Center Defects Research Articles

Multiphoton-Absorption-Excited Up-Conversion Luminescence in Optical Fibers

We experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation.

FandMcenters in alkali halides: A theoretical study applying self-consistent dielectric-dependent hybrid density functional theory

Point defects significantly change electronic properties of alkali halides and thereby enhance their reactivity. However, both the experimental and theoretical description of defects such as the $F$ center and the $M$ center are still far from complete, in particular for the less common bromides. A self-consistent dielectric-dependent global hybrid and plane-wave approach is employed for a comparative theoretical study of the electronic properties of NaCl, KCl, NaBr, and KBr bulk and (100) surface, both perfect and defective. For these systems, a zero-point renormalization was calculated to account for electron-phonon interaction and enhance comparability with the experiment. We focus on anion vacancy defects, the so-called $F$ and $M$ centers. The methodology employed is capable of reproducing measured defect level energies, electronic band gaps, ionization energies, and electron affinities within experimental errors. A general trend of the $F$ center defect level energy with respect to the lattice parameter is found. The results for both the $F$ and the $M$ center of KCl agree with findings from magnetic resonance experiments. The defect orbitals are analyzed and virtual states of the defect electron are identified.

Influence of multi-energy boron difluoride implantation on the second-harmonic generation of thermally poled fused silica

Abstract Multi-energy (10–50 keV) boron difluoride (49BF2+) ions are implanted at a dose of 1015 cm−2 in the fused silica substrate to form a thin layer structure with a thickness of about 120 nm. The refractive index of fused silica substrate increases as a result of BF2 implantation, which applies to optical waveguide fabrication. Moreover, the absorption spectrum of the implanted sample shows two absorption peaks in the photon energy range from 4.0 eV to 6.52 eV, which are likely resulted from the B2β, oxygen divacancy and surface E′ center defects. The sample is thermally poled at the conditions of 5 kV, 60 min, and different temperatures, and the second-harmonic (SH) signal is measured using the Maker fringe technique. At low and moderate poling temperatures, the implanted and non-implanted samples have the same trend of SH signal variation with poling temperature (both increases first, and then reaches a maximum saturation value), and these signals have equivalent strength. At high poling temperature, the SH signal of the implanted sample is enhanced continuously, but the SH signal of the non-implanted sample is attenuated. The charge migration model of mobile ions can qualitatively explain the generation mechanism for second-order optical nonlinearity (SON) of the poled sample. The multi-energy BF2 ion implantation is found, for the first time, that it can enhance about 1.7 times of the SH signal of thermally poled fused silica glass at a high poling temperature.

CW EPR Investigation of Red‐Emitting CaS:Eu Phosphors: Rationalization of Local Electronic Structure

AbstractA series of commercial and prepared CaS:Eu2+ rare earth activated phosphors are investigated following different post‐synthetic treatments. A number of species directly related to the function of the material are characterized using electron paramagnetic resonance (EPR) spectroscopy. Isolated Eu2+ sites are identified and associated with the substitutional doping for Ca2+ in the lattice which are responsible for the 645 nm emission of interest. Another inactive Eu2+ site based within a “EuO” type phase aggregated on the surface of the material is also identified, as well as competitive F+ center defects that are known to reduce emission from the Eu2+ sites. Intrinsic Mn2+ impurities are identified and used as local order probes to determine changes in ordering and symmetry upon cryo‐milling and heating treatments of the samples. X‐ray photoelectron (XPS) and photoluminescence (PL) spectroscopies are also conducted to complement the local structure observations. The reported data is useful in understanding how the nature of the lattice affects ground state electronic structure of functional defective sites, for the development of efficient and selective materials.

