Phosphorus Oxygen Hole Center Research Articles

Calibration in the Visible and Infrared Domains of Multimode Phosphosilicate Optical Fibers for Dosimetry Applications

We systematically explore the suitability of two radiation-sensitive multimode optical fibers with either P or GeP-doped cores, to serve as the sensing elements in point or distributed dosimeters. To this end, we measured the dependences of their spectral Radiation-Induced Attenuation (RIA) in the visible and near-infrared (near-IR) domain (400 - 2100 nm) up to total ionizing dose (TID) of 5 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), while varying the irradiation temperature from -80 °C to +80 °C and the dose rate between 1 mGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s and 10 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s. To assess the fiber radiation sensitivity calibration coefficients, we studied the linearity of the RIA vs TID response across our whole spectral range. Once confirmed, their “radiation sensitivity calibration” curves are obtained in the tested ranges of environmental parameters, including the dispersion related to dose rate and temperature. Both fibers present very similar curves despite their different chemical compositions. We then studied the recovery kinetics at the different temperatures of the two fibers to investigate the stability of the RIA response. Our results show that the Ge-codoping only slightly increases the IR sensitivity related to P1 defects while keeping unchanged the visible – near-IR RIA, where the contribution of phosphorus-oxygen-hole centers (POHC) is dominant. On the contrary, after the irradiation the responses of the two fibers differ, as the recovery kinetics of the GeP fiber are strongly affected by temperature, limiting its dosimetry capabilities with respect to the P fiber.

Optical spectroscopy assessment of the impact of γ-ray irradiation on Gd3+-doped phosphate glass

The effects of γ-ray irradiation (10, 100 kGy) on Gd3+-doped phosphate glass were evaluated. Glass irradiated at 100 kGy was characterized alongside the pristine by differential scanning calorimetry, Fourier transform-infrared spectroscopy and Raman scattering, wherein a lack of alteration in thermal and structural properties was supported. Yet, absorption bands developed around 500 nm with γ-ray dose indicating phosphorus oxygen hole center defects. Optical band gap and Urbach energies exhibited decreasing and increasing trends, respectively, reflecting the influence of trapped electrons and increased disorder/defects. By exciting γ-irradiated samples at 265 nm, blue radio-photoluminescence was observed where intensity increased with dose. Decay curves measured monitoring 415 nm emission showed first-order kinetics suggested to arise from phosphorus electron centers. Emission from Gd3+ was quenched with gamma-ray dose while the 6P7/2 emitting state lifetimes decreased. Correlations between Gd3+ emission intensities and lifetimes with optical band gaps suggest electron center defects perform as ‘energy sinks’.

Radiation resistance of praseodymium-doped aluminum lithium fluorophosphate scintillator glasses for laser fusion experiments

We report the gamma (γ)-ray radiation resistance of praseodymium (Pr3+)-doped aluminum lithium fluorophosphate scintillator glasses. For its assessment as a scintillator material for laser fusion experiments, a 20Al(PO3)3-80LiF-PrF3 (Pr3+-doped APLF) glass was irradiated with γ-rays from a cobalt-60 (60Co) source resulting in an absorbed dose of 5.2 kGy. Although γ-ray-irradiation results in increased absorption due to phosphorus-oxygen hole centers (POHCs) and PO3 2− electron centers (PO3 ECs), these radiation-induced defects do not modify the glass emission as both non-irradiated and γ-ray-irradiated glasses exhibit similar emission spectra and decay times under optical and X-ray excitation. The emission peaks observed also correspond to the different interconfigurational 4f5d → 4f2 and intraconfigurational 4f2 transitions of Pr3+ ions which are neither oxidized nor reduced by irradiation. Our results show that Pr3+-doped APLF glass still maintains its characteristic fast decay time and that γ-ray irradiation does not affect the glass scintillation mechanisms.

