Oxygen Hole Centers Research Articles

Impact effects of gamma irradiation on the optical and FT infrared absorption spectra of some Nd3+–doped soda lime phosphate glasses

The main aim of the present work is to study by two collective optical and FTIR spectral measurements some prepared Nd2O3–doped soda lime phosphate glasses before and after gamma irradiation with dose (9 Mrad). The spectral data reveal two strong UV absorption peaks which are correlated with unavoidable trace iron impurities beside extended additional characteristic bands due to Nd3+ ions. Gamma irradiation on the undoped glass produces slight decrease of the intensity of the UV absorption and the generation of an induced visible band and these effects are controlled with two photochemical reduction of some Fe3+ ions to Fe2+ ions together with the formation of nonbridging oxygen hole center (NBOHC) or phosphorous oxygen hole center (POHC). The impact effect of gamma irradiation on the spectra of Nd2O3–doped glasses is limited due to suggested shielding behavior of neodymium ions. FT–infrared spectra show vibrational modes due to main Q2–Q3 phosphate groups and the response of gamma irradiation of the IR spectra is low and the limited variations are related to suggested changes in some bond angles and bond lengths which cause the observed decrease to the intensities of some IR bands.

Impact of glass density on the green emission and NBOHC formation in silica glass: A combined high pressure and 2.5 MeV electron irradiation

Macroscopic Suprasil F300 type silica glasses densified under high pressure and high temperature were irradiated with 2.5MeV electrons. This paper focuses on the point defects generation in those densified silica glasses. We demonstrated that the unattributed 540nm emission band was clearly enhanced when the irradiated glasses exhibit a higher density either initially generated by high pressure cycle or by irradiation at high dose (>3GGy). The spectral shape of the emission band related to Non Bridging Oxygen Hole Center (NBOHC) is also modified with a broader FWHM due to an additional contribution near 610nm indicating a larger distribution of NBOHC species in these densified glasses.

Femtosecond laser processing induced low loss waveguides in multicomponent glasses

We have investigated that femtosecond laser induced optical waveguides in AF32 and in Borofloat-33 glasses. Type-I positive and type-II negative refractive index change mechanisms were established in AF32 and in Borofloat-33 glass waveguides, respectively. Lowest propagation loss of 1.1 ± 0.31 dB/cm could be attained in AF32 glass, which has a typically higher index change than in Borofloat-33 glass. Resultant losses are directly correlated with densification and non-bridging oxygen hole centers, which can be authenticated by Raman and photoluminescence studies.

Cathodoluminescence response of natural and synthetic lanthanide-rich phosphates (Ln3+: Ce, Nd)

This paper reports on the cathodoluminescence (CL) emission of both natural and synthetic lanthanide-rich phosphates (Ln3+: Ce, Nd) previously characterized by X-ray Diffraction (XRD), Environmental Scanning Electronic Microscopy (ESEM) and Energy Dispersive Spectroscopy. The thermal treatment at 700°C performed on the synthetic sample obtained by chemical precipitation, promotes increasing of the crystallinity degree giving rise to a phase transition from the hexagonal (comprising monazite and rabdophane) into the monoclinic (cerianite and monazite) structures detected by XRD. Despite the size and the morphology of the grains are similar under ESEM, it could be appreciated significant differences among CL signals attending to the shape (with well-defined peaks for the annealed sample) and intensity (with lower emission for the non-thermally pretreated synthetic phosphate). The main wavebands centered at (i) 360, 380 and 490nm are associated respectively with 5D3/2 → 2F5/2 and 5D3/2 → 2F7/2 transitions as well as a redox reaction assigned to the presence of Ce3+, (ii) 276, 424, 516 and 531nm are linked respectively to 2G9/2→4I9/2, 2P1/2→4I9/2, 4G9/2→4I9/2 and 4G7/2→4I9/2 Nd3+ transitions and (iii) 400–490nm is due to non-bridging oxygen hole centers related to the tetrahedral PO43- groups or structural defects for the heated synthetic samples. The natural sample from Madagascar, with a very complex CL spectrum, displays a characteristic band emission in the green-yellow and red regions corresponding to [UO2]2+ groups and Sm3+ respectively.