Exact analysis of mode-III cohesive fracture in layered elastic composites

This paper examines the mechanics of mode-III defect initiation and quasi-static growth in a composite consisting of N layers separated by nonuniform nonlinear cohesive surfaces. The exact analysis is based on the elasticity solution to the problem of a single layer of finite width and thickness subjected to arbitrary, nonuniform but equilibrated shear tractions on top and bottom surfaces. The formulation leads to a system of integral equations governing rigid body layer translations and cohesive surface slip fields (tangential jump discontinuities across layer interfaces). Cohesive surfaces are modelled by traction-slip relations (exponential, modified exponential) characterized by a cohesive strength, a force length and possibly friction parameters. Symmetric center, edge and array defects are modeled by cohesive strength functions that vary with surface coordinate. Infinitesimal strain equilibrium solutions are sought by eigenfunction approximation of the solution of the governing integral equations. Solutions indicate that quasi-static defect initiation/propagation occur under increasing applied shear traction. For small values of force length, brittle behavior occurs corresponding to sharp crack growth. At larger values of force length, ductile response occurs similar to linear “spring” cohesive surfaces. Both behaviors ultimately cause abrupt failure of the surface. Results for the stiff, strong cohesive surface with a center defect under a small applied traction agree well with static crack solutions taken from the literature. Detailed results are obtained for (i) an array of symmetric collinear defects accounting for defect–defect interaction, (ii) a symmetric defect in a bilayer with nonuniform material properties/thicknesses, (iii) a center defect accounting for decohesion and friction.

Broadband Optical Detection of Ferromagnetic Resonance From the Organic-Based Ferrimagnet V[TCNE] x Using N- V Centers in Diamond

Nitrogen-vacancy (N-V) center defects in diamond enable local, optical detection of magnons, owing to their sensitivity to gigahertz frequency magnetic field noise. Applied to ferromagnetic dynamics sensing, N-Vs can be used to sense an increase in the population of N-V-resonant magnons in a nearby ferromagnetic film, which arise from microwave drive of the uniform-mode ferromagnetic resonance and the subsequent scattering of uniform-mode magnon population throughout the magnon states. In this work we utilize N-V sensing to detect ferromagnetic resonance in films of the low magnetization, ferrimagnetic, coordination compound vanadium tetracyanoethylene (V$[\mathrm{TCNE}{]}_{x}$). From an applications standpoint V$[\mathrm{TCNE}{]}_{x}$ has excellent magnetic resonance properties rivalling the best magnetic oxides and it can be deposited on a wide range of substrates, unlike most oxides. The remarkably low magnetization of V$[\mathrm{TCNE}{]}_{x}$ offers the chance to probe N-V-ferromagnet coupling in a yet-unexplored regime. We simultaneously detect broadband FMR spectroscopy of V$[\mathrm{TCNE}{]}_{x}$ films by both conventional microwave absorption and N-V techniques, finding few-gauss magnetic resonance linewidth and a magnetization of 49 G by both methods. Using spin-wave theory, we calculate the N-V-resonant spin-wave wavelengths to be on the order of tens of nanometers, with wavevectors on the order of ${10}^{8}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$. Our measurements highlight that the low magnetization of V$[\mathrm{TNCE}{]}_{x}$ results in very short wavelength spin waves at few-GHz frequencies, which can have significant advantage for future nanoscale magnonic applications.

Dietary Management for Adolescents with Prader-Willi Syndrome.

Prader–Willi syndrome (PWS) is a complex, multisystem neurodevelopmental disorder affecting approximately 1 in 25,000 live births. PWS is caused by absence of expression of paternally inherited imprinted genes on chromosome 15q11-q13. The syndrome typically occurs due to one of three genetic mechanisms: paternal deletion of involved genes, maternal uniparental disomy, or imprinting center defects. These genetic anomalies lead to well-described clinical phenotype that includes hypotonia, hypothalamic dysfunction, social and behavioral issues, life-threatening hyperphagia, and elevated probability of obesity. Adolescents with PWS are at the highest risk for development of life-threatening obesity due to increased access to food, decreased physical activity, and hyperphagia. Currently, the only treatment for the hyperphagia is environmental control, including locked kitchens and continuous supervision of the affected individual. Caloric intake must be restricted to prevent obesity, which subsequently increases the hunger drive even more. Research and clinical practice have demonstrated that increasing physical activity along with insuring a well-balanced, nutritionally dense diet can improve overall weight control in adolescents with PWS.