High Temperature Reverse Bias (HTRB) &amp; Temperature Humidity Bias (THB) Reliability Failure Mechanisms and Improvements in Trench Power MOSFET and IGBT

High Temperature Reverse Bias (HTRB) reliability failure is found to be caused by huge amount of undesirable hydrogen proton (H+) ions from packaging resin or external environment, while Temperature Humidity Bias (THB) reliability failure is known to be caused by moisture accumulation. A commonly known method of improving HTRB is by increasing phosphorus concentration in the PMD layer to enhance device gettering capability against H+. However, this is usually achieved at the expense of THB reliability as excessive phosphorus on the PMD surface gives rise to moisture accumulation and caused THB failure. In this paper, we performed a series of experiments to uncover two elements in PMD that are responsible to getter H+, which are Phosphorus-Oxygen-Hole-Center (POHC) and dangling bonds. We also discussed 2 possible ways to boost these H+ gettering elements to improve HTRB reliability without the adverse impact on THB reliability: Utilization of Plasma Enhanced Chemical Vapor Deposition (PECVD) Phospho-Tetraethyl-Orthosilicate (PTEOS) in PMD layer to replace the commonly used Atmospheric Pressure Chemical Vapor Deposition (APCVD) or Sub Atmospheric Chemical Vapor Deposition (SACVD) Boro-Phospho-Tetraethyl-Orthosilicate (BPTEOS) and the introduction of Tetraethyl-Orthosilicate (TEOS) capping layer on PMD layer. Both methods have proven to greatly alleviate HTRB and THB reliability marginality problems.

Defects of laser-irradiated KDP crystals with different fluences studied by photoluminescence spectroscopy

Photoluminescence (PL) bands from potassium dihydrogen phosphate (KDP) crystals are studied by time-resolved PL spectroscopy. KDP crystals irradiated at a laser fluence of 11.5 J/cm2 are found to have the highest probability of phosphorus–oxygen hole center defects and the lowest probability of phosphorus-oxygen electric center defects, in contrast to the probabilities of these defects for KDP crystals irradiated at 9.0 J/cm2. The probabilities of these two defects occurring in retired components are found to be intermediate between those for crystals irradiated at the two different fluences. The two types of defects may result from two different mechanisms and may interconvert under certain conditions. Thus, there are differences between the defects in KDP crystals irradiated at a high laser fluence and those in retired components.

Transient and Steady-State Radiation Response of Phosphosilicate Optical Fibers: Influence of H2 Loading

The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state ( $\gamma $ - and X-rays) irradiations. The influence of a H2 preloading on the fiber radiation-induced attenuation (RIA) in the 300–2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the different point defects responsible for the induced losses and their H2 dependence. All our data at room temperature (RT) highlight a strong positive impact of H2, even at very low concentrations, on the RIA. Hydrogen quickly passivates ( $t s) most of the defects responsible for the visible–near-IR RIA, mainly phosphorus oxygen hole centers (POHC) and P1 defects. However, 1 year after the H2 loading at RT or when operating at liquid nitrogen temperature, the RIA levels of the not-treated and H2-loaded fiber become comparable. The obtained results provide a better understanding of the potential and limitations of H2-loading treatment to design radiation-hardened fiber links.

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.

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.

The Effect of Electron Irradiation on the Structure of Sodium Aluminum-Iron Phosphate Glasses

