Optimization Of Optical Properties Research Articles

Recent Advances in the Growth and Compositional Modelling of III–V Nanowire Heterostructures

Nanowire heterostructures offer almost unlimited possibilities for the bandgap engineering and monolithic integration of III–V photonics with Si electronics. The growth and compositional modelling of III–V nanowire heterostructures provides new insight into the formation mechanisms and assists in the suppression of interfacial broadening and optimization of optical properties. Different models have been proposed in the past decade to calculate the interfacial profiles in axial nanowire heterostructures mainly grown by molecular beam epitaxy and metal–organic vapour phase epitaxy. Based on various assumptions, existing models have different sets of parameters and can yield varying results and conclusions. By focusing on deterministic models based on classical nucleation theory and kinetic growth theory of III–V ternary monolayers in nanowires, we summarize recent advancements in the modelling of axial heterostructures in III–V nanowires, describe and classify the existing models, and determine their applicability to predictive modelling and to the fitting of the available experimental data. In particular, we consider the coordinate-dependent generalizations of the equilibrium, nucleation-limited, kinetic, and regular growth models to make interfacial profiles across axial heterostructures in different III–V nanowires. We examine the factors influencing the interfacial abruptness, discuss the governing parameters, limitations, and modelling of particular material systems, and highlight the areas that require further research.

Spatially Resolved Optical Efficiency Measurements of Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are able to concentrate both direct and diffuse solar radiation, and this ability has led to great interest in using them to improve solar energy capture when coupled to traditional photovoltaics (PV). In principle, a large-area LSC could concentrate light onto a much smaller area of PV, thus reducing costs or enabling new architectures. However, LSCs suffer from various optical losses which are hard to quantify using simple measurements of power conversion efficiency. Here, we show that spatially resolved photoluminescence quantum efficiency measurements on large-area LSCs can be used to resolve various loss processes such as out-coupling, self-absorption via emitters, and self-absorption from the LSC matrix. Further, these measurements allow for the extrapolation of device performance to arbitrarily large LSCs. Our results provide insight into the optimization of optical properties and guide the design of future LSCs for improved solar energy capture.

High-throughput synthesis of silver nanoplates and optimization of optical properties by machine learning

High-throughput synthesis of silver nanoplates was performed by two-step reduction via the seed particles to clarify how the absorption spectrum is controlled by the concentrations of AgNO3 and citrate for the seed particle synthesis and that of the seed particles for the nanoplate synthesis. A wide variety of the concentrations, whose combination amounted to 486 conditions, was explored with an automated liquid handler, and the absorption spectrum was measured with a microplate reader. The spectrum was decomposed into two peaks, one around 400 nm from the spherical seed particles and the other at longer wavelength from the nanoplates. The nanoplate peak’s wavelength, width, and height were expressed as functions of the concentrations of AgNO3, citrate, and seed particles by non-linear support vector regression. This enabled us to predict optimum conditions for synthesizing nanoplates with high and narrow absorption peaks at desired wavelengths ranging widely from 450 to 900 nm.

Optimization of optical properties and durability performances of amorphous IZO transparent conductive films by preparing silicone coatings

In this study, the effect of silicone coatings on optical properties and durability performances of amorphous ln2O3:Zn (IZO) transparent conductive films is investigated. The average transmittance in visible wavelength of the IZO films increases from 77.5% to 84.3% by preparing silicone coatings on the surface, corresponding that the Haccke’s figure of merit (FOM) increases from 6.4 × 10−3 Ω−1 to 1.47 × 10−2 Ω−1. The reason is that the silicone coatings with low refractive index is considered as an antireflective layer. Both simulation and experiments demonstrate that the average transmittance is independent on silicone coatings thickness while the silicone coatings thickness is above 1.0 μm. After exposing in a damp-heat test at 60 °C and 95% relative humidity for 28 days, the sheet resistance and microscopic images of the IZO films with silicone coatings at different thickness are nearly no variation, indicating an excellent durability performance. While the sheet resistance of the IZO films without silicone coatings increases slightly and the corrosion on the surface is observed visually. It is concluded that the water vapor is the key reason for the degradation of the IZO films by investigating the microscopic images of the IZO films after exposing in the different environments.

On the efficient optimization of optical properties of particulate monolayers by a hybrid finite element approach

This article addresses the numerical simulation and optimization of the optical properties of mono-layered nano-particulate films. The particular optical property of interest is the so-called haze factor, for which a model close to an experimental setup is derived. The numerical solution becomes very involved due to the resulting size of computational domain in comparison to the wave length, rendering the direct simulation method infeasible. As a remedy, a hybrid method is suggested, which in essence consistently combines analytical solutions for the far field with finite element-based solutions for the near field. Using a series of algebraic reformulations, a model with an off- and online component is developed, which results in the computational complexity being reduced by several orders of magnitude. Based on the suggested hybrid numerical scheme, which is not limited to the haze factor as objective function, structural optimization problems covering geometrical and topological parametrizations are formulated. These allow the influence of different particle arrangements to be studied. The article is complemented by several numerical experiments underlining the strength of the method.

