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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.

Zirconium nitride (ZrN) is widely used in many industrial sectors for its outstanding performances including its mechanical properties, high chemical and thermal stability. Associated with its plasmonic behavior, these properties make ZrN a suitable candidate for optical applications at high temperature or in extreme environments. The authors present an innovative, easy-to-use and rapid process for producing ZrN thin films from a photo-structurable ZrO2 sol-gel using a rapid thermal nitridation (RTN) process. In this process, a ZrO2 sol-gel layer is converted into a ZrN thin film in a few minutes by rapid thermal annealing (RTA) under ammonia gas. Compared to physical or chemical vapor deposition, usually used to produce ZrN thin films, the advantages of the sol-gel method include suitability for non-planar and large substrates and the possibility of nanotexturing of crystallized ZrN surfaces in considerably less time, at a larger scale and at a lower cost. The ZrO2 and ZrN thin films were characterized by Raman spectroscopy, X-ray diffraction and Transmission Electron Microscopy, to confirm complete nitridation. The optical, electrical and tribological properties were also investigated. Finally, the nitridation method was also used on structured ZrO2 layers and showed the versatility of the process e.g. enabling the production of micro-nanostructured ZrN films without using any etching techniques.

This study investigates the structural and optical responses of silica glass to femtosecond (fs) laser irradiation followed by high-energy electron (2.5 MeV, 4.9 GGy) irradiation. Using optical microscopy and spectroscopy techniques, we analyzed retardance, phase shifts, nanograting periodicity, and Raman D 2 band intensity, which is an indicator of local glass densification. S-SNOM and nano-FTIR measurements further revealed changes in the Si-O-Si vibrational bands, indicating partial relaxation of the densified nanolayers under electron irradiation. Our findings reveal significant optical modifications due to subsequent electron irradiation, including reduced retardance and phase values, which are in agreement with the relaxation of the local densification. SEM analysis confirmed the preservation of nanogratings' morphology including their periodicity. Apart from revealing fundamental aspects related to glass densification within nanogratings, this study also underscores the potential of combined fs-laser and electron irradiation techniques in understanding silica glass behavior under high radiation conditions, which is crucial for applications in harsh environments.

This study explores the structural transformations induced by femtosecond (fs) laser inscriptions in glass, with a focus on type II modifications (so-called nanogratings), crucial for advanced optical and photonic technologies. Our novel approach employs scattering-type scanning near-field optical microscopy (s-SNOM) and synchrotron radiation nanoscale Fourier-transform infrared spectroscopy (nano-FTIR) to directly assess the nanoscale structural changes in the laser tracks, potentially offering a comprehensive understanding of the underlying densification mechanisms. The results reveal the first direct nanoscale evidence of densification driven by HP-HT within fs-laser inscribed tracks, characterized by a significant shift of the main infrared (IR) vibrational structural band of silica glass. It reveals moreover a complex interplay between type I and type II modifications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this study, we investigate the effects of densification through high pressure and temperature (up to 5 GPa, 1000 °C) in the making of nanogratings in pure silica glass, inscribed with femtosecond laser. The latter were monitored through retardance measurements using polarized optical microscopy, and their internal structure was observed under scanning electron microscopy. We reveal the difficulty in making nanogratings in densified silica glasses. Based on this observation, we propose that free volume may be a key precursor to initiate nanograting formation.

Fluorine-doped silica is a key material used in all low-loss and/or radiation-resistant optical fibers. Surprisingly, no fluorine-related radiation-induced point defects have been identified. By using electron paramagnetic resonance, we report the first observation of F-related defects in silica. Their fingerprint is a doublet with 10.5 mT splitting due to hyperfine coupling (hfc) to ^{19}F nuclear spins. An additional 44.4 mT hfc to the ^{29}Si nucleus indicates that this defect belongs to the "E^{'} center" family and has a structure of a fluorine-modified Si dangling bond: 3-coordinated Si atoms with an unpaired electron in an sp^{3} orbital, bonded to a glass network by 2 bridging oxygen atoms and to a F atom.

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.