A New Technique for Analyzing Defects in Silicon Carbide Devices: Electrically Detected Electron Nuclear Double Resonance

We show that electrically detected electron nuclear double resonance (EDENDOR) can be detected with relatively high signal-to-noise ratios in fully processed 4H-SiC bipolar junction transistors (BJTs). We observe EDENDOR of nitrogen interacting with recombination center defects in the depletion region of forward-biased emitter-base junctions of these devices at room temperature. Our results indicate that EDENDOR has great potential in the investigation of SiC-based devices specifically, as well as in the investigation of solid-state devices based upon other material systems.

Thermal transport and optical spectroscopy in 710-MeV Bi ion irradiated LiF crystals

We present thermal conductivity measurements of lithium fluoride single crystals irradiated by 710 MeV Bi ions at fluences ranging between 1010 and 1013 cm−2. The thermal transport degradation due to irradiation damage was examined across two depths regions, on nanometer and micrometer scales, by picosecond time-domain thermoreflectance and modulated continuum wave thermoreflectance methods, respectively. The proliferation of swift heavy ion-induced structural defects (color centers) was characterized using optical absorption and photoluminescence spectroscopies. Klemens thermal model was applied to correlate the concentrations of color center defects to thermal conductivity reduction in irradiated LiF crystals.

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.

Histocompatibility Complex Status and Mendelian Randomization Analysis in Unsolved Antibody Deficiency.

The pathogenesis in the majority of patients with common variable immunodeficiency (CVID), the most common symptomatic primary immunodeficiency, remains unknown. We aimed to compare the minor and major histocompatibility complex (MHC) markers as well as polygenic scores of common genetic variants between patients with monogenic CVID and without known genetic mutation detected. Monogenic patients were identified in a CVID cohort using whole exome sequencing. Computational full-resolution MHC typing and confirmatory PCR amplicon-based high-resolution typing were performed. Exome-wide polygenic scores were developed using significantly different variants and multi-variant Mendelian randomization (MR) analyses were used to test the causality of significant genetic variants on antibody levels and susceptibility to infectious diseases. Among 83 CVID patients (44.5% females), monogenic defects were found in 40 individuals. Evaluation of the remaining CVID patients without known genetic mutation detected showed 13 and 27 significantly associated MHC-class I and II alleles, respectively. The most significant partial haplotype linked with the unsolved CVID was W*01:01:01-DMA*01:01:01-DMB*01:03:01:02-TAP1*01:01:01 (P < 0.001), where carriers had a late onset of the disease, only infection clinical phenotype, a non-familial form of CVID, post-germinal center defects and a non-progressive form of their disease. Exclusion of monogenic diseases allowed MR analyses to identify significant genetic variants associated with bacterial infections and improved discrepancies observed in MR analyses of previous GWAS studies with low pleiotropy mainly for a lower respiratory infection, bacterial infection and Streptococcal infection. This is the first study on the full-resolution of minor and major MHC typing and polygenic scores on CVID patients and showed that exclusion of monogenic forms of the disease unraveled an independent role of MHC genes and common genetic variants in the pathogenesis of CVID.