Using NBOHC fluorescence to predict multi-pulse laser-induced damage in fused silica

We investigate the evolution of the fluorescence signal as function of repeated nanosecond laser pulses up to laser-induced damage in fused silica at 266 nm. We observed a maximum in the fluorescence spectrum at 664 nm linked to NBOHCs (Non-Bridging Oxygen Hole Centers). This peak increases with shot number for a fixed fluence until damage occurs. Thanks to the data from the in situ fluorescence measurements, we propose a new method to predict the occurrence of laser damage in high quality fused silica samples like Herasil©and Suprasil 1©. This new method allows to reduce drastically the time of test and the area under study that are required to record the reference data for damage occurrence. Furthermore we measured that the lifetime of the laser-induced modifications is about 2 h in Herasil.

Systematic control of optical features in aluminosilicate glass waveguides using direct femtosecond laser writing

Low loss optical waveguides inside aluminosilicate glasses have been successfully fabricated using direct femtosecond laser writing. To establish the influence of pulse energy and host variations on the optical waveguides have been tentatively explored and systematically studied with the help of different spectroscopic techniques. Isochronal annealing treatment effectively reduces the insertion losses to 1.01 ± 0.28 dB at 632.8 nm. A red shift of the Raman band has been observed with increasing Al2O3 content due to the bond angle variations. The point defects such as non-bridging oxygen hole centers have been corroborated by the photoluminescence studies and significant red-shift has also been documented with increasing Al2O3 content. In addition, there is no NBOHC defects perceived after isochronal annealing treatment inside the glass waveguides. Our results envisage that the present glass waveguides should be promising and potential for applications in passive waveguides and integrated photonic devices.

Optical, FTIR and ESR Spectral Investigations of Tungsten Ions in Barium Phosphate Host Glass and Effects of Gamma Irradiation

Tungsten oxide (0.25 – 3% WO3) doped barium phosphate glasses were prepared by the conventional melting annealing procedure. Spectroscopic FTIR infrared and ESR measurements were applied at 0 and 10 Mrad doses of gamma irradiations. The UV-Visible spectrum of the base glass consists of distinct ultraviolet peaks that can be correlated with trace ferric (Fe3+ ions) impurities. UV-Visible absorption spectra of WO3 – doped glasses show similar ultraviolet absorption as the base glass and a very broad visible band settled at about 720 nm and with the high content sample (3% WO3) two peaks are identified at 602 and 790 nm on the very broad visible absorption band. These additional broad band accompanied by the bluish color to the samples support the assumption of the formation or presence of pentavalent tungsten ions because of the reducing nature of the phosphate host glass. Gamma irradiation produces some extension of the UV absorption of the undoped glass spectrum accompanied by the generation of an induced visible broad band centered at 520 nm. These extra induced changes are related to some photochemical reactions leading to the partial oxidation of some ferrous ions to ferric ions through the radiation effect. The induced broad visible band is assumed to be related to the formation of phosphorus oxygen hole centers (POHC) or nonbridging oxygen hole centers (NBOHC) from interaction of gamma rays on the phosphate network. Gamma irradiation of WO3 doped glasses reveals the increase of the intensity of the very broad band and in the high content sample (3% WO3), a new induced band is generated at about 411 nm. These changes are assumed to be related to some photochemical reactions involving the conversion of some W6+ ions to W5+ ions by capturing electrons or by photo-reduction of W6+ ions to W4+ ions and thus imparting the additional peak at 411 nm. FTIR results of the studied glasses reveal the appearance of vibrational modes due to phosphate network groups mainly of metaphosphate units or P–O–P linkages as the response of the chemical composition 50% BaO – 50% P2O5. The infrared results of the radiative samples have no notable changes due to compactness of the phosphate with noticeable amount of heavy Ba2+ ions which seem to retard the passage of liberated electrons or positive holes during the irradiation process and thus the network structure remains unaffected. ESR spectra of WO3 – doped glasses reveal distinct signals due to the unpaired pentavalent ions which are stable towards irradiation due to the existence of a high content of the heavy Ba2+ ions which block the passage of negative and positive holes during irradiation.

