Photometric Characterizations Research Articles

Optically Transparent Honeycomb Mesh Antenna Integrated into OLED Light Source

The co-integration of antennas with lighting sources appears as an effective way to distribute broadband networks closer to users, lowering interference and transmitted power, as well as to reduce energy consumption in future lighting systems. We here present an original contribution to the implementation of transparent and invisible antennas with OLED light sources. To validate the proposed approach, the honeycomb mesh technique was used, and an optical transparency of 75.4% was reached. The transparent mesh antenna was compared with the non-transparent full-metal antenna in terms of radio-electrical parameters. Our prototype was designed using copper films deposited on a glass substrate. The simulation results of the S-parameters and the radiation patterns were validated against measurements performed in an anechoic chamber. The directivity and gain obtained were 6.67 dBi and 4.86 dBi at 5.16GHz, respectively. To study the effect of antenna integration with OLEDs, optical and photometric characterizations with and without the antenna were measured, and the colorimetric parameters were then treated using the IES TM-30-18 standard.

Photoluminescent investigation of Ba2LaV3O11:Dy3+ nanophosphors with cool white light emission for near-UV based WLEDs

Dy3+ doped Ba2LaV3O11 nanophosphor is one of the most promising energy converters for solid-state lighting (SSL) as it has outstanding potential to absorb near-ultraviolet light along with brilliant luminous features. Ba2LaV3O11 nanophosphors doped with varied compositions of Dy3+ ions are successfully prepared through an energy-efficient urea-based solution combustion production route. Benefitting from its facile synthesis route at low cost, longer operational lifetime the prepared nanophosphors may be used as luminescent material for WLEDs. Recently, modern white light-emitting diodes (WLEDs) have been fabricated based on the energy-conversion via efficient phosphor material. The current report is about the realization of white light emanation through doping a single dopant ion in vanadate host lattice. The outcomes evidence that the optimum Ba2La0.97Dy0.03V3O11 nanophosphor exhibits excellent performance in WLEDs. The diffuse reflectance spectrum (DRS) measured for the optimum nanopowder sample is subjected to Tauc's plot analysis, revealing a higher optical band-gap of 3.69 eV. The typical photoluminescence emission transitions of Dy3+ ions noticed in wavelength ranging from 400 nm to 650 nm are owing to intra 4f shifts upon excitation via 352 nm wavelength. In last, photometric characterizations are carried out disposing the outstanding result of color chromaticity coordinates as well as correlated color temperature (CCT) value.

Superheavy Elements in Kilonovae

As LIGO-Virgo-KAGRA enters its fourth observing run, a new opportunity to search for electromagnetic counterparts of compact object mergers will also begin. The light curves and spectra from the first “kilonova” associated with a binary neutron star merger (NSM) suggests that these sites are hosts of the rapid neutron capture (“r”) process. However, it is unknown just how robust elemental production can be in mergers. Identifying signposts of the production of particular nuclei is critical for fully understanding merger-driven heavy-element synthesis. In this study, we investigate the properties of very neutron-rich nuclei for which superheavy elements (Z ≥ 104) can be produced in NSMs and whether they can similarly imprint a unique signature on kilonova light-curve evolution. A superheavy-element signature in kilonovae represents a route to establishing a lower limit on heavy-element production in NSMs as well as possibly being the first evidence of superheavy-element synthesis in nature. Favorable NSM conditions yield a mass fraction of superheavy elements X Z≥104 ≈ 3 × 10−2 at 7.5 hr post-merger. With this mass fraction of superheavy elements, we find that the component of kilonova light curves possibly containing superheavy elements may appear similar to those arising from lanthanide-poor ejecta. Therefore, photometric characterizations of superheavy-element rich kilonova may possibly misidentify them as lanthanide-poor events.

Luminescence dynamics of Eu3+ activated and co-activated defect spinel zinc titanate nanophosphor for applications in WLEDs

The luminescence properties of novel Eu3+ doped and (Li+,Ni2+) co-doped ZnTiO3 nanophosphors were reported in this work. The powder samples were fabricated via the facile solution combustion technique. The structural and photoluminescence characteristics of ZnTiO3:0.0075Eu3+ nanophosphor are influenced by calcination temperature and co-doped ions. Under the excitation by near UV and blue light, the red luminescence of prepared nanophosphor appeared owing to strong absorption and efficient energy transfer mechanism. In the developed nanophosphors, the enhancement red emission is only possible in the presence of Li+ and Ni2+ ions. Phase transformation in high temperature form of zinc titanate improves the non-radiative transition and co-dopant ions in phase pure defect spinel can increase the rate of radiative transition. The photometric characterizations hint that the nanophosphor materials proved to be highly beneficial for the red light emission in WLEDs applications.