Structural and electronic properties of β-NaYF4 and β-NaYF4:Ce3+

In this work, the density functional theory approach with linear combination of atomic orbitals (LCAO) as implemented in the CRYSTAL17 computer code is applied to hexagonal β-NaYF4, located in three possible space groups of this compound: P6‾, P63/m and P6‾2 m. First, the disordered crystalline structure of NaYF4 was modelled in a large supercell containing 108 atoms. In order to obtain better agreement with the experimental data, we used several different exchange-correlation functionals. Basic properties, such as lattice constant, band gap and total energies were calculated and compared for all three space groups and three exchange-correlation functionals - HSE06, PWGGA and PWGGA+13%HF. It was found that for all three functionals, the minimum of total energy corresponds to P6‾ space group. Secondly, in order to study the effects associated with the Ce3+ impurity and the F center (radiation defect), the P6‾ β-NaYF4 structure with the F center and Ce3+ or with both was carefully modelled. Taking into account that fluorine atoms have different nearest neighbours, several types of fluorine vacancies were simulated and an appropriate formation energies were determined. Finally, the effects of Ce3+ ion substitution of Y ions in different positions as well as formation of Ce3+, the F center defect pairs were also studied and an appropriate incorporation energies were calculated.

A placebo-controlled trial of folic acid and betaine in identical twins with Angelman syndrome

BackgroundAngelman syndrome (AS) is a neurodevelopmental disorder that is caused by maternal genetic deficiency of a gene that encodes E6-AP ubiquitin-protein ligase (gene symbol UBE3A) mapping to chromosome 15q11-q13. AS leads to stiff and jerky gait, excess laughter, seizures, and severe intellectual disability. In some parts of the brain, the paternally inherited UBE3A gene is subject to genomic imprinting by the action of the UBE3A-antisense transcript (UBE3A-ATS) on the paternally inherited allele. Consequently, only the maternally inherited UBE3A gene is expressed in mature neurons. AS occurs due to deletions of the maternal 15q11 − 13 region, paternal uniparental disomy (UPD), imprinting center defects, mutations in the maternal UBE3A gene, or other unknown genetic malfunctions that result in a silenced maternal UBE3A gene in the specific imprinted regions of the brain.ResultsA potential treatment strategy for AS is to increase methylation of UBE3A-ATS to promote expression of the paternal UBE3A gene and thus ameliorate the clinical phenotypes of AS. We treated two sets of male identical twins with class I deletions with a 1 year treatment trial of either betaine and folic acid versus placebo. We found no statistically significant changes in the clinical parameters tested at the end of the 1 year trial, nor did we find any significant adverse events.ConclusionsThis study tested the hypothesis that by increasing the methylation of the UBE3A-antisense transcript in Angelman syndrome to promote expression of the silenced paternal UBE3A gene we may ameliorate the clinical phenotypes of AS. We treated two sets of identical twins with placebo versus betaine and folic acid. Although this study represented a novel approach to treating Angelman syndrome, the differences in the developmental testing results was not significant. This paper also discusses the value of monozygotic twin studies in minimizing confounding variables and its utility in conducting small treatment studies.Trial registrationNCT00348933. Registered 6 July 2006.

The study of oxygen-deficient centers in Al-doped amorphous germanium oxides

Electronic and optical properties of Germanium oxygen-deficient center (GeODC) defect and Al-doped GeODC defect in 96 atoms amorphous GeO2 (a-GeO2) supercells have been investigated. All the 64 oxygen sites in the a-GeO2 configuration have been orchestrated as possible candidates for the construction of 64 different GeODCs. A Ge atom has been substituted by an Al atom in GeODCs to form the Al-GeODCs. It is discovered that the refractive index of a-GeO2 is reduced by GeODC defect, contrary to the situation when Al is doped in GeODC defect. The absorption peak at 5.15 eV is related to GeODC defect. After Al-doping, a new defect state is generated near the top of valence band (TVB), resulting in an absorption peak at 4 eV. The variations of refractive index and optical properties exhibited offer a significant and profound guidance of Al and Ge co-doping in silica optical fiber.

Sleep-Related Breathing Disorders in Young Adults With Prader-Willi Syndrome: A Placebo-Controlled, Crossover GH Trial.