Quartz modification by Zn ion implantation and swift Xe ion irradiation

The quartz slides were implanted by 64Zn+ ions with dose of 5 × 1016/cm2 and energy of 100 keV. After implantation, the amorphous metallic Zn nanoparticles with an average radius of 3.5 nm were created. The sample surface becomes nonuniform, its roughness is increased and its values rise up to 6 nm compared to virgin state, and the roughness maximum is at a value of about 0.8 nm. The surface is made up of valleys and hillocks which have a round shape with an average diameter about 200 nm. At the center of these hillocks are pores with a depth up to 6 nm and a diameter of about 20 nm. After implantation in UV‐vis diapason, the optical transmission decreases while PL peak (apparently due to oxygen deficient centers) at wavelength of 400 nm increases. Then the samples were subjected to swift Xe ion irradiation with the fluences of 1 × 1012–7.5 × 1014/cm2 and energy of 167 MeV. After Xe irradiation, the sample surface roughness shat down to values of 0.5 nm and the roughness maximum is at a value of about 0.1 nm. Optical transmission in UV‐vis diapason increases. The PL peak at wavelength of 400 nm is decreased while a PL peak at wavelength of 660 nm is raised. This peak is presumably due to non‐bridging oxygen hole centers or/and NPs with structure Si(core)/SiO2(shell).HRTEM image of Zn‐implanted quartz subsurface layer. One can see the Zn amorphous nanoparticles, which confirms the electron diffraction pattern (insert).

Coupled irradiation-temperature effects on induced point defects in germanosilicate optical fibers

We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results on samples X-ray irradiated at 5 kGy(SiO2), employing different temperatures and dose rates, are reported and discussed. The data highlight the generation of the Ge(1), Ge(2), E′Ge and E′Si defects. For the Ge(1) and Ge(2), we observed a decrease in the induced defect concentrations for irradiation temperatures higher than ~450 K, whereas the E′ defects feature an opposite tendency. The comparison with previous post-irradiation thermal treatments reveals peculiar effects of the temperature increase during the irradiation. Such difference, confirmed also by online radiation-induced attenuation measurements, has to be considered for practical use of these fibers in a mixed environment. Importantly, even if post-irradiation fading should be considered, the Ge(1) and Ge(2) concentrations measured by postmortem EPR experiments in room-temperature-irradiated samples are quite representative of the concentrations induced in the temperature range 230–450 K regardless of the investigated dose rate. The enhancement of the E′ content can be related to the simultaneous generation of this defect with non-bridging oxygen hole center from strained bonds implying a relevant modification of the defects generation/formation processes in the host glass matrix.

Gamma rays Interactions with Bismuth Phosphate Glasses Doped with 3d Transition Metal Oxides

Bismuth phosphate glasses of the basic composition (Bi2O3 30 mol%-P2O5 70 mol%) with additional dopants 3d TM oxides (0.2 wt%) were prepared by the melting and annealing technique. Combined optical (UV/vis.) and FT infrared absorption spectra were measured for the prepared samples before and after gamma irradiation with a dose of 8 Mrad (8×104 Gy). Optical spectra reveal strong UV absorption bands due to trace iron impurity together with an additional absorption band due to Bi3+ beside characteristic absorption related to specific 3d TM ions with preference for the lower valences due to the reducing effect of phosphate host glass. FTIR spectra show vibrational bands due to phosphate chains with the sharing of absorption bands due to Bi-O vibrations. Gamma irradiation causes limited changes due to the presence of heavy metal Bi3+ ions which show some shielding behavior towards gamma irradiation as revealed by optical and FT infrared absorption measurements. Some suggested photochemical reactions are forward to interpret the changes in the UV spectra beside the formation of an induced phosphorus oxygen hole center (POHC) in the visible region.

