Linear and nonlinear optical properties of Tellurium Vanadate (Te2V2O9)

We report here the structure property correlation of Tellurium Vanadate (Te2V2O9) through various optical and vibrational spectroscopic investigations. Pure phase polycrystalline powder of Te2V2O9 was prepared by solid state reaction technique. Phase purity of the sample was confirmed by Powder X-Ray diffraction and the microstructural investigation was analyzed using Scanning Electron Microscopy. Raman microscopy was employed to validate the molecular structure. Diffused Reflectance and Photoluminescence spectroscopy were employed to study the optical properties. Because of non-centrosymmetry, we also observed second harmonic generation in tellurium vanadate. Subsequently, third order nonlinear optical response of Te2V2O9 was probed using open-aperture Z-scan technique estimating the nonlinear absorption coefficient to be 1e-10 mW(-1). The mechanism of nonlinear absorption was deduced to be a two-photon absorption process. This was ascertained through existence of excited states predicted from electronic structure of Te2V2O9 using Density Functional Theory. It is also noteworthy to highlight that Te2V2O9 possess higher nonlinear optical coefficient than other vanadate compounds reported in literature. (C) 2017 Elsevier B.V. All rights reserved

Investigation of nonlinear optical and photocatalytic properties of sol-gel derived KBiFe2O5

KBiFe2O5 polycrystalline powder was synthesized via citrate assisted sol-gel route. Its structural, microstructural, linear, nonlinear optical and photocatalytic properties were investigated. X-ray diffraction analysis revealed its structure to be monoclinic phase at room temperature. Nonlinear optical absorption of this material was investigated using open aperture z-scan technique. A three-photon type absorption mechanism fitted well with the experimental data, and the corresponding nonlinear absorption coefficient was calculated to be 4x10(-23)m(3)/W-2. The band gap of this material as determined by diffuse reflectance spectroscopy was found to be 1.75eV. This makes it suitable for visible light driven photocatalytic applications. The photocatalytic property of KBiFe2O5 was investigated by degradation of methylene blue under visible light irradiation at different pH. The degradation rate constant was found to be 0.031min(-1) at a pH of 11

Nonlinear optical properties of lead-free ferroelectric nanostructured perovskite

Lead-free perovskite materials with superior physical properties are currently explored for ferroelectric and optoelectronic applications. Ferroelectric materials that have large spontaneous polarization concomitantly possess large nonlinear optical response which is highly suitable for novel photonic applications. Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) is one such novel lead-free ferroelectric material with large piezoelectric response arising from existence of morphotropic phase boundary. Conventional sol-gel technique was adopted for synthesizing nanostructured BCZT (nano-BCZT) powder using citrate precursor route. X-ray powder diffraction confirmed the phase purity and high-resolution transmission electron microscopy (HRTEM) proved that the as-synthesized BCZT was indeed nanostructured. Supportively, Raman vibrational analysis was employed to validate the site occupancies of dopants and structural correlations when compared to undoped and pristine barium titanate. Nanostructured barium titanate is extensively studied as biomarkers in second harmonic generation (SHG) microscopy for bio-medical applications. In our current work, we have explored both second- and third-order nonlinear optical response of nano-BCZT. These were found to exhibit stronger SHG signal than potassium di-hydrogen phosphate (KDP) which is a well-known SHG standard. Subsequently, we also have investigated their third-order nonlinear optical properties using open aperture Z-scan technique at 532-nm excitation wavelength in the nanosecond regime. Nano-BCZT was found to exhibit strong two-photon absorption behavior. Such materials with multiphoton absorption behavior are favorable for nonlinear photonics devices such as optical limiters and contrast agents in nonlinear optical microscopy

One- and Two-Photon Absorption in CdS Nanodots and Wires: The Role of Dimensionality in the One- and Two-Photon Luminescence Excitation Spectrum

We investigate the spectral dependence of the linear and two-photon absorption of wurtzite CdS nanoparticles (dots and rods) by means of quantitative one- and two-photon photoluminescence excitation spectroscopy and effective mass theory modeling. Absolute two-photon absorption cross sections free from spectrally varying beam related uncertainties are obtained by means of a new reference dye-based method. The two-photon spectrum features of rods strongly differ from those of dots, due to the distinct energy structure of quasi-one-dimensional systems. The transversal confinement is found to dominate the energy of the absorption maxima while the longitudinal one dominates their absorption intensity. This suggests two-photon transition energy and intensity can be controlled independently in nanorods. For both geometries we observe a sizable spectral shift between the first one- and two-photon absorption maxima, which we conclude is inherent to the small rates of near-bandgap two-photon transitions rather than to the particular geometry of the absorber. The provided understanding of the spectral dependence of the two-photon absorption of CdS dots and rods is of strong interest for the design of nanocrystals with optimized two-photon absorption properties for bioimaging and phototherapy applications..A. and U.W. acknowledge funding by DFG SPP 1165 Nanowires. A.B., J.L.M., J.I.C., and J.P. acknowledge support from MICINN project CTQ-2011-27324 and UJI-BANCAIXA project P1-1B2011-01. A.P. and A.A. acknowledge partial support from ELECTRONICS 2.2.19.3 project. M.A. acknowl- edges partial support from CHEMREAGENTS 1.33 project

Impact of the COVID-19 pandemic on patients with paediatric cancer in low-income, middle-income and high-income countries: a multicentre, international, observational cohort study

OBJECTIVES: Paediatric cancer is a leading cause of death for children. Children in low-income and middle-income countries (LMICs) were four times more likely to die than children in high-income countries (HICs). This study aimed to test the hypothesis that the COVID-19 pandemic had affected the delivery of healthcare services worldwide, and exacerbated the disparity in paediatric cancer outcomes between LMICs and HICs. DESIGN: A multicentre, international, collaborative cohort study. SETTING: 91 hospitals and cancer centres in 39 countries providing cancer treatment to paediatric patients between March and December 2020. PARTICIPANTS: Patients were included if they were under the age of 18 years, and newly diagnosed with or undergoing active cancer treatment for Acute lymphoblastic leukaemia, non-Hodgkin's lymphoma, Hodgkin lymphoma, Wilms' tumour, sarcoma, retinoblastoma, gliomas, medulloblastomas or neuroblastomas, in keeping with the WHO Global Initiative for Childhood Cancer. MAIN OUTCOME MEASURE: All-cause mortality at 30 days and 90 days. RESULTS: 1660 patients were recruited. 219 children had changes to their treatment due to the pandemic. Patients in LMICs were primarily affected (n=182/219, 83.1%). Relative to patients with paediatric cancer in HICs, patients with paediatric cancer in LMICs had 12.1 (95% CI 2.93 to 50.3) and 7.9 (95% CI 3.2 to 19.7) times the odds of death at 30 days and 90 days, respectively, after presentation during the COVID-19 pandemic (p<0.001). After adjusting for confounders, patients with paediatric cancer in LMICs had 15.6 (95% CI 3.7 to 65.8) times the odds of death at 30 days (p<0.001). CONCLUSIONS: The COVID-19 pandemic has affected paediatric oncology service provision. It has disproportionately affected patients in LMICs, highlighting and compounding existing disparities in healthcare systems globally that need addressing urgently. However, many patients with paediatric cancer continued to receive their normal standard of care. This speaks to the adaptability and resilience of healthcare systems and healthcare workers globally