO 3 ) 4 crystal by exciting the 5d levels of Ce 3+ with VUV-UV synchrotron radiation shows down-shifting properties with strong emissions at 322 and 342 nm from the 5d 1 to 2 F 5/2 and 2 F 7/2 levels of Ce 3+ with a short decay time of ~16 ns, which is very suitable for scintillator applications. Moreover, these intense emissions are also observed when Gd 3+ is excited since an energy transfer from Gd 3+ to Ce 3+ exists.