PACO ASDI: an algorithm for exoplanet detection and characterization in direct imaging with integral field spectrographs

Context.Exoplanet detection and characterization by direct imaging both rely on sophisticated instruments (adaptive optics and coronagraph) and adequate data processing methods. Angular and spectral differential imaging (ASDI) combines observations at different times and a range of wavelengths in order to separate the residual signal from the host star and the signal of interest corresponding to off-axis sources.Aims.Very high contrast detection is only possible with an accurate modeling of those two components, in particular of the background due to stellar leakages of the host star masked out by the coronagraph. Beyond the detection of point-like sources in the field of view, it is also essential to characterize the detection in terms of statistical significance and astrometry and to estimate the source spectrum.Methods.We extend our recent methodPACO, based on local learning of patch covariances, in order to capture the spectral and temporal fluctuations of background structures. From this statistical modeling, we build a detection algorithm and a spectrum estimation method:PACO ASDI. The modeling of spectral correlations proves useful both in reducing detection artifacts and obtaining accurate statistical guarantees (detection thresholds and photometry confidence intervals).Results.An analysis of several ASDI datasets from the VLT/SPHERE-IFS instrument shows thatPACO ASDIproduces very clean detection maps, for which setting a detection threshold is statistically reliable. Compared to other algorithms used routinely to exploit the scientific results of SPHERE-IFS, sensitivity is improved and many false detections can be avoided. Spectrally smoothed spectra are also produced byPACO ASDI. The analysis of datasets with injected fake planets validates the recovered spectra and the computed confidence intervals.Conclusions.PACO ASDIis a high-contrast processing algorithm accounting for the spatio-spectral correlations of the data to produce statistically-grounded detection maps and reliable spectral estimations. Point source detections, photometric and astrometric characterizations are fully automatized.

Kepler Planet Occurrence Rates for Mid-type M Dwarfs as a Function of Spectral Type

Abstract Previous studies of planet occurrence rates largely relied on photometric stellar characterizations. In this paper, we present planet occurrence rates for mid-type M dwarfs using spectroscopy, parallaxes, and photometry to determine stellar characteristics. Our spectroscopic observations have allowed us to constrain spectral type, temperatures, and, in some cases, metallicities for 337 out of 561 probable mid-type M dwarfs in the primary Kepler field. We use a random forest classifier to assign a spectral type to the remaining 224 stars. Combining our data with Gaia parallaxes, we compute precise (∼3%) stellar radii and masses, which we use to update planet parameters and occurrence rates for Kepler mid-type M dwarfs. Within the Kepler field, there are seven M3 V to M5 V stars that host 13 confirmed planets between 0.5 and 2.5 Earth radii and at orbital periods between 0.5 and 10 days. For this population, we compute a planet occurrence rate of planets per star. For M3 V, M4 V, and M5 V, we compute planet occurrence rates of , , and planets per star, respectively.

Sonochemical synthesis of green emitting Ca2SiO4:Er3+ nanopowders: Promising applications in optical thermometry and radiation dosimeter

The Er3+-activated Ca2SiO4 nanopowders were fabricated via sonochemical method using Epigallocatechin gallate as a bio-surfactant. The X-ray diffraction results reveal that the prepared nanopowders consist of a single phase monoclinic structure. The energy band gap of the prepared samples was estimated and found in the range 4.95–5.18 eV. The photoluminescence emission spectra exhibit intense peaks centered at ∼517, 551, 613 and 662 nm, which were attributed to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 and 4F9/2(1) → 4I15/2 transitions of Er3+ ions, respectively. The photoluminescence emission intensity increases up to 5 mol % of Er3+ concentration and later diminishes. The decrement of emission intensity with increasing Er3+ concentration was related to a self-quenching of the concentration. The cause behind the concentration quenching was proposed as a dipole–dipole interaction among Er3+ ions. Photometric characterizations of Er3+-doped Ca2SiO4 nanopowders exhibit green light emission with high color purity indicates the present nanopowders were quite useful in the fabrication of cool light emitting diodes. The sensor sensitivity of the Ca2SiO4:Er3+ (5 mol %) nanopowders was found to be ∼0.0624 K−1 at lower temperature 303 K, suggesting suitability for the optical thermometry application. Further, thermoluminescence properties of the prepared samples were extensively investigated. The activation energy and frequency factor of the prepared nanopowders were estimated and obtained values were good agreement with standard thermoluminescence materials, which specify the suitability of the prepared nanopowders in dosimetry applications. The aforementioned results confirm the synthesized nanopowders exhibit excellent photometric, sensor sensitivity and thermoluminescence properties signifying suitability in solid state lighting, optical thermometry and dosimetry applications.

