UV Wavelength Range Research Articles

Ultraviolet optical properties of CaSrF2 crystal grown by the cone die Czochralski method

Fluoride crystals with extremely wide band gaps are ideal optical materials in the UV wavelength range. Large 4-inch diameter calcium strontium fluoride (Ca0.582Sr0.418F2) single crystal was grown using the Czochralski method with a Cone-shape Die (CD-CZ). The refractive index and relative transmittance of the crystal was evaluated by cutting it into a triangular prism and polished. The direct measurement of the refractive index and relative transmittance was done by using a spectrograph to image the refraction of light as it passes through a dual prism set-up consisting of a SQ prism as reference and either CaF2 or Ca0.582Sr0.418F2 as the material under evaluation. Characterization results showed that Ca0.582Sr0.418F2 has excellent refractive index dispersion and transmittance in the UV region, confirming the applicability of the dual prism with spectrograph setup to measurements of the refractive index and relative transmittance in the UV region.

Sign reversal of visible to UV photocurrent in core–shell n-InGaN/p-GaN nanowire photodetectors

We demonstrate the change of the sign from negative to positive of the self-powered photovoltaic photocurrent in core–shell n-InGaN/p-GaN nanowire heterojunctions within the visible to UV wavelength range. Such dual-polarity photodetectors are of broad interest to provide extended functionalities for optoelectronic devices, starting with dual-wavelength photodetectors. The physics of the photocurrent sign reversal is understood by a well-balanced selective absorption and photocarrier generation, photocarrier transfer, and thermal excitation paths in the core–shell n-InGaN/p-GaN nanowire functional absorber with different bandgap energies and opposite inner- and surface energy band bendings. The basic dual-wavelength photodetector operation parameters are given.

High-energy acousto-optic Q-switched alexandrite laser with wavelength tunable fundamental and UV second harmonic generation

We investigate high-energy mJ-class diode-pumped acousto-optic (AO) Q-switched alexandrite lasers with broad tunability at both the fundamental near-IR wavelength range and second harmonic generation (SHG) in the UV wavelength range. An AO Q-switched alexandrite laser with continuous-wave diode-pumping has been operated at up to 10 kHz and producing pulse energy of 700 µJ at repetition rate of 1 kHz. With pulsed double-pass diode-pumping, we demonstrate higher pulse energy of 2.6 mJ. With wavelength tuning, this laser system demonstrated broad fundamental tuning range from 719 to 787 nm with diffraction-limited beam quality (M2 = 1.05). By external cavity second harmonic generation in a Type-I LBO crystal, pulse energy of 0.66 mJ is generated at 375 nm and with UV tuning range from 361 to 391 nm. To our knowledge, this is the first demonstration of AO Q-switched alexandrite laser with broad wavelength tuning in the near-IR and UV wavelength ranges and shows its excellent potential as a pulsed source for future applications.

The effects of etching time and hydrogen peroxide concentration on the ZnO/glass substrate

The purpose of the study is to determine the best technique for etching ZnO thin films. ZnO is deposited on the glass substrate using a radio frequency sputtering equipment. To etch the ZnO thin film, hydrogen peroxide (H2O2) concentrations of 10%, 20%, and 30% are utilised, with etching times of 30 and 60 seconds. The optical band gap is lowered after a specific quantity of etching, which shows that the film's crystallinity quality has improved. The impact of various ZnO thicknesses on the sample's optical properties is investigated using OPAL 2 simulator. In comparison to other ZnO layers of varied thickness, the OPAL 2 simulation shows that the 400 nm ZnO layer has the lowest transmission in the UV wavelength range.

The role of the epidermal physode layer in UV protection of Fucus species

Phlorotannins are believed to provide UV protection in brown algae. In Fucus species, phlorotannin-rich vesicles (“physodes”) form an “epidermal physode layer”, which might represent the anatomical structure responsible for UV protection. However, this layer has been neglected so far; instead, phlorotannin contents of entire thalli were studied in UV exposure experiments.We employed fluorometric methods to investigate in which wavelength region and to which degree the epidermal physode layer of two Fucus species reduces the transmittance of UV radiation. For comparison, we also studied Saccharina latissima, a brown algal species without epidermal physode layer.We could show that the epidermal physode layer absorbs throughout the entire UV wavelength range and reduces the epidermal UV-B transmittance into the thallus strongly (15% transmitted in F. vesiculosus vs. 80–100% in S. latissima). UV-B transmittances varied with growth depth and the variations correlated with photosystem II (PSII) stress responses upon artificial UV-B illumination. We found that the UV-B protection is more than sufficient for natural UV-B levels and of rather constitutive nature.In conclusion, the epidermal physode layer appears to be the anatomical feature exerting UV protection by phlorotannins in Fucus species and might thus be a core adaptation that enables Fucales the colonization of the intertidal habitat.

