ultraviolet-B Region Research Articles

Characterization of the Ultraviolet-B Absorption Band of Carotenoids Using Solvent-dependent Shifts in Steady-State and Transient Absorption Spectra.

The versatile functions of carotenoids in biological systems are associated with the extended π-electron conjugation system. Strong visible absorption resulting from the optically allowed S2 (1Bu+) state and the low-lying optically forbidden S1 (2Ag-) state examined. Carotenoids also exhibit an absorption band in the ultraviolet-B region; however, the origin of this band (hereafter referred to as Suv state) is not well characterized. The Suv state is a candidate for the destination level of the well-known S1 → Sn transient absorption; however, an obvious energy mismatch has been observed. In this study, we examined the steady-state and picosecond transient absorption spectra of lycopene in various solvents. The Suv absorption of carotenoids with diverse conjugation lengths was also examined. The dependence of the energies on solvent polarizability and conjugation length revealed that both Suv and Sn are the "second" Bu+ state. The absorption spectrum for lycopene at 200 K revealed an additional vibrational band, which may be the vibrational origin of the S0 → Suv band. Considering the slow vibrational relaxation of the 2Ag- state, the S1 → Sn transition may represent the 2Ag- (v = 1) → 2Bu+ (v = 0) transition, and the energetic contradiction can be resolved.

Synthesis and study of optical properties of a Gd3+-doped NaYF4 phosphor for phototherapy lamp application.

In recent trends, radiation falls under the narrowband ultraviolet-B region (305-315 nm) widely used in phototherapy lamp applications in the treatment of skin diseases. In this paper, we report a Gd3+-doped NaYF4 luminescent material synthesized for the first time using the low-temperature co-precipitation method. It crystallized into a face-centred cubic structure, as confirmed by X-ray diffraction characterization techniques and Rietveld refinement. The photoluminescence property of the as-prepared sample shows a highly intense, sharp emission band obtained at 311 nm, which belongs to the narrowband ultraviolet-B region and corresponds to the transition of the 6P7/