ABSTRACTGlasses of the series (mol.%) 40 Na2O, (20-x) Al2O3, x Fe2O3, 40 P2O5 were irradiated with 8 MeV electrons to doses equivalent of 0.1, 0.5, and 1.0 MGy and characterized by FTIR spectroscopy and ESR at room temperature. FTIR spectra of all the glasses consist of strong bands due to O-P-O stretching modes in (PO4)3- and (P2O7)4- units at 1000-1200 cm-1, P-O-P stretching modes at 900-950 cm-1 (νas) and 700-750 cm-1 (νs), and bending modes in the PO4 units. The wavenumber range lower 800 cm-1 has some contribution due to stretching modes in MO4 and MO6 (M = Al, Fe) units. Moreover the bands at 3300-3700 cm-1 and 1550-1650 cm-1 due to stretching and bending modes in both absorbed and structurally bound H2O molecules were present. As irradiation dose increases the bands due to stretching and bending modes in water molecules and M-O-H bonds become stronger and are split. No essential changes with increasing dose were observed within the spectral range of stretching modes of the O-P-O and P-O-P bonds. Irradiation yields phosphorus-oxygen hole centers - PO42- (D5) and PO42- (D6), and PO32- ion-radicals (D2) observable in ESR spectra of low-Fe glasses. At x&gt;5 their responses are overlapped with strong broad line due to Fe(III). On the whole, with the increase in iron content the glass structural evolution decrease.

Optical, structural and thermal properties of sodium metaphosphate glasses containing Bi2O3 with interactions of gamma rays

Sodium metaphosphate glasses with successive increasing added Bi2O3 contents (5–40%) were prepared to improve their chemical stability and increase their optical and thermal properties through the additional building BiO6 and BiO3 units. The optical spectrum of the base metaphosphate glass reveals strong UV absorption due to the presence of trace iron (Fe3+) ions present as impurities. Glasses containing additional 5, 7.5 and 10% Bi2O3 show further band around 406nm which can be related to absorption of Bi3+ ions. With increasing the Bi2O3 content, this near visible band is observed to disappear indicating peculiar behavior needing further work. Gamma irradiation causes only minor changes in the position of the strong UV peaks but an obvious induced visible broad band centered at 452–460nm in the base and Bi2O3 containing glasses. This induced band is related to the generation of phosphorus oxygen hole center or non bridging oxygen hole center as revealed by various authors. FTIR results reveal characteristic vibrational bands due to phosphate groups and with the addition of Bi2O3, some interference of BiO vibrational units are expected. Gamma irradiation causes limited changes in the IR spectra due to suggested shielding effect of the heavy metal oxide Bi2O3.

Reduced radiation damage in a multicomponent phosphate glass by Nb^5+ or Sb^3+ doping

An experimental investigation on the effects of Niobium and Antimony (Nb and Sb) on the radiation response of the multicomponent phosphate glass used for higher optical gain single mode fiber has been carried out. The samples were irradiated with γ-rays up to 20 kGy. Optical absorption spectra and Electron Paramagnetic Resonance (EPR) were employed to investigate the radiation-induced-defects. We found that the radiation induced attenuation (RIA) decrease with increasing Nb5+ and Sb3+ doping concentration. Only the phosphorus oxygen hole center (POHC) related EPR signals were observed in the Nb5+-doped samples. Both POHC and phosphorus-oxygen electron centers (POEC) related EPR signals decrease obviously with 1 mol % Sb2O3 doping concentration. These experimental results were interpreted by a model that is based on competition between various defects and Nb- or Sb-ions for the holes and electrons generated by the absorption of γ-rays.

Spatially resolved measurement of high doses in microbeam radiation therapy using samarium doped fluorophosphate glasses

The measurement of spatially resolved high doses in microbeam radiation therapy has always been a challenging task, where a combination of high dose response and high spatial resolution (microns) is required for synchrotron radiation peaked around 50 keV. The x-ray induced Sm3+ → Sm2+ valence conversion in Sm3+ doped fluorophosphates glasses has been tested for use in x-ray dosimetry for microbeam radiation therapy. The conversion efficiency depends almost linearly on the dose of irradiation up to ∼5 Gy and saturates at doses exceeding ∼80 Gy. The conversion shows strong correlation with x-ray induced absorbance of the glass which is related to the formation of phosphorus-oxygen hole centers. When irradiated through a microslit collimator, a good spatial resolution and high “peak-to-valley” contrast have been observed by means of confocal photoluminescence microscopy.