Sleep-related breathing disorders (SRBD) are common in people with Prader-Willi syndrome (PWS). Young adults with PWS benefit from GH continuation after attaining adult height by maintaining the improved body composition obtained during childhood. There are, no studies about the effects of GH on SRBD in young adults with PWS who were treated with GH during childhood. Investigate the effects of GH vs placebo on SRBD in young adults with PWS who were treated with GH during childhood and had attained adult height. Two-year, randomized, double-blind, placebo-controlled, crossover study in 27 young adults with PWS, stratified for sex and body mass index. Dutch PWS Reference Center. Crossover intervention with GH (0.67 mg/m2/d) and placebo, both over one year. Apnea hypopnea index (AHI), obstructive apnea index (OAI), central apnea index (CAI), measured by polysomnography. Compared with placebo, GH did not increase AHI, CAI, or OAI (P > 0.35). The effect of GH vs placebo was neither different between men and women, nor between patients with a deletion or maternal uniparental disomy/imprinting center defect. After two years, there was no difference in AHI, CAI, or OAI compared with baseline (P > 0.18). Two patients (7%) fulfilled the criteria of obstructive sleep apnea regardless of GH or placebo. GH compared with placebo does not cause a substantial increase in AHI, CAI, or OAI in adults with PWS who were treated with GH during childhood and have attained adult height. Our findings are reassuring and prove that GH can be administered safely.

SAT-380 Screening for Central Adrenal Insufficiency in Children with Prader-Willi Syndrome (PWS) with Single Collection Of ACTH and Cortisol Levels

Baseline a.m ACTH and Cortisol levels in Children with Prader-Willi-syndrome are no different from general population. Moris Angulo, MD1 & Mariano Castro-Magaña, MD1 1Dept of Peds, NYU-Winthrop Hospital, New York, NY Background Prader-Willi syndrome (PWS) is a multi-system genetic disorder resulting from the lack of expression of the paternal genes from chromosome 15q11.2-q13 due to paternal deletion, uniparental disomy (UPD) or an imprinting center defect. Many of their features are explained by hypothalamic dysfunction, therefore individuals with PWS are at high risk for pituitary hormonal deficiency. When the pituitary begins to fail, there is generally a specific sequential failure of pituitary hormones, starting with GH, continuing through LH and FSH deficiency, and culminating in loss of TSH and ACTH. Generally, ACTH is the last to be lost. A high prevalence (60%) of central adrenal insufficiency (CAI) however, has been reported in Prader-Willi syndrome (PWS) using the metyrapone test. Many children, including infants have undergone stimulation testing to confirm or rule out CAI. Several studies however, using same test and other different testing methods including insulin tolerance test (ITT), low dose/high dose ACTH stimulation, glucagon stimulation tests have reported differing results with prevalence between 0 to 7·5%. Previous study has shown that basal cortisol is closely correlated with adrenal response to stimulation. Methods: We studied 105 children with genetic diagnosis of PWS, age 2 to__years. (60 males and 45 females) after basal Cortisol and ACTH level collected at 0800 h. Sixty eight children (60 %) had deletion I and II, 24 (23%)UPD and 13 had only positive DNA Methylation testing . All participant were already on GH treatment without illness or any other stressful condition during testing. Results: All had normal morning Cortisol and ACTH level but 2 children, age 2 and 5 years with low and 4 y.o. male with increased cortisol level. These 3 children had normal ACTH level. Repeat sample after a week, revealed normal both Cortisol and ACTH level. Conclusion: suggesting that clinically significant adrenal insufficiency in PWS is rare

Photoelectrical imaging and coherent spin-state readout of single nitrogen-vacancy centers in diamond.

Nitrogen-vacancy (NV) centers in diamond have become an important instrument for quantum sensing and quantum information science. However, the readout of NV spin state requires bulky optical setups, limiting fabrication of miniaturized compact devices for practical use. Here we realized photoelectrical detection of magnetic resonance as well as Rabi oscillations on a single-defect level. Furthermore, photoelectrical imaging of individual NV centers at room temperature was demonstrated, surpassing conventional optical readout methods by providing high imaging contrast and signal-to-noise ratio. These results pave the way toward fully integrated quantum diamond devices.

