Ultraviolet Peak Research Articles

Fabrication of Ultraviolet Photodetectors Based on Fe-Doped ZnO Nanorod Structures.

In this paper, 100 nm-thick zinc oxide (ZnO) films were deposited as a seed layer on Corning glass substrates via a radio frequency (RF) magnetron sputtering technique, and vertical well-aligned Fe-doped ZnO (FZO) nanorod (NR) arrays were then grown on the seed layer-coated substrates via a low-temperature solution method. FZO NR arrays were annealed at 600 °C and characterized by using field emission scanning microscopy (FE-SEM) and X-ray diffraction spectrum (XRD) analysis. FZO NRs grew along the preferred (002) orientation with good crystal quality and hexagonal wurtzite structure. The main ultraviolet (UV) peak of 378 nm exhibited a red-shifted phenomenon with Fe-doping by photoluminescence (PL) emission. Furthermore, FZO photodetectors (PDs) based on metal–semiconductor–metal (MSM) structure were successfully manufactured through a photolithography procedure for UV detection. Results revealed that compared with pure ZnO NRs, FZO NRs exhibited a remarkable photosensitivity for UV PD applications and a fast rise/decay time. The sensitivities of prepared pure ZnO and FZO PDs were 43.1, and 471.1 for a 3 V applied bias and 380 nm UV illumination, respectively.

The Carnegie Supernova Project II

We present ultra-violet (UV) to mid-infrared (MIR) observations of the long-lasting Type IIn supernova (SN) 2013L obtained by the Carnegie Supernova Project II beginning two days after discovery and extending until +887 days (d). The SN reached a peak r-band absolute magnitude of ≈−19 mag and an even brighter UV peak, and its light curve evolution resembles that of SN 1988Z. The spectra of SN 2013L are dominated by hydrogen emission features, characterized by three components attributed to different emission regions. A unique feature of this Type IIn SN is that, apart from the first epochs, the blue shifted line profile is dominated by the macroscopic velocity of the expanding shock wave of the SN. We are therefore able to trace the evolution of the shock velocity in the dense and partially opaque circumstellar medium (CSM), from ∼4800 km s−1 at +48 d, decreasing as t−0.23 to ∼2700 km s−1 after a year. We performed spectral modeling of both the broad- and intermediate-velocity components of the Hα line profile. The high-velocity component is consistent with emission from a radially thin, spherical shell located behind the expanding shock with emission wings broadened by electron scattering. We propose that the intermediate component originates from preionized gas from the unshocked dense CSM with the same velocity as the narrow component, ∼100 km s−1, but also that it is broadened by electron scattering. These features provide direct information about the shock structure, which is consistent with model calculations. The spectra exhibit broad O I and [O I] lines that emerge at ≳+144 d and broad Ca II features. The spectral continua and the spectral energy distributions (SEDs) of SN 2013L after +132 d are well reproduced by a two-component black-body (BB) model; one component represents emitting material with a temperature between 5 × 103 and 1.5 × 104 K (hot component) and the second component is characterized by a temperature around 1–1.5 × 103 K (warm component). The warm component dominates the emission at very late epochs (≳+400 d), as is evident from both the last near infrared (NIR) spectrum and MIR observations obtained with the Spitzer Space Telescope. Using the BB fit to the SEDs, we constructed a bolometric light curve that was modeled together with the unshocked CSM velocity and the shock velocity derived from the Hα line modeling. The circumstellar-interaction model of the bolometric light curve reveals a mass-loss rate history with large values (1.7 × 10−2 − 0.15 M⊙ yr−1) over the ∼25−40 years before explosion, depending on the radiative efficiency and anisotropies in the CSM. The drop in the light curve at ∼350 days and the presence of electron scattering wings at late epochs indicate an anisotropic CSM. The mass-loss rate values and the unshocked-CSM velocity are consistent with the characteristics of a massive star, such as a luminous blue variable (LBV) undergoing strong eruptions, similar to η Carinae. Our analysis also suggests a scenario where pre-existing dust grains have a distribution that is characterized by a small covering factor.