Theoretical investigation of the ground state dissociation pathways of CH2NO2

We report theoretical calculations of the nitromethyl radical (CH2NO2) ground state dissociation pathways. Calculations were performed using a combination of density functional theory (DFT) and coupled-cluster singles doubles and triples (CCSD(T)) with the cc-pVTZ basis set. The ground state unimolecular dissociation of the nitromethyl radical (CH2NO2) occurs via three dissociation pathways and we have characterized the transition state associated with the formation of NO + CH2O (channel I) which has a barrier height of 167.5 kJ/mol. We have also calculated the variational transition states associated with the CH2 + NO2 (channel II) and CH2NO + O (channel III) product channels. Thermal rate constants were calculated to model dissociations at temperatures relevant to shock tube experiments on nitromethane combustion. We find that the branching fractions vary over the range of temperatures relevant to nitromethane combustion, with channel II rising from <1% at 800 K to 14% at 2450 K, and channel I decreasing from >99% to 86% over the same range at one bar. RRKM theory was used to calculate unimolecular microcanonical rate constants at total energies corresponding to photoexcitation over a range of UV wavelengths from 279 to 228 nm to assess the relative branching fractions and compare to previous experimental data on the photodissociation of CH2NO2. The comparison reveals a disparity in the branching fraction between the calculation and experimental results, suggesting the possibility of an excited state dissociation pathway.

Luminescent Polymer Composites for Optical Fiber Sensors.

Optical fiber sensors incorporating luminescent materials are useful for detecting physical parameters and biochemical species. Fluorescent materials integrated on the tips of optical fibers, for example, provide a means to perform fluorescence thermometry while monitoring the intensity or the spectral variations of the fluorescence signal. Similarly, certain molecules can be tracked by monitoring their characteristic emission in the UV wavelength range. A key element for these sensing approaches is the luminescent composite, which may be obtained upon allocating luminescent nanomaterials in glass or polymer hosts. In this work, we explore the fluorescence features of two composites incorporating lanthanide-doped fluorescent powders using polydimethylsiloxane (PDMS) as a host. The composites are obtained by a simple mixing procedure and can be subsequently deposited onto the end faces of optical fibers via dip coating or molding. Whereas one of the composites has shown to be useful for the fabrication of fiber optic temperature sensors, the other shows promising result for detection of UV radiation. The performance of both composites is first evaluated for the fabrication of membranes by examining features such as fluorescent stability. We further explore the influence of parameters such as particle concentration and density on the fluorescence features of the polymer blends. Finally, we demonstrate the incorporation of these PDMS fluorescent composites onto optical fibers and evaluate their sensing capabilities.

Ultraviolet refractive index values of organic aerosol extracted from deciduous forestry, urban and marine environments

Optical trapping and Mie Spectroscopy are used to measure the refractive index of organic matter extracted from the atmosphere in the UV wavelength range.

Design of a Hybrid Refractive/Diffractive Lens System for Broadband UV.

Traditional broadband UV optical designs often have complex structural problems and cannot meet the current requirements of light and miniaturization. In this study, we first design the substrate material of double-layer diffractive optical elements (DOEs) in the 0.23-0.8 μm band, optimize the diffraction efficiency and analyze the effect of the angle of incidence on the diffraction efficiency of double-layer DOEs. Second, we design a refractive lens system and a refractive/diffractive hybrid lens system with double-layer DOEs designed for a wide UV wavelength range of 0.23-0.8 μm, a half field of view of 15 mm, an objective aperture of 0.1 and a magnification of 1. The refractive/diffractive hybrid lens system designed with seven lenses produces a higher image quality than the refractive lens system. The novel design is an effective solution to the problem of the low transmission rate of traditional UV refractive lens systems.