Characteristic white light emission via down-conversion SrGdAlO4:Dy3+ nanophosphor

An efficient and cost-effective technique, solution combustion synthesis was used to synthesize Dy3+ doped SrGdAlO4 nanophosphor utilizing urea as a suitable fuel. The tetragonal phase and nano-crystallinity of the synthesized phosphor belonging to I4/mmm space group was confirmed by powder X-ray diffraction (PXRD) and transmission electron microscope (TEM) technique respectively. Various crystal structure parameters and refined atomic positions of host matrix and SrGd0.95Dy0.05AlO4 nanophosphor were determined by Rietveld refinement. The two intense bands i.e. blue and yellow bands were observed in photoluminescence emission spectrum recorded at 352 nm excitation wavelength, associated to transitions 4F9/2 → 6H15/2 (484 nm) and 4F9/2 → 6H13/2 (575 nm) respectively. Photometric characterizations revealed the emission of white color by the synthesized nanophosphor proving its wide applications in WLEDs (white light emitting diodes). Band gap values calculated using diffuse reflectance spectra (DRS) were found to vary in the range of 5.50 eV–5.59 eV for host and doped lattice system. Keeping in mind, the concentration quenching phenomenon, SrGd0.95Dy0.05AlO4 was considered as optimized nanophosphor for WLEDs.

Photometric and Electrical Characterizations of Large-Area OLEDs Aged Under Thermal and Electrical Stresses

The aim of this paper is to identify the electrical signatures of degradations of large-area organic light-emitting diodes (OLEDs) (41 cm² active area), subjected to various stress conditions. Three Philips GL55 OLEDs were stressed under three distinct temperature values: 23 °C, 40 °C, and 60 °C at a stress current density of J = 15 mA/cm² (rated current density: Jn = 9.49 mA/cm²). Under thermal and electrical stresses, an increase of the operating voltage was observed with stress time but thermal stress alone did neither affect the operating voltage nor the luminance values up to 60 °C.

Enhanced photoluminescence properties of electrospun Dy3+ -doped ZnO nanofibres for white lighting devices.

Dy3+ -doped ZnO nanofibres with diameters from 200 to 500nm were made using an electrospinning technique. The as-fabricated amorphous nanofibres resulted in good crystalline continuous nanofibres through calcination. Dy3+ -doped ZnO nanofibres were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) light spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL). XRD showed the well defined peaks of ZnO. UV-vis spectra showed a good absorption band at 360nm. FTIR spectra showed a Zn-O stretching vibration confirming the presence of ZnO. Photoluminescence spectra of Dy3+ -doped ZnO nanofibres showed an emission peak in the visible region that was free from any ZnO defect emission. Emissions at 480nm and 575nm in the Dy3+ -doped ZnO nanofibres were the characteristic peaks of dopant Dy3+ and implied efficient energy transfer from host to dopant. Luminescence intensity was found to be increased with increasing doping concentration and reduction in nanofibre diameter. Colour coordinates were calculated from photometric characterizations, which resembled the properties for warm white lighting devices.

Er3+-Yb3+/Er3+-Yb3+-Li+/Er3+-Yb3+-Zn2+:Gd2O3 nanophosphors for efficient frequency upconverter and temperature sensing applications

Er3+/Yb3+/Li+/Zn2+:Gd2O3 nanophosphors synthesized via combustion synthesis method have been structurally and optically characterized. The average particles size of the developed nanophosphors has been found to be ∼ 25 nm by Transmission Electron Microscopy (TEM) analysis which is in good agreement with the X-rays Diffraction (XRD) results. The significant enhancement in upconversion (UC) emission intensity for green (∼ 20 and 70 times) and red (∼ 7 and 20 times) band have been observed after codoping with Li+ and Zn2+ ions respectively in Er3+-Yb3+:Gd2O3 system. The temperature sensing capability of the optimized nanophosphors has been studied corresponding to two thermally coupled 2H11/2 and 4S3/2 levels of the Er3+ ions. The sensitivity ∼ 0.0096 K-1, 0.00109 K-1 and 0.0116 K-1 have been reported in the Er3+-Yb3+:Gd2O3, Er3+-Yb3+- Li+:Gd2O3 and Er3+-Yb3+- Zn2+:Gd2O3 nanophosphors respectively. The photometric characterizations of the developed nanophosphors have also been reported.