In the interphase cell nucleus, chromosomes adopt a conserved and non-random arrangement in subnuclear domains called chromosome territories (CTs). Whereas chromosome translocation can affect CT organization in tumor cell nuclei, little is known about how aneuploidies can impact CT organization. Here, we performed 3D-FISH on control and trisomic 21 nuclei to track the patterning of chromosome territories, focusing on the radial distribution of trisomic HSA21 as well as 11 disomic chromosomes. We have established an experimental design based on cultured chorionic villus cells which keep their original mesenchymal features including a characteristic ellipsoid nuclear morphology and a radial CT distribution that correlates with chromosome size. Our study suggests that in trisomy 21 nuclei, the extra HSA21 induces a shift of HSA1 and HSA3 CTs out toward a more peripheral position in nuclear space and a higher compaction of HSA1 and HSA17 CTs. We posit that the presence of a supernumerary chromosome 21 alters chromosome compaction and results in displacement of other chromosome territories from their usual nuclear position.

Yb 3+ /Al 3+ /P 5+ -co-doped silica glasses with different P/Al ratios were prepared using the sol-gel method combined with high-temperature sintering. The evolution of composition-dependent color centers caused by X-ray irradiation in these glasses was correlated with their structural changes, which are controlled by the P/Al ratio. Nuclear magnetic resonance (NMR) and Raman spectra have been used to characterize the glass network structure, and advanced pulse electron paramagnetic resonance (EPR) has been employed to study the local coordination atomic structures of Yb 3+ ions in pristine glasses as a function of the P/Al ratio. Si- (Si-E'), Al- (Al-E', Al-ODC, AlOHC), P- (P 1 , P 2 , POHC), and Yb-related (Yb 2+ ) color centers in irradiated glasses have been observed and explained by optical absorption and continuous wave-EPR spectroscopies. The formation mechanisms of these centers, the structural models of glasses, and the relationship between them were proposed. Direct evidence confirms that the formation of Yb 2+ ions induced by radiation is highly dependent on the coordination environment of Yb 3+ ions in glasses. In addition, the glass network structure significantly affects the generation of oxygen hole color centers (AlOHCs/POHCs) caused by radiation. These results are useful in understanding the microstructural origin and the suppression mechanism of the radiodarkening effect by phosphorus co-doping in Yb 3+ -doped silica fibers.

Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb 3+ -doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb 3+ /Al 3+ /F - /P 5+ -co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al 3+ /F - /P 5+ in Yb 3+ -doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb 3+ . The spectroscopic properties of Yb 3+ ions have not deteriorated by the co-doping of F - and P 5+ in YAFP glass compared with that of Yb 3+ /Al 3+ co-doped silica glass. A large-size (⌀5 mm × 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 × 10 -4 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10 -4 , was prepared. A LMA PCF with 50 µm core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M 2 of 1.4.

The determination of very low doping levels in solid materials is an important issue for many applications. When considering paramagnetic dopants, the NMR relaxation technique appears to be much more accurate than classical techniques such as Vegard's law resulting from X-ray diffraction (XRD) measurements or chemical analysis that cannot provide information on appropriate dopant spatial distributions. In a recent report, the linear variation of 1/T 1 , i.e. the nuclear relaxation rate, as a function of Nd 3+ content has been used to determine doping levels with a good dispersion homogeneity in the monazite LaPO 4 matrix down to 0.1 mol%. We here extend this study to more complex compounds doped with Nd 3+ , such as YPO 4 , the solid solution Y 0.8 Sc 0.2 PO 4 , Ba 5 (PO 4 ) 3 Cl and a phosphate glass. For all considered compounds except Ba 5 (PO 4 ) 3 Cl:Nd, 1/T 1 is found to be linearly proportional to the nominal Nd concentration, confirming the ability of the method to investigate the dopant concentration and spatial homogeneity. The results obtained for different compounds open up the discussion on the parameters, such as the orbital overlap and the average P-P distances, influencing the nuclear relaxation rate.

The impact of fictive temperature (T f ) on the evolution of point defects and optical attenuation in non-doped and Er 3+ -doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of erbium salt-soaked nanoporous silica xerogels through the polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by FTIR, UV-vis-NIR absorption spectroscopy, electron paramagnetic resonance, and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV-vis range. Furthermore, it was found that γ-radiation "hardness" is higher in Er 3+ -doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction.