Femtosecond laser writing of waveguides in zinc phosphate glasses [Invited

We have studied the relationship between the initial glass composition and the structural changes associated with laser-induced refractive index modification in a series of Er-Yb doped and undoped zinc phosphate glasses. White light microscopy and waveguide experiments are used together with Raman and fluorescence spectroscopy to characterize the structural changes. The correlation between Raman peak shifts and fluorescence from phosphorus–oxygen hole center (POHC) defects indicates that fs-laser writing results in a depolymerization of the phosphate glass network. The results also show that the exact glass composition should be taken into account when fabricating waveguide devices in phosphate glasses, in order to both expand the fs-laser processing conditions and maximize favorable morphological changes for 3-D photonic devices.

Spectroscopic studies of the origin of radiation-induced degradation in phosphorus-doped optical fibers and preforms

In this paper, we study the radiation-induced point defects related to the phosphorus element that is commonly used to improve the optical properties of silica-based glasses but is responsible of a dramatic increase in their radiation sensitivity. To this aim, the influence of x-ray irradiation on prototype phosphorus-doped canonical fibers and their related preforms was investigated by in situ radiation induced attenuation (RIA), optical absorption, and electron spin resonance (ESR) spectroscopy. The RIA spectra in the (1.5–5 eV) range, can be explained by the presence of at least three absorption bands induced by radiation exposure. Additionally the X-dose dependence of such bands was studied. The main responsible defect for these absorption peaks was the phosphorus oxygen hole center (POHC) center, whose presence was also detected by ESR measurements both in irradiated fibers and preforms, together with the lineshape of the so called P2 defect. Correlations between the RIA bands and the ESR results allow us to assign the 2.3 and 3.0 eV bands to POHCs and to propose a scheme for the simultaneous creation of POHC and P2 defects after x-ray exposure.

Gamma and UV Radiation-Induced Color Centers in Optical Fibers

Radiation-induced losses and paramagnetic centers were investigated in phosphorusdoped and P-free multimode germanosilicate optical fibers after g-rays (~1 MeV) and ultraviolet (5 eV) exposures. After both types of irradiation, the same defects seem to be responsible of the fiber absorption in the spectral range 400 to 1650 nm. In particular, the P1 centers and the Phosphorus Oxygen Hole centers are created in both cases in the phosphorus-doped fibers and explain the high permanent radiation-induced attenuation levels observed in this fiber type. Luminescence and electron spin resonance measurements (77 K, ~9.38 GHz) on irradiated samples confirm that the GeE’, SiE’ and NBOHC defects are also generated in the different irradiated samples. From this study, it seems that the pertinence of a multimode fiber for nuclear space or civil applications could be estimated through low-cost ultraviolet measurements.

Composition/Structure Relationships in Monolithic Borophosphosilicate Glasses Obtained by the Sol−Gel Route

Monolithic borophosphosilicate glasses were prepared by the sol−gel route through xerogel densification. Tetramethoxysilane (Si(OCH3)4), trimethylborate (B(OCH3)3), and trimethyl phosphite (P(OCH3)3) were used as source compounds for Si, B, and P, respectively. After drying, samples underwent thermal treatment up to 700 °C with alternating flowing oxygen and reduced pressure steps, resulting in transparent, monolithic glasses. The sample chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). Densification was investigated by vibrational spectroscopies (FT-IR, micro-Raman). The boron oxygen hole centers (BOHC) and phosphorus oxygen hole centers (POHC) paramagnetic defects generated by X-ray irradiation of glasses were studied by electron paramagnetic resonance (EPR) spectroscopy. The results obtained on borophosphosilicate glasses showed that paramagnetic defects are not created by independent processes, as expected for randomly distributed noninteracting B and P doping elements. Diamagnetic precursors of BOHC and POHC are thus proposed to be spatially close together in the glasses.