Facile Synthesis of Luffa Sponge Activated Carbon Fiber Based Carbon Quantum Dots with Green Fluorescence and Their Application in Cr(VI) Determination.

Carbon quantum dots (CQDs) were prepared by a chemical oxidation method using luffa sponge based activated carbon fiber as the raw material. The obtained CQDs were well characterized. The fluorescence quenching effect of Cr(VI) ion on CQDs was investigated. The results show that the addition of Cr(VI) changes the intensity of the ultraviolet characteristic absorption peak of CQDs, and causes static quenching of the fluorescence of CQDs. With the increase in the Cr(VI) concentration, the fluorescence of CQDs was gradually extinguished linearly.

Acetylresveratrol as a Potential Substitute for Resveratrol Dragged the Toxic Aldehyde to Inhibit the Mutation of Mitochondrial DNA.

The aim of this study was to explore whether or not acetylresveratrol as a potential substitute for resveratrol dragged the toxic aldehyde to inhibit the mutation of mitochondrial DNA. The results revealed that the acetylresveratrol shifted ultraviolet peak of trans-crotonaldehyde from 316 to 311nm. In mitochondria, the acetylresveratrol split the ultraviolet peak at 311nm of trans-crotonaldehyde into 311nm and 309nm; the aldehyde Raman band of trans-crotonaldehyde was red shifted by the acetylresveratrol from 1689 to 1686cm-1 with obvious band decline; Raman bands at 1149cm-1, 1168cm-1, and 1325cm-1 of acetylresveratrol disappeared. In aldehyde dehydrogenase, the aldehyde Raman band of trans-crotonaldehyde was red shifted by the acetylresveratrol from 1689 to 1684cm-1 with band decline; Raman bands at 1150cm-1, 1168cm-1, and 1324cm-1 of acetylresveratrol declined. The weak acidic microenvironment was the best, for the acetylresveratrol dragged the toxic aldehyde of trans-crotonaldehyde. Compared with the resveratrol, the effect of the acetylresveratrol on the toxic aldehyde of trans-crotonaldehyde was very similar to that of the resveratrol. The acetylresveratrol is very suitable as a potential substitute for resveratrol dragged the toxic aldehyde to inhibit the mutation of mitochondrial DNA. Graphical Abstract In mitochondria, the Raman band of the toxic -CH=O of trans-crotonaldehyde (TCA) dragged by the Acetyl-Res from 1689 to 1686cm-1 with obvious band decline, while the Raman bands at 1149cm-1, 1168cm-1, and 1325cm-1 of the Acetyl-Res disappeared, respectively. The Acetyl-Res is very suitable as a potential substitute, for the Res dragged the toxic -CH=O of TCA to inhibit the mutation of mitochondrial DNA for anticancer.

Predicting the redshift on the ultraviolet spectrum using the peak area method.

The ultraviolet (UV) absorption peaks of NaCl, NaOH, and $\beta $β-phenylethylamine (PEA) in an aqueous solution move toward redshift. We proposed the peak area method for the quantitative analysis of PEA, NaCl, and NaOH. First, we obtained the predictable regularities of the redshift of the single component sample. Then, we obtained the regularities of the redshift of the UV spectrum for the mixture by the peak height and peak area methods. Finally, the BP-ANN algorithm was applied to determine the concentration of the mixture using the peak height and peak area method. The results of the testing set showed that correlation coefficients (${{\rm R}^2}$R2) of 0.992, 0.993, and 0.992 were obtained by peak height method and 0.997, 0.998, and 0.998 were obtained by peak area method for NaCl, NaOH, and PEA, respectively. Meanwhile, the relative errors of the prediction of NaCl, NaOH, and PEA obtained by peak area method were less than 3%, whereas the REP of NaCl, NaOH, and PEA obtained by peak height method were more than 5%. Compared with the results of the peak height method, the results showed that the peak area was more accurate than the peak height in predicting the redshift of the UV spectrum.