21‐3: Reliability of Coplanar Oxide TFTs : Analysis and Improvement

We confirm that the PBTS instability of coplanar InGaZnO TFTs can be improved through the minimization of Non‐Bridging Oxygen Hole Centers (NBOHC) and optimization of hydrogen passivation in the GI/ACT interface region. The quantitative analysis of hydrogen and oxygen in each region are obtained from physical property measurements. Trap density in GI/ACT interface layer is obtained by photonic capacitance‐voltage measurements which are correlated with PBTS characteristics. A decrease of under coordinated bonding states lessens electron trap density, which brings improvement in PBTS from Vth = 2.61V to 0.21V by process optimization.

Cathodoluminescence of moldavites

AbstractA systematic study of a large set of moldavites and the application of cathodoluminescence (CL)‐spectroscopy with a detailed discussion of spectral features is presented. Optical CL microscopy and spectroscopy (OM‐CL) were performed on 57 moldavite samples from different substrewn‐fields in Germany and the Czech Republic. The extracted CL data were supported by SEM‐EDX analysis. In general, two different kinds of CL colors can be distinguished: different shades of green in the matrix of the tektite glasses and a variation of blue color for lechatelierite inclusions (a pure silica‐glass phase). Spectral analysis of these colors shows three CL emission bands for green and five bands for blue c. Most CL activators are structural defects of the local glass network, influenced by the crystal field. The visible green CL emission is caused by defects related to strong local disorder as well as Al‐O−‐Al defects. The blue CL emission is activated by different types of lattice defects such as nonbridging oxygen‐hole center (NBOHC), self‐trapped excitons (STE), and oxygen deficiency centers (ODC). Intensity variations of the CL emissions were observed for samples from the different localities, but there is no direct correlation between substrewn‐fields and CL characteristics. Nevertheless, CL microscopy is a powerful tool for the high‐contrast visualization of internal textures such as streaks and lechatelierite in the tektite matrix due to the luminescence properties of the defect structures in the glassy network.

Study on the phase transition of fracture region of laser induced damage in fused glass by focused nanosecond pulse

As a key optical material in high-energy laser system, the laser induced damage of fused silica glass has been one of the bottlenecks to limit output of the laser influence. In this paper, the morphology of fractures on fused silica glass surface as well as phase transition caused by laser pulse shock wave have been investigated in theory and experiment, and we found that the whole fracture region can be divided into hackle zone, mist zone and mirror zone, which were produced by the tip of hoop stress formed in glass under the action of laser plasma shock wave. During cracks initiating and propagating of fused silica glass, the existing of cracks can reduce the relative content of three- and four-number rings structures corresponding to the stishovite and the coesite which caused by the absence oxygen free, this kind of change may destroy the mesh topology severely, and induce phase transitions. From the micro level, the non-bridging oxygen hole center and E' center lead to the decrease of the optical band gaps as well as transmittance which seriously affect the performance of glass.

Irradiation temperature effects on the induced point defects in Ge-doped optical fibers.

We present an experimental investigation on the combined effects of temperature and irradiation on Ge-doped optical fibers. Our samples were X-ray (10 keV) irradiated up to 5 kGy with a dose rate of 50 Gy(SiO2)/s changing the irradiation temperature in the range 233-573 K. After irradiation we performed electron paramagnetic resonance (EPR) and confocal microscopy luminescence (CML) measurements. The recorded data prove the generation of different Ge related paramagnetic point defects and of a red emission, different from that of the Ge/Si Non-Bridging Oxygen Hole center. Furthermore, by comparing the behaviour of the EPR signal of the Ge(1) as a function of the irradiation temperature with the one of the red emission we can exclude that this emission is originated by the Ge(1).