Photochemistry in phosphorus-doped silica glass by ArF excimer laser irradiation: Crucial effect of H2 loading

A striking difference in photochemistry induced by ArF excimer laser irradiation was found between H2-unloaded and H2-loaded P-doped SiO2 glasses. Although a pair of phosphorus-electron center and phosphorus-oxygen-hole center (POHC) were produced in the former, PHO2 (pyramidal shape) and PO2 (planar) centers were created instead of the POHC in the latter. The present finding strongly suggests that H2 loading treatment of P-doped SiO2 at ambient temperature induces a drastic structural alternation around phosphorus, leading to new precursor structures which account to the photosensitivity of the materials.

Infrared, Raman, and Electron Spin Resonance Studies of Vitreous Alkaline Tungsten Phosphates and Related Glasses

Ternary phosphates are found to vitrify within large domains of compositions inside the phase diagrams P2O5–WO3–A2O (A = Li, Na). Structural approach of the highly modified glasses P2O5–A2MoO4–A2O (M = Mo,W) was investigated using various spectroscopic techniques such as infrared, Raman, and electron spin resonance (ESR). These glasses were found to contain MO6octahedra, MO4tetrahedra, M2O7dimers, PO4tetrahedra, and also P2O7or metaphosphate chains, depending on the composition considered. As shown in earlier studies, the glass network is progressively depolymerized as the content of A2O increases. ESR experiments were conducted on both X‐ray irradiated and unirradiated samples. Unirradiated glasses exhibit two ESR signals attributed to W5+ and Mo5+ centers that are octahedrally coordinated. Irradiation of these glasses induces new paramagnetic centers ascribed to the phosphorus–oxygen–hole–center and peroxy radicals. The M5+ concentration depends strongly on the sample composition and temperature. ESR parameters are determined using a computer simulation approach adapted for vitreous materials.

Investigation of the medium range structure of phosphosilicate glasses by cw-EPR, 1D-ESEEM and HYSCORE spectroscopies

6Li 2O 3P 2O 5 6SiO 2 and 6Na 2O 3P 2O 5 6SiO 2 glasses were exposed to 60Co γ-ray irradiation for the production of paramagnetic states that were studied by continuous wave(cw)-EPR, 1D-electron spin echo envelop modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectroscopies. The cw-EPR signal consisted of a doublet separated by ≈47 G. This doublet was assigned to the Q n=2 -type center (POHC-defect). The analysis of the 1D-ESEEM peaks determined the A iso and T ⊥ parameters. Using the point dipole approximation for T ⊥, the r(P–O–P)-distance was estimated to be ≈2.83 and ≈3.49 Å while the P–O–P bond angle was determined to be ≈107° and ≈168° for Li and Na containing glasses, respectively. HYSCORE spectroscopy unveiled the presence of alkali metal ions in close proximity to the phosphorus oxygen hole center (POHC). The experimental findings together with SCF-HF calculations suggested the existence of the POHC–POHC–Li/Na complex (Q 2–Q 2–Li/Na-structure) in the glasses. It has been demonstrated that the advanced EPR techniques extend the spatial resolution of the cw-EPR spectroscopy to the medium range structure of the amorphous state.

EPR and UV-Raman study of BPSG thin films: structure and defects

Borophosphosilicate glass (BPSG) films produced by Sub-Atmospheric Pressure Chemical Vapor Deposition (SACVD) with different B and P concentrations have been investigated by ultra-violet (UV) Raman and electron paramagnetic resonance (EPR) spectroscopies. We observe a correlation between the main feature of the UV-Raman spectra in the as deposited films, the line at 1326(2) cm −1 attributed to the stretching vibrations of the PO double bond, and the spin resonance signals attributed to the stable phosphorus–oxygen-hole-center (POHC) created after room temperature X-ray irradiation. The intensity of the PO line as well as the intensity of the POHC EPR signal depend on the B content. The metastable configuration, POHC m , has been also observed by EPR. The B content does not affect significantly the concentration of this paramagnetic defect.