Length-Dependent Photocatalytic Activity of Hybrid Ag-CdS Nanorods

Hybrid metal–semiconductor nanostructures are promising photocatalysts for a wide span of reactions. Determining the relationship of their geometry with catalytic efficiency is critical for optimization of the catalysts. In this work, Ag-CdS nanorods with five different lengths (from 25.0 to 106.5 nm) have been synthesized using a seed-mediated growth method. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) studies confirmed that the formation of a metal tip and semiconductor body part and they absorb strongly and broadly in the UV and visible wavelength range. The nanorods have been employed as photocatalysts for methyl orange degradation and their catalytic efficiency exhibited length-dependence. Specifically, the highest efficiency was observed in the rods of intermediate length (72.1 nm). Time-dependent photoluminescence decay revealed that the Ag-CdS rods with high catalytic efficiency have a higher probability to go through charge-separation-recombination pathway than the rods with low catalytic efficiency. Understanding the physical process in these hybrid structures provides insight into fine-tuning their geometry to improve the charge transfer efficiency from the metal to the semiconductor domain. Thus, better hybrid nanomaterials can be designed and fabricated for photocatalytic and other applications.

Plasmonic Properties of Al2O3 Nanoshell with a Metallic Core

Background: Al is the promising candidate for deep UV and longer wavelength range plasmonic applications. But it is difficult to have the pure aluminium nanostructure as it is easily oxidized, forming a thin layer of Al2O3. In this paper, we have evaluated the field enhancement of oxide layer on metallic shell (Al-Al2O3 and Au-Al2O3) for single and dimer core-shell configuration and showed potential of the oxide layer in SERS. Methods: The Finite Difference Time Domain (FDTD) has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3 and Au- Al2O3 nanostructure. Results: The results exhibit the tunable plasmon resonance on varying the inner and outer radii of the Al2O3 shell. A redshift and decrease in enhancement were observed as shell thickness increases, whereas on increasing the core size, the enhancement increases in the case of Au-Al2O3 and decreases in Al- Al2O3 due to quadrupole contribution. But on comparing the Au-Al2O3 with Al-Al2O3 for the same particle size, Al-Al2O3 shows larger enhancement because Au has to compete with its interband transition. Conclusion: By optimizing the thickness of the shell and core size, it can be concluded that an ultrathin shell of Al2O3 can give higher enhancement. With Al as a core metal, the enhancement increases as compared to Au-Al2O3. Since a single Al-Al2O3 nanoshell has shown a huge enhancement we have considered the multimer configuration of two identical nanoshells. Due to coupling between two nanoshells a huge increase in enhancement factor ~1012 was observed for Al-Al2O3 dimer nanoshell in the UV region.

Medium-term prediction of the fluence of relativistic electrons in geostationary orbit using solar wind streams forecast based on solar observations

The new approaches to the modelling of the Sun-solar wind-magnetosphere-radiation belts chain and their implementation at MSU's Space weather center (Space Monitoring Data Center, SMDC) are presented. The main idea is to use data from medium-term (3–5 days) forecasts of the speed of quasi-stationary solar wind streams based on data obtained from solar images in the UV wavelength range to improve the quality of forecasts of the magnetospheric factors of the space environment. An operational model for predicting the daily fluence of relativistic electrons (>2 MeV) in the Earth's outer radiation belt has been developed, with the extended set of input parameters that include the forecast of the solar wind velocity. To validate the model, the period from October 11, 2016 to February 18, 2017 was considered, during which the Sun made several revolutions and it was possible to observe the evolution of coronal holes and the development of solar sporadic phenomena. The arrival of high-speed solar wind streams from coronal holes to the Earth's magnetosphere, as well as, as impact of coronal mass ejections, provoked geomagnetic disturbances of various intensity, and caused significant variations of the electron fluxes of the Earth's outer radiation belt. SMDC website implements solar wind model based on the data of solar observations by the AIA instrument of the SDO space observatory at wavelengths of 19.3 and 21.1 nm that forecasts the daily fluence of relativistic electrons (E > 2 MeV) in geostationary orbit. It is shown that the use of the results of medium-term forecasting of the solar wind speed as an input parameter in the daily electron fluence forecast model can significantly improve its quality with a forecast horizon of up to 4 days.