Study of Radiation Effects on Er3+-Doped Nanoparticles Germano-Silica Fibers

The main goal of the present work is to study the impact of Er–SiO2 and Er–Al2O 3 nanoparticles on the radiation induced defects in germano-silica optical fibers with Al/Ge ranges over 0.1–150. These fibers are prepared by a modified chemical vapor deposition technique and are characterized by optical absorption and electron paramagnetic resonance spectroscopy. High amount of Ge, Er–SiO2 nanoparticles-derived optical fibers exhibit lower radiation induced attenuation than those with a low Ge content undoped or doped with Al2O3 nanoparticles. Furthermore, the behavior of point defects namely GeE’, Ge(1), SiE’, nonbridging oxygen hole centers, and H(1) is reported according to the Al/Ge ratio. In contrast to the optical fiber preforms, no Al-related defects are found in the optical fibers. Therefore, the results evidence the strong radiation tolerance by the virtue of the nanoparticle doping, which is enabling technology for the development of the photonic and space applications in the radiation fields.

In Situ Luminescence Measurement from Silica Glasses Irradiated with 20 keV H− Ions

A new low-energy negative-ion induced luminescence setup was recently developed at the injector of the GIC4117 2 × 1.7 MV Tandem accelerator in Beijing Normal University. In situ luminescence measurements are performed on silica glass by using 20keV H− ions at room temperature. Gauss fitting of the spectra revealed six overlapping components at about 2.7 eV, 2.4eV, 1.9eV, 1.8eV, 4.2eV, and 3.6eV, which except for the new observed emission band at 3.6 eV are assigned to the creation of type II oxygen-deficient centers, E' centers, non-bridging oxygen hole centers with different precursor states, and type-I oxygen-deficient centers. The fitted results of the saturation concentration show that self-trapped exciton recombination at type-II oxygen-deficient centers is the main luminescence emission process. The evolution of the luminescence intensity and full width at half maximums as a function of ion fluence is also discussed. It is found that the number of recombination centers reaches its maximum at lower fluence, and the area ratio between blue bands and red bands is much lower than that under high energy H+ ion irradiation.

Optical character enrichment of NdF3 – doped lithium fluoroborate glasses

Optical spectra in combination with Fourier transform infrared FTIR spectra of base undoped lithium fluoroborate glasses and samples that doped with NdF3 were measured before and after subjecting to (8Mrad) gamma irradiation. Base glass reveals strong absorption in the UV region attributed to unavoidable iron impurity (Fe3+ ions) while gamma irradiated sample shows extended additional peaks related to the photochemical reactions of some Fe2+ impurities transformed to Fe3+ ions by acquiescent positive holes while the induced visible band is related to (BOHC) boron oxygen hole center or (NBOHC) nonbridging oxygen hole center. The NdF3-doped samples display the same strong UV spectra as the undoped sample beside additional characteristic visible absorption peaks due to the presence of Nd3+ ions. UV–Vis. absorption spectra were applied to assess their optical properties, comprising indirect and direct optical energy band gaps taking into account the effect of gamma irradiation. Infrared absorption spectra of the undoped lithium fluoroborate glass reveal characteristic IR bands due to both BO3 and BO4 borate groups as usually observed in various alkali–oxide B2O3 glasses. Suggested BO3F tetrahedral units are advanced to interpret the close similarity of the IR spectra obtained from fluoroborate glass with alkali or alkaline earth oxide borate glasses. The increase of NdF3 content causes minor changes in the IR spectra that can be attributed to the non-conventional loose OH, H2O or similar vibrations while the structural building borate units remain unchanged as evidence from the deconvoluted FTIR data before and after the irradiation process.