ZnO colloids and ZnO nanoparticles synthesized by pulsed laser ablation of zinc powders in water

ZnO nanoparticles (NPs) were synthesized by pulsed laser ablation of zinc powders suspending in deionized water. The synthesized ZnO NPs were characterized for morphology, structure and optical properties. The ZnO NPs have irregular shapes sized in 10–50 nm and possess a wurtzite structure with polycrystallinity in nature, and grew without a preferential orientation. The supernatant solutions obtained by laser ablation of zinc powders in water exhibit the typical optical absorption edge of wurtzite ZnO near 380 nm and emit a photoluminescence composed of a narrow ultraviolet peak and a broad visible band, characteristics of the near-band-edge emission and the deep-level defects related emission of ZnO, respectively. The formation of ZnO NPs was further confirmed by structural and optical characterization performed for the aggregated ZnO NPs obtained by drop-casting the ZnO colloidal solutions onto Si wafers. And the effects of annealing in N2 on the structure and photoluminescence of the ZnO NPs transferred on Si were also examined.

Molecular spectroscopic behaviors of beta-arbutin in anti-skin cancer

The purpose of this study was to explore the molecular spectroscopic behaviors of the beta-arbutin on the toxic aldehyde of trans-crotonaldehyde in anti-skin cancer. Results revealed that both hydroxymethyl and phenolic hydroxyl of beta-arbutin led to the shift of the maximum ultraviolet peak of trans-crotonaldehyde from a very significant absorption peak at 300 nm to a very weak absorption peak at 310 nm and the significant shift of the aldehyde Raman band at 1689/cm of the toxic trans-crotonaldehyde in mitochondria and aldehyde dehydrogenase, respectively. The beta-arbutin acting on the toxic trans-crotonaldehyde highlighted the potential of anti-skin cancer and provided a valuable clue for the new application of the beta-arbutin.

Fabrication and Characterization of UV Photodetectors with Cu-Doped ZnO Nanorod Arrays

In this study, metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors (PDs) based on Cu-doped ZnO (CZO) nanorods (NRs) were fabricated and investigated. The CZO NRs were prepared on a Corning glass substrate by the chemical bath deposition (CBD) method with photolithography processes. It was found that the diameter and length of ZnO NRs increased with Cu-doped concentration. The X-ray diffraction (XRD) analysis showed that the growth of NR arrays along the c-axis was hexagonal wurtzite crystal. Compared with pure ZnO NRs, it can be seen that the main UV peak (378 nm) of photoluminescence (PL) spectra showed a blue-shift phenomenon with the increase of Cu-doped concentration. Additionally, it was found that the rise and recovery time of such a fabricated PD were shortened under the UV illumination. The UV sensing properties of the CZO PDs were improved since the trapping and de-trapping of electrons by Cu-related complexes were faster than the adsorption and desorption of oxygen molecules. With a 3 V applied bias and 380 nm UV illumination, the optimal sensitivity of our PDs is 196.6.

Photo-assisted Ag/AgCl nanoparticle formation process can be used in the degradation of fluorescent dyes

In this paper, we found that silver ions can efficiently degrade xanthene-based fluorescent dyes during the formation of Ag/AgCl nanoparticles under photo-assisted action. The experimental results indicates that both the ultraviolet absorption peak and fluorescence peak of xanthene-based fluorescent dyes disappeared in the presence of silver ions when the solution was irradiated with blue-violet light, implying the efficient degradation of these fluorescent dyes. Transmission electron microscopy (TEM) and Dynamic light scattering (DLS) analysis suggested the formation of nanoparticles during this process. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and STEM-mapping confirmed that the main chemical component of the nanoparticles was Ag/AgCl. To the best of our knowledge, it was the first time that the photo-assisted formation process of Ag/AgCl nanoparticles has been applied for the degradation of xanthene-based fluorescent dyes in a wide pH range (2.0–11.0) despite that Ag/AgCl nanoparticles are also widely used in dye degradation, and our experimental results also showed that the formation of photo-assisted Ag/AgCl nanoparticles is more efficient than Ag/AgCl nanoparticles themselves in dye degradation.