LSPR‐Enhanced Pyro‐Phototronic Effect for UV Detection with an Ag–ZnO Schottky Junction Device (Adv. Mater. Interfaces 23/2022)

Self-Powered Photodetector A strategy to enhance the photothermal conversion of UV light by LSPR of silver nanoparticles (Ag NPs) is proposed by Jianping Meng, Zhou Li, and co-workers in article number 2200327. After decorating Ag NPs, the photodetector based on the Schottky junction of Ag and ZnO nanowires (NWs) can detect the UV light with low power density. The enhanced performance is attributed to the high-quality factor of Ag NPs in UV wavelength range, which can raise temperature variation of ZnO NWs noticeably when turning on/off light.

Rovibrational investigation of a new high-lying 0u + state of Cu2 by using two-color resonant four-wave-mixing spectroscopy.

A highly excited electronic state of dicopper is observed and characterized for the first time. The [39.6]0u +-X1Σg +(0g +) system is measured at rotational resolution by using degenerate and two-color resonant four-wave-mixing, as well as laser induced fluorescence spectroscopy. Double-resonance experiments are performed by labeling selected rotational levels of the ground state by tuning the probe laser wavelength to transitions in the well-known (1-0) band of the B0u +-X1Σg +(0g +) electronic system. Spectra obtained by scans of the pump laser in the UV wavelength range were then assigned unambiguously by the stringent double-resonance selection rules. The absence of a Q-band suggests a parallel transition (ΔΩ = 0) and determines the term symbol of the state as 0u + in Hund's case (c) notation. The equilibrium constants for 63Cu2 are Te = 39 559.921(92)cm-1, ωe = 277.70(14)cm-1, Be = 0.104 942(66)cm-1, and re = 2.2595(11) Å. These findings are supported by high-level ab initio calculations at the MRCI+Q level, which clearly identifies this state as resulting from a 4p ← 3d transition. In addition, three dark perturber states are found in the v = 1 and v = 2 vibrational levels of the new state. A deperturbation analysis characterizes the interaction and rationalizes the anomalous dips in the excitation spectrum of the [39.6]0u +-X1Σg +(0g +) system.

Cover Feature: Photoionization, Structures, and Energetics of Na‐Doped Formic Acid–Water Clusters (ChemPhysChem 5/2022)

The Cover Feature shows the natural difference orbital profiles of the first electronic excited states in the UV wavelength range of Na⋅⋅⋅HCOOH⋅⋅⋅(H2O)n clusters. The existence of these Rydberg–type electronic transitions could explain the cluster ionization at laser energy lower than their vertical ionization potential, enabling the correct data interpretation on acid-water cluster formation. More information can be found in the Research Article by Tonia M. Di Palma and co-workers.

Effective UV wavelength range for increasing aflatoxins reduction and decreasing oil deterioration in contaminated peanuts

Many studies have demonstrated that UV radiation can degrade aflatoxins (AF) in contaminated foods. However, the effective wavelength ranges for AF decomposition and their impacts on the quality of foods have not been elucidated. This study investigated the AF reduction and oil quality change in peanuts subjected to three types of 17 W low-pressure (LP) UV lamps covering UV-A (Max. emission: 365 nm), UV-B (Max. emission: 310 nm), and UV-C (Max. emission: 254 nm) ranges and a 2000 W medium-pressure UV lamp covering from UV-A to UV-C. We used peeled-kernels for this study since the peanut skin represented an ability to protect AF from being degraded by UV. LP UV-A lamp treatment has shown the highest AF reduction in artificially spiked peeled-kernels and no detectable oil deterioration. With the same delivered UV dosage as LP lamp, MP lamp has shown the same level of AF reduction as LP UV-A lamp did, indicating such treatment was energy inefficient. Treating Aspergillus nomius inobulated peeled-kernels by two LP UV-A lamps (2.76 mW/cm2) for 1.0 h reduced 40% of AF if the kernels were milled into 1 mm-diameter particle, implying that exposing the interior part of kernels to UV radiation is necessary for an AF decontamination process. In the oil deterioration test, we found that UV-C strongly induced the oil oxidation of peanuts. Accordingly, we concluded that UV-A is the effective wavelength range to degrade AF as well as maintain the oil quality in foods allowing UV radiation to well penetrate the sample, such as liquid foods with low turbidity or solid foods in the particle form. These results also justify the use of solar radiation as an AF decontamination method, rendering this method to be employed in in areas that lack infrastructure.