This Letter relates the clear evidence of Yb 2+ formation under 2.5 MeV electron irradiation in optical fiber preforms showing a darkening of the core. We thus detected by in situ photoluminescence measurements the green emission of divalent Yb 2+ under the 355 nm excitation. Moreover, we showed the existence of two types of Yb 2+ ion species with different stabilities. We demonstrated that the radiodarkening mechanism is based on a pair association of Yb 2+ with aluminum oxygen hole center point defects.

Rare earth doped active glasses and fibers can be exposed to ionizing radiations in space and nuclear applications. In this work, we analyze the evolution of (2)F(5/2) excited state lifetime in Yb(3+) ions in irradiated aluminosilicate glasses by electrons and γ rays. It is found that the variation of lifetimes depends on the Yb(3+) clusters content of the glasses for irradiation doses in the 10(2)- 1.5∙10(9) Gy range. In particular, glasses with high clustering show a smaller decrease in lifetime with increasing radiation dose. This behavior is well correlated to the variation in paramagnetic defects concentration determined by electron paramagnetic resonance. This effect is also observed in Yb(3+) doped phosphate and Er(3+) doped aluminosilicate glasses, inferring that clustering plays an important role in irradiation induced quenching.

This Letter demonstrates a remarkable interplay between photo- and radiation-induced darkening of ytterbium-doped alumino-silica optical fibers operated in amplifying conditions and harsh environments (as, e.g., in space-based applications). Influences of the pump power, ionizing dose, and dose rate on this interaction are characterized. The pump is capable of accelerating or slowing down the radiation-induced darkening build-up depending on the ionizing dose. The steady-state photo-radio-darkening level is independent of the dose and at least equal to the equilibrium level of pure photo-darkening. This lower limit is notably reached at low dose rates, including those encountered in space. We, therefore, argue that photo-resistant ytterbium-doped fibers will resist against a space mission, whatever the dose.

One-, two- or three-dimensional arrays of closely spaced silver nanoparticles may lead to new optical properties, due to short or long range coupling between their resonant surface plasmons, so that the spatially controlled growth of silver nanoparticles provides an efficient way to tune their optical properties. Towards this way, we present here the periodic pattern of a glass surface with silver nanoparticles by continuous ultraviolet laser exposure. The formation of the 160 nm period pattern is well described by an interference-based model which agrees with the experimental conclusions, mainly obtained by various forms of microscopy. Statistical approach based on the autocorrelation function gives quantitative description about the quality of the order in the periodic structure and about the nanoparticles averaged diameter (80 nm). We also present the optical extinction spectrum of the Laser Induced Periodic Surface Structure (LIPSS)-containing area of the glass, which unusually shows several bands in the visible range. The period of 160 nm of the periodic structure is short enough to allow coupling between nanoparticles, which makes it a possible candidate for plasmon-based optical applications.

Using a combination of experimental techniques such as optical absorption, Raman scattering, continuous wave and pulse Electron Spin Resonance (ESR), we characterize a set of γ-irradiated Yb(3+) doped silica glass preforms with different contents of phosphorous and aluminum. We demonstrate that when P is introduced in excess compared to Al, nearly no radiodarkening is induced by γ-rays. On the other hand, when Al>P, a large absorption band is induced by radiation. Thermal annealing experiments reveal the correlation between the decrease of the optical absorption band and the decrease of the Al-Oxygen Hole Center (AlOHC) ESR signal, demonstrating the main role of AlOHC defects in the fiber darkening. HYSCORE (HYperfine Sublevel CORElation) pulse-ESR experiments show a high Al-P nuclear spin coupling when P>Al and no coupling when Al>P. This result suggests that both AlOHC and POHC creation is inhibited by Al-O-P linkages. Confronting our data with previous works, we show that the well-known photodarkening process, meaning losses induced by the IR pump, can also be explained in this framework.

Using a combination of pulse electron paramagnetic resonance and photoluminescence spectroscopy, we demonstrate the major role of phosphorous rather than aluminium in the rare-earth dissolution process, an essential advance in telecommunication and solid laser fields. Our results also provide new insight into the micro-structural origin of the photodarkening process occurring in Yb doped fiber.