Temperature-dependent photoluminescence of Cs2AgxNa1-xInCl6 microcrystals

Cs2AgxNa1-xInCl6 microcrystals (MCs) are synthesized using a solvothermal method. The regular variation of Na incorporation is characterized according to the intensity change of the X-ray diffraction and ultraviolet visible absorption peaks. Temperature-dependent photoluminescence (PL) properties of Cs2AgxNa1-xInCl6 MCs are studied by use of steady-state PL and time-resolved PL (TRPL) measurements. From steady-state PL, it is verified that the white-light emission primarily originates from self-trapped excitons (STEs) at low temperature (80–290 K). When the electron-phonon interactions become stronger, STEs are promoted to generate from free excitons (FEs). And the high temperature-dependent (293–450 K) PL reveals the thermal quenching process. Temperature-dependent TRPL demonstrates that the change of lifetimes is attributed to band-edge FEs state and STEs state. It is found that the electrically-driven PL decreases to 70% then becomes stable from 0 to 120 min when light-emitting diodes (LEDs) are fabricated to explore the thermal stability. Our results suggest these white-emission Cs2AgxNa1-xInCl6 MCs can be used as excellent materials for LEDs and provide reference to engineer such MCs toward practical optoelectronic applications.

Low temperature cathodoluminescence study of Fe-doped β-Ga2O3

Abstract Optical and electrical properties along the b-axis of Fe-doped β-Ga2O3 were studied using low temperature cathodoluminescence (CL) spectroscopy, optical absorption spectroscopy and current-voltage (IV) measurements. The optical absorption spectroscopy showed an absorption edge without near edge shoulder and the corresponding optical bandgap was calculated to be 4.45 eV using direct band gap treatment. The temperature dependent CL measurements exhibited a strong blue to ultraviolet (UV) band composed of multiple low intensity peaks in the blue range, a main blue peak, a main UV peak, and a weak UV band from the as-grown Fe-doped β-Ga2O3. After a controlled annealing in air, the emissions changed to a red to near infrared (R-NIR) band with two sharp peaks and an UV band that is resolved at room temperature to three UV broad peaks. The R-NIR sharp peaks from the air-annealed sample were ascribed to incorporation of nitrogen during air annealing.

Properties of ultraviolet phosphor for ion-beam-induced fluorescent microscopy technology

Abstract In this study, we have investigated the ultraviolet (UV) fluorescence properties of a phosphor (YPO4:Gd) sample from the irradiation of a scanning proton beam to evaluate its usefulness as a staining agent of ion-beam-induced fluorescence microscopy (IBIF). The phosphor was prepared using a co-precipitation method. Owing to the irradiation, the sample exhibited UV fluorescence with a peak wavelength of 312 nm. In the emission spectrum, the FWHM of the UV peak ≈ 6 nm. The light emission in the UV region and the narrow peak bandwidth are characteristics that are effective at minimizing the background fluorescence and allow high-sensitivity IBIF imaging. Moreover, it was confirmed that the phosphor had a considerable radiation endurance. In addition, we successfully obtained IBIF images and elemental maps simultaneously for a test sample containing YPO4:Gd powder. These results demonstrate that the prepared phosphor is suitable for IBIF.

Fabrication and optical property of ZnO nanorod array by hydrothermal method

We synthesize a large area of ZnO nanorod array by using the RF magnetron sputtering and low-temperature hydrothermal method. The sample morphology, crystal structure and optical properties are characterized and analyzed by means of the SEM, XRD and fluorescence spectrophotometer. The results show that ZnO nanorod array has the advantages of large aspect ratio, ordered orientation, uniform and compact at a lower OH−/Zn2+ concentration. The XRD results show that the samples are all hexagonal wurtzite structures and the photoluminescence (PL) pattern shows that an obvious ultraviolet peak of the samples appears around 375 nm, and an emission band of strong yellow green light appears in the wavelength between 450–650 nm. With the increase of the concentration ratio of OH−/Zn2+, the ultraviolet peak and the emission band of strong yellow green light both show a blue shift. The above results indicate that the ZnO nanorod array is a type of potentially preferred materials for ultraviolet optoelectronic devices.