Effect of borate and bismuth glass compositions on luminescence properties of rare earth ions

Rare earth (RE) doped luminescent materials (glasses, glass-ceramics and nanophosphors) are widely studied due to their numerous applications in the field of solid state lasers, optical telecommunication, near infrared (NIR)-to-visible up-converting (UC) luminescence for biolabels, solar cells, white light emitting diodes, optical sensors, etc. The spectroscopic techniques are used to identify the best optimum glass composition and active ion concentration to get efficient luminescence. The importance of bismuth borate glasses, optimization of optical properties and active ion concentration have been carried out through spectroscopic techniques. The present paper reports the effect of bismuth borate glasses on luminescence properties of Ce3+, Nd3+ and Sm3+ ions. Judd-Ofelt theory has been used to quantify the fluorescence properties of luminescent levels.

Mixed vanadates: Optimization of optical properties by varying chemical composition

Mixed LuxY1-xVO4 crystals, undoped and doped with Eu3+, were synthetized by the solid state reaction method. The crystal structure and phase composition were controlled by the X-ray diffraction (XRD), Raman analysis, and scanning electron microscope (SEM) measurements. The samples' crystallinity was improved by annealing. Nevertheless, the lattice distortion caused by the substitution of Y by Lu was detected. The lattice parameters derived from the XRD data are in good agreement with the calculated ones. It was found that the luminescence intensity increase in the annealed samples is related to the improvement of crystallinity of samples. According to the studies of X-ray excited luminescence at 300K the relative luminescence intensity increases for the samples with intermediate values of x. For the LuxY1-xVO4:Eu3+ the highest luminescence intensity was detected for x=0.7 and ascribed to the effect of decrease of the mean distance between the thermalized electrons and holes. For the undoped crystals the luminescence is partially quenched at 300K, however the sample with x=0.7 demonstrate highest intensity as well. The effect in the undoped samples is due to the increase of the temperature of luminescence quenching in samples with intermediate values of x.

Optimization of Optical Properties of Nanocrystals in the Context of Functionality

Optimization of Optical Properties of Nanocrystals in the Context of Functionality

Tuning Hierarchical Cluster Assembly in Pulsed Laser Deposition of Al-doped ZnO

ABSTRACTThe synthesis of hierarchically assembled Al-doped ZnO layers by Pulsed Laser Deposition (PLD) at room temperature was investigated. PLD was performed in a background pressure of 100 Pa O2 to deposit clusters in a low energy regime and obtain nano- and mesostructures resulting from a hierarchical assembly of nanoclusters. We here analyzed the effects of varying the gas flow rate on mesoscale morphology, mass density and optical properties. The variation of the target-to-substrate distance was also investigated, identifying its effects on mass density and film morphology. The optimization of optical properties in terms of transparency and light scattering capability is of potential interest for photovoltaic applications.

Structure and distortion of lead fluoride nanocrystals in rare earth doped oxyfluoride glass ceramics

A series of rare earth (RE) doped oxyfluoride glasses with the composition of (45-x) SiO2-5Al2O3-40PbF2-10CdF2-xRe2O3 (x = 1, 5, 10, 15) (mol%) were prepared by a traditional melt-quenching method. Glass ceramics (GCs) were obtained after thermal treatment and characterized by X-ray diffraction (XRD) to investigate the nanocrystal structure and distortion. Both the dopant type and the doping level play an important role in the distortion of the PbF2-RE lattice. It is found that a cubic Pb3REF9 phase forms in low doping GCs, a tetragonal PbREF5 phase forms in middle doping GCs and cubic PbRE3F11 forms in high doping GCs. Accordingly, the site symmetry of RE(3+) dopants in β-PbF2 nanocrystal undergoes a transition of Oh···D4h···Oh with the increase of doping level. The change in the ligands coordinating the RE(3+) ions was further illustrated by the optical changes in Yb-doped GCs. This paper provides insights on the nanocrystal structure of RE at the atomic level and tries to make a complete description of the nanocrystal structure and distortion in these glass-ceramic materials, which will benefit the optimization of optical properties.

PNA/dsDNA Complexes: Site Specific Binding and dsDNA Biosensor Applications

The ability of peptide nucleic acids (PNA) to form specific higher-order (i.e., three- and four-stranded) complexes with DNA makes it an ideal structural probe for designing strand-specific dsDNA biosensors. Higher-order complexes are formed between a dye-labeled charge-neutral PNA probe and complementary dsDNA. Addition of a light-harvesting cationic conjugated polymer (CCP) yields supramolecular structures held together by electrostatic forces that incorporate the CCP and the dye-labeled PNA/DNA complexes. Optimization of optical properties allows for excitation of the CCP and subsequent fluorescence resonance energy transfer (FRET) to the PNA-bound dye. In the case of noncomplementary dsDNA, complexation between the probe and target does not occur, and dye emission is weak. The binding between PNA and noncomplementary and complementary dsDNA was examined by several methods. Gel electrophoresis confirms specificity of binding and the formation of higher-order complexes. Nano-electrospray mass spectrometry gives insight into the stoichiometric composition, including PNA/DNA, PNA(2)/DNA, PNA/DNA(2), and PNA(2)/DNA(2) complexes. Finally, structural characteristics and binding-site specificity were examined using ion mobility mass spectrometry in conjunction with molecular dynamics. These results give possible conformations for each of the higher-order complexes formed and show exclusive binding of PNA to the complementary stretch of DNA for all PNA/DNA complexes. Overall, the capability and specificity of binding indicates that the CCP/PNA assay is a feasible detection method for dsDNA and eliminates the need for thermal denaturing steps typically required for DNA hybridization probe assays.