Modeling AlGaN p-i-n photodiodes

Ternary AlGaN alloys with a band gap of 3.4 to 6.2 eV are very promising for photodetectors in the UV wavelength range. Using the COMSOL MULTIPHYSICS software based on AlGaN, a p-i-n photodiode model was developed, including its I–V characteristic, spectral sensitivity of the received radiation, absorption coefficient as a function of the aluminum fraction and the depletion layer thickness. To calculate the process of interaction of a semiconductor with EM radiation, we used a model based on the use of an element of the transition matrix through the carrier lifetime during spontaneous recombination. In this case, the peak sensitivity of the photodiode is from 0.08 to 0.18 A/W at wavelengths of 0.2–0.33 µm. This is in line with experimental results taken from the relevant literature.

Simulation of the photonic nanojet effect for Raman scattering enhancement in the diagnostics of oxide films

In this paper, by means of numerical simulations in the COMSOL Multiphysics software it’s demonstrated that Raman scattering enhancement can be achieved for the diagnosis of metal oxide films using spherical particles made of barium titanate with a 10-micron diameter sphere. The formation of photonic nanojet in the sphere/film/substrate system at different radiation wavelengths and microsphere refractive index, film, and substrate was studied. The optimal interval of the particle refractive index is n≈1.8-2 was determined, at which the gain occurs directly at the particle/film interface. It is shown that for the UV wavelength range of wavelengths and film thicknesses from 50 to 200 nm, the gain is maximum. For ZnO and PZT films in the perovskite phase, sitall and quartz are preferred as the substrate material, while for PZT in the pyrochlore phase, sapphire is preferred.

An Experimental and Theoretical Study of Dye Properties of Thiophenyl Derivatives of 2-Hydroxy-1,4-naphthoquinone (Lawsone).

A prospective study of the dye properties of non-toxic lawsone thiophenyl derivatives, obtained using a green synthetic methodology allowed for the description of their bathochromic shifts in comparison to those of lawsone, a well-known natural pigment used as a colorant that recently also has aroused interest in dye-sensitized solar cells (DSSCs). These compounds exhibited colors close to red, with absorption bands in visible and UV wavelength range. The colorimetric study showed that these compounds exhibited a darker color than that of lawsone within a range of colors depending on the substituent in the phenyl ring. Computational calculations employing Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT), showed that the derivatives have lower excitation energies than lawsone, while the alignment of their frontier orbitals regarding the conduction bands of TiO2 and ZnO and the redox potential of the electrolyte I−/I3− suggests that they could be employed as sensitizers. The study of the interactions of the lawsone and a derivative with a TiO2 surface model by different anchoring modes, showed that the adsorption is thermodynamically favored. Natural bond orbital (NBO) analysis indicates a two-center bonding (BD) O-Ti as the main interaction of the dyes with TiO2.

UV–Vis–NIR broadband response of GaAs-based photocathode with multilayer graded-band cascade structure

To improve the lattice matching, quantum efficiency and response range of the transmission-mode GaAs-based photocathode , a novel photocathode with multilayer graded-band cascade emission layer is proposed. The one-dimensional steady-state continuity equations and finite-difference time-domain methods are utilized to obtain the quantum efficiency and optical absorption characteristics of the proposed photocathode, respectively. The results show that, the built-in electric fields generated by the varying-composition and varying-doping structure can assist the photoelectrons generated in the sublayer itself and the front sublayers to transport towards the emitting surface and escape to the vacuum. Compared with the conventional AlGaAs/InGaAs structure, the proposed structure possesses better lattice matching and enhanced quantum efficiency in the UV and NIR wavelength range. A three-fold increase of quantum efficiency can be realized at 400 nm and the theoretical quantum efficiency at 1064 nm can reach 2%. Besides, the integral absorptivity is increased by 6.8% in the visible wavelength range, and 12.9% in the NIR wavelength range. It is found that the increase of the thickness of AlGaAs sublayer and GaAs sublayer mainly reduces the quantum efficiency in the UV–Vis wavelength range. When the InGaAs sublayer is thin enough, the increase of thickness would enhance the quantum efficiency in the NIR wavelength range and deteriorate that in the UV–Vis wavelength range. This work can contribute to the performance improvement of UV–Vis–NIR broadband GaAs-based photocathode. • A transmission-mode photocathode with multilayer graded-band cascade structure is proposed. • The quantum efficiency model of the proposed multilayer structure is deduced. • The quantum efficiency and optical absorption characteristics are investigated. • The lattice matching, quantum efficiency and response range are improved.