Green synthesis of fluorescent Ag-anionic polyacrylamide nanoparticles gels solution with high stability via a simple template method

The fluorescent Ag-anionic polyacrylamide (Ag-APAM) hybrid nanoparticles (NPs) gels solutions were synthesized by using an environmental-friendly APAM template without extra reductant and stabilizer. The APAM with stretched molecule chains trended to absorb and reduce Ag+ to Ag0 under the UV-light of 365 nm. Moreover, the network structure formed by APAM can protect Ag NPs from the aggregation and the size of Ag NPs was about 4.2 nm. The pink Ag-APAM NPs gels solution can emit the fluorescence under the UV-light irradiating. The intensity of ultraviolet adsorption peak and the fluorescence increased with increasing the concentration of APAM. The maximum fluorescence intensity of the gels solution was obtained when the concentration of APAM is 25 µM. The as-prepared Ag-APAM NPs gels solution can keep stable for six months and will be applied in antibacterial gels.

Effects of aluminum doping on the structural and optical properties of ZnO nanorods grown on highly conductive films

ZnO nanorods were grown on ∼ 50-nm-thick transparent conductive oxide thin films by hydrothermal synthesis. The resistivity of the ZnO films was lowered to 4 × 10−4 Ω cm upon Ga doping. Zinc nitrate hexahydrate, mixed with hexamethylenetetramine, was dissolved in deionized water to prepare a synthesis solution. Aluminum nitrate nonahydrate was added to the synthesis solution to dope the Al into ZnO nanorods. X-ray diffraction analysis and field-emission scanning electron microscopy were conducted to study the crystal structure and morphology of the nanorods, respectively. Al doping enhanced the preferential orientation to (002) of a wurtzite structure and increased the compressive strain. The trace of Al in the ZnO nanorods was detected by energy dispersive X-ray spectroscopy. The optical properties were investigated by measuring the transmittance, Raman shift, and photoluminescence. Al doping led to a blue shift or red shift in the energy band gap. The results of the Raman shift confirmed the compressive stress in the ZnO nanorods. Sharp ultraviolet (UV) and broad visible photoluminescence peaks were obtained irrespective of Al concentration in the ZnO nanorods. The intensity of the UV peak doubled by Al doping.

High-aspect-ratio single-crystalline AlN nanowires: Free-catalytic PVT growth and field-emission studies

Nanowires (NWs) with high aspect ratios (HARs) have great advantages for the fabrication of nanodevices. Herein, a high-efficiency and simple physical vapor transport (PVT) method is utilized to synthesize the uniform HAR aluminum nitride (AlN) NWs on a tungsten substrate without any catalysts. Synergistic effect of high surface energy of (0001), low saturated vapor pressure and large axial temperature gradient leads to the growth of HAR AlN NWs, which provides new insight for the growth of low-dimensional AlN nanostructures. The as-obtained AlN NWs with super HAR have hexagonal wurtzite structure, the diameters are about 100 nm and the lengths are over 200 μm. The AlN NWs have an intensive deep ultraviolet (DUV) absorption peak at 5.94 eV and exhibit a relatively high electrical conductivity (1.29 × 10−3 Ω−1 cm−1), low turn-on field (6.2 V μm−1) and threshold field (8.5 V μm−1). These results indicate that PVT method is efficient to fabricate HAR AlN NWs and the AlN NWs not only play an important role in DUV photoelectric devices but also have tremendous potential as a candidate for field-emission nanodevices.

First Release of High-Redshift Superluminous Supernovae from the Subaru HIgh- Z SUpernova CAmpaign (SHIZUCA). I. Photometric Properties

We report our first discoveries of high-redshift supernovae from the Subaru HIgh-Z sUpernova CAmpaign (SHIZUCA), the transient survey using Subaru/Hyper Suprime-Cam. We report the discovery of three supernovae at the spectroscopically-confirmed redshifts of 2.399 (HSC16adga), 1.965 (HSC17auzg), and 1.851 (HSC17dbpf), and two supernova candidates with the host-galaxy photometric redshifts of 3.2 (HSC16apuo) and 4.2 (HSC17dsid), respectively. In this paper, we present their photometric properties and the spectroscopic properties of the confirmed high-redshift supernovae are presented in the accompanying paper (Curtin et al. 2019). The supernovae with the confirmed redshifts of z ~ 2 have the rest ultraviolet peak magnitudes close to -21 mag and they are likely superluminous supernovae. The discovery of three supernovae at z ~ 2 roughly corresponds to the approximate event rate of ~ 900 +/- 520 Gpc-3 yr-1 with Poisson error, which is consistent with the total superluminous supernova rate estimated by extrapolating the local rate based on the cosmic star-formation history. Adding unconfirmed superluminous supernova candidates would increase the event rate. Our superluminous supernova candidates at the redshifts of around 3 and 4 indicate the approximate superluminous supernova rates of ~ 400 +/- 400 Gpc-3 yr-1 (z ~ 3) and ~ 500 +/- 500 Gpc-3 yr-1 (z ~ 4) with Poisson errors. Our initial results demonstrate the outstanding capability of Hyper Suprime-Cam to discover high-redshift supernovae.