Influence of Dy3+ ions doping on structural and luminescent properties of GdVO4

Herein, the effects of Dy3+ doping concentration on the structural and photoluminescence properties of Dy3+ activated tetragonal GdVO4 matrix, synthesized via the co-precipitation method, have been presented in detail. The infrared spectroscopic studies confirmed the presence of vibrational bonds corresponding to Gd-O at 433 cm−1 and V–O at 830 cm−1, respectively. The microscopic studies elaborated nanosized spherical particles. Upon UV excitation, the as-prepared GdVO4: xDy3+ samples exhibited intense blue and yellow emissions due to 4F9/2 to 6HJ (J = 15/2, 13/2), respectively. The dominant peak at 574 nm was due to hypersensitive electric dipole transition 4F9/2 → 6H13/2 (∆J = 2) of Dy3+ ions. Above 1 mol% of doping, the quenching in PL intensity was observed due to inter ionic energy transfer among Dy3+ ions. The non-radiative energy transfer between Dy3+ ions was attributed to multipolar interactions. The critical distance of the energy transfer was calculated to be 25 A. Photometric characterizations confirmed its applicability in solid state lighting and display.

Enhanced red emission on co-doping of divalent ions (M2+ = Ca2+, Sr2+, Ba2+) in YVO4:Eu3+ phosphor and spectroscopic analysis for its application in display devices

This paper reports the enhancement in photoluminescence due to the alkaline ions (M2+) co-doping in YVO4:Eu3+ phosphors prepared by solid state reaction method. The as synthesized samples were found to have single phase tetragonal structure and the incorporation of dopant/codopant did not affect the crystal structure. The characteristic bands of YO and VO were located at 450cm−1 and 830cm−1, respectively. The microscopic images exhibited the irregular morphology of the synthesized phosphor consisting of μm sized particles. Upon UV excitations, all phosphors showed intense red–orange emissions corresponding to the 5D0→7FJ=1,2:Eu3+ transitions, and the emission intensity was further enhanced due to codoping. Divalent ions introduced radiative defect centers, which enhances the PL intensity significantly. The calculation of spectral parameters was done through Judd–Ofelt theory from emission spectra. The photometric characterizations and corresponding calculations indicated the suitability of the phosphor for display devices.

Polarimetric NIR reflectance measurements of regolith simulants at zero phase angle

Polarimetric reflectance measurements have been made at a wavelength of ∼ 1 μ m for a suite of predominantly lunar regolith simulants in support of development efforts for the BepiColombo Laser Altimeter (BELA). Measurements were made using an instrument at the University of Bern, Switzerland, that has been modified to accommodate photometric characterizations of laboratory samples down to 0 ∘ phase angle ( g ) with linearly polarized illumination and a linearly polarized receiver. The data reveal opposition surges that are dominated by polarization state-conserving reflectance terms for all samples. Relative strengths of the trans-state reflectance terms are lowest for the darkest samples, suggesting that multiple scattering is responsible for state conversions. Normal albedo measurements of the lunar simulants range from 0.13 to 0.22 at zero illumination angle ( i = 0 ∘ ). The total reflectance of the regolith simulants at g = 0 ∘ were found to decrease with increasing i , which is inconsistent with predictions of reflectance models for Mercury. However, the g = 0 ∘ reflectance remains higher at i > 0 ∘ than would be expected for a gray Lambert surface that is scaled to the g = i = 0 ∘ reflectance value. Polarization ratios for reflectance under polarized illumination but unconstrained emission show that the samples scatter light in the in-plane polarization state more efficiently than in the transverse state at g = 0 ∘ and i > 0 ∘ . The opposite is true for g > 0 ∘ polarization ratios, which indicate that transverse polarized illumination scatters more efficiently at high g . The polarization effect appears to correlate with the sample's characteristic grain size, but the statistical basis of this trend is weak. The implications of these measurements upon the performance of the BELA instrument are discussed.

Photometric characterization of an all solid state inorganic electrochromic large area device

An electrochromic large area device has been produced by Isoclima using a physical vapour deposition technique. The electrochromic coating has a five layer thin film structure and all the layers have been deposited in the same vacuum environment using the same technique. Two specimens with different sizes, 50×50 mm 2 and 300×300 mm 2, were prepared to be submitted to spectrophotometric and variable angle photometric characterization, respectively. The surface density of charge in both states (coloured and bleached) was obtained from the voltage step response recorded in terms of current density versus time. These measurements were performed during the spectrophotometric and photometric characterizations. Colour and (near) normal incidence luminous and solar parameters of the elctrochromic device were obtained by suitable integration of spectral transmittance and reflectance curves. Luminous transmittance and reflectance values of the electrochromic device under collimated variable angle or diffuse irradiation were directly measured by photometry. The photometric data were used to simulate the performances of the electrochromic device used in real conditions as a transparent part of a large window of a room. A computer code named Heatlux was used to evaluate the luminance distribution on the working plane in the room. Location of the building, orientation of the façade, geometry of the room, wall thickness and size of the windows were all considered in the simulation.