Bioactivity characterization of 45S5 bioglass using TL, OSL and EPR: Comparison with the case of 58S sol-gel bioactive glass

The current work exploits the effective application of thermoluminescence (TL), optically stimulated luminescence (OSL) and the possibility of applying Electron Paramagnetic Resonance (EPR) for the discrimination between different bioactive responses in the case of the 45S5 bioactive glass (SiO2 45, Na2O 24.5, CaO 24.5, P2O5 6 in wt%), which was synthesized through melting process. These techniques are suggested mainly due to their low spectroscopic detection thresholds. The original 45S5 in grain size range of 20–40μm was immersed in the Simulated Body Fluid (SBF) for various different immersion times ranging over one week. In this work the 110°C TL peak, a specific OSL component and the EPR signal at g=2.013 ascribed to oxygen hole center (OHC) are used due to their sensitivity to the different bioactive responses. For all luminescence and EPR components, the intensity plot versus immersion time yields sharp discontinuities, resulting in effective probes regarding the timescale for both the beginning as well as the end of the procedure of the crystalline HCAp formation respectively. On the contrary to the smooth decreasing pattern of both luminescence entities, the peak to peak amplitude of the EPR signal indicates an initial increase for the initial 16min of immersion, followed by a further decrease throughout the immersion time duration. The discontinuities monitored for both sensitivity of TL, OSL and EPR, in conjunction with the discontinuities monitored for the sensitization of TL and OSL, when plotted versus immersion time, provide an individual time scale for each one of the chemical reactions involved in the five steps of the aforementioned procedure. According to the authors' best knowledge, scarce characterization techniques could provide this time scale frame, while it is the first time that such an application of OSL and EPR is attempted. Finally, the bioactive response of the 45S5 bioglass was compared with that of the 58S sol-gel bioactive glass, in terms of the timescale of these five stages required for the final formation of the HCAp. The techniques of luminescence and EPR which take advantage of trapped charges are proposed as alternative cheap and prompt effective techniques towards discrimination between different bioactive responses in bioactive glasses.

Multicolor photoluminescence in ITQ-16 zeolite film

Exploring the native defects of zeolites is highly important for understanding the properties of zeolites, such as catalysis and optics. Here, ITQ-16 films were prepared via the secondary growth method in the presence of Ge atoms. Various intrinsic defects of ITQ-16 films were fully studied through photoluminescence and FTIR characterizations. It was found that both the as-synthesized and calcined ITQ-16 films displayed multicolor photoluminescence including ultraviolet, blue, green and red emissions by exciting upon appropriate wavelengths. The results indicate that Si―OH and non-bridging oxygen hole centers(NBOHCs) are responsible for the origin of green and red emissions at 540―800 nm, while according to a variety of emission bands of calcined ITQ-16 film, blue emission bands at around 446 and 462 nm are attributed to peroxy free radicals(≡SiO2), ultraviolet emissions ranging from 250 nm to 450 nm are suggested originating from a singlet-to-triplet transition of two-fold-coordinated Si and Ge, respectively.

Migration behavior of network-modifier cations at glass surface during electrical poling

X-ray photoelectron spectroscopy with C60-ion sputtering (C60-XPS) and electron spin resonance (ESR) revealed the migration behavior of network-modifier cations in an electrically poled soda-lime silicate glass. The Na+-deficient layer of 700-nm thickness was confirmed at the anode side surface. The Mg2+and Ca2+ existed in the 200-nm thick layer from the top surface were concentrated in the layer of 200–700nm depth from the surface. Additionally the oxygen content in the 200-nm thick layer decreased by the degassing as oxygen molecules from the glass surface, which is an essential requirement for the migration of Mg2+ and Ca2+ to cathode side. The bond scission between Si–O–Si is caused by the concentrated Mg2+ and Ca2+, resulting the formation of SiO−(Mg2+ or Ca2+)−OSi and Si· (Si E′ center). We have also confirmed the generation of oxygen hole center (NBOHC) and peroxy radical (POR) in the electrically poled soda-lime silicate glass.