Physical properties of cost effectively synthesized ZnO nanowires post annealed under various thermal and atmosphere treatments for UV photodetectors

Vertically aligned Zinc Oxide nanowires (ZnO NWs) were grown on glass seeded substrates by the chemical bath deposition (CBD) method at a low temperature. Two parameters including temperature and atmosphere were varied while time and heating rate were kept constant. The field emission scanning electron microscopy images show that the ZnO NWs with a hexagonal cross section are grown perpendicular to the seeded glass substrates. The x-ray diffraction results reveal that all the ZnO NW arrays grow preferentially oriented along the c-axis in the direction of (002) plane with a hexagonal wurtzite structure. Photoluminescence measurements of the grown ZnO NWs on all samples exhibit a high ultraviolet (UV) peak intensity compared to a broad visible peak, which can be accounted for the formation of the high crystal quality ZnO NWs. Results show that the UV light emission is greatly enhanced by annealing the as-grown ZnO NWs in O2 ambient. Moreover, transient response measurement reveals that the detectors exhibit a fast photoresponse time of fewer than 5 s. In this annealing case, the quantum efficiency of UV detection reaches about 15%. Finally, a qualified metal-semiconductor-metal (MSM) ZnO photodetector was prepared from the annealed as-grown sample in the pure O2 ambient.

Degenerate intermodal four-wave mixing with Q-switched nanosecond pulses in SMF-28 for the generation of discrete ultraviolet-visible wavelengths

Intermodal four-wave mixing (IMFWM) is demonstrated in a standard SMF-28e + fiber through pumping in the normal dispersion regime by a Q-switched nanosecond pulsed laser. A new IMFWM process where two pump photons in LP01 mode are completely annihilated to give rise to Stokes and anti-Stokes photons, both in LP02 mode, has been observed. Discrete ultraviolet peaks at 390.7 nm and 396.7 nm are also observed in this communication fiber through a complex cascaded process.

Synthesis and Optical Properties of Solid and Hollow ZnO Microspheres Prepared by Hydrothermal Method

We successfully synthesized solid and hollow ZnO microspheres by a template-free hydrothermal method on the substrate of porous alumina membranes. The morphology of prepared sample was characterized by scanning electron microscopy and transmission electron microscopy. The growth mechanism of the synthesized ZnO microspheres is discussed in detail. At step 1, solid ZnO microspheres were prepared by the thermal decomposition of the Zn(OH)2 microspheres synthesized under the mixture of Zn(NO3)2·6H2O, C6H12N4, and C6H5Na3O7·2H2O solution. The quantity of C6H5Na3O7·2H2O dopant will greatly affect the morphology of the prepared sample by controlling ZnO nucleation and growth rate. At step 2, hollow ZnO microspheres were prepared by removing the Zn(OH)2 cores in an alkaline solution. The proper pH value also plays a key role in preparing hollow ZnO microspheres with high quality. Compared with hollow nanostructure, the solid ZnO microsphere shows the relatively strong Raman peaks at 437 cm-1, which suggests that the prepared solid spheres should have the better crystal quality. Photoluminescence spectra show that the solid ZnO microspheres have the relatively strong ultraviolet (UV) peak at ~ 380 nm attributed to the recombination of free exciton, and the weak green peak owing to the low surface-to-volume ratio. DOI: http://dx.doi.org/10.5755/j01.ms.24.4.19141