An integrated route to quantum detection

Quantum Optics The quantum properties of the nitrogen-vacancy (NV) center defect in diamond are being pursued as building blocks for quantum-enhanced technologies. Addressing and manipulating the defects, however, typically requires bulk optics, which could limit scalability. Siyushev et al. developed an on-chip technique in which the NV center is detected optoelectronically. Such a detection and manipulation method offers a route to develop an integrated platform for scalable quantum-based sensing technologies. Science , this issue p. [728][1] [1]: /lookup/doi/10.1126/science.aav2789

Impact of heat treatment on NBOHC luminescence of OH-containing and H2-impregnated fused silica for deep-ultraviolet applications

OH-containing and H2-impregnated fused silica is the optical materials of choice for deep-ultraviolet (DUV) applications. Intrinsic and UV laser irradiation induced non-bridging oxygen hole center (NBOHC) defects play a central role in the optical properties of fused silica in the DUV spectra range. Understanding the NBOHC generation mechanism is of great importance to the performance improvement. In this paper, NBOHC-related 650 nm photoluminescence (PL) band is investigated in details by heat-treating the fused silica at different temperature and exciting the PL band at different wavelength. From the 650 nm PL characteristics of un-treated and heat-treated fused silica samples excited at 193 nm, 266 nm, 355 nm, and 532 nm, it is found that the 650 nm PL band of un-treated fused silica is excited at 193 nm and 266 nm mainly via a two-photon process, and cannot be excited with 355 nm and 532 nm. The un-treated fused silica also presented a reversible time delay (annealing) in 650 nm PL intensity following an abrupt change of excitation fluence at 193 nm, due to the recombination of NBOHCs with impregnated H2. On the other hand, for the heat-treated fused silica, the 650 nm PL band is excited by a combination of one- and two-photon processes at 193 nm and 266 nm with the one-photon process dominating, and by the one-photon excitation process at 355 nm and 532 nm. The quantum yield of 650 nm PL band decreases with the decreasing excitation photon energy. From these experimental results it is confirmed with no doubt that in un-treated fused silica NBOHCs are produced by 193 nm and 266 nm laser irradiation induced photolysis of an Si‒OH group via a two-photon process, with a minimum photolysis energy between 7.0 eV and 7.9 eV. In heat-treated fused silica NBOHCs are produced by heat treatment induced breakage of Si‒OH bonds. Heat treatment also removed totally the impregnated H2 in fused silica, that makes the heat-treatment produced NBOHCs become stable and show one-photon excited 650 nm PL band when excited at 193 nm, 266 nm, 355 nm, and 532 nm. In contrary to the un-treated fused silica, the heat-treated fused silica presented no reversible time delay in 650 nm PL intensity following the abrupt change of excitation fluence at 193 nm, due to the total removal of H2 in fused silica and the absence of recombination of NBOHCs with H2.

1/f flux noise in low- Tc SQUIDs due to superparamagnetic phase transitions in defect clusters

It is shown here that $1/f^\alpha$ flux noise in conventional low-T$_c$ SQUIDs is a result of low temperature superparamagnetic phase transitions in small clusters of strongly correlated color center defects. The spins in each cluster interact via long-range ferromagnetic interactions. Due to its small size, the cluster behaves like a 'random-telegraphic' macro-spin when transitioning to the superparamagnetic phase. This results in $1/f^{\alpha}$ noise when ensemble averaged over a random distribution of clusters. This model is self-consistent and explains all related experimental results which includes $\alpha\sim 0.8$ independent of system-size. The experimental flux-inductance-noise spectrum is explained through three-point correlation calculations and time reversal symmetry breaking arguments. Also, unlike the flux noise, it is shown why the second-spectrum inductance noise is inherently temperature dependent due to the fluctuation-dissipation theorem. A correlation-function calculation methodology using Ising-Glauber dynamics was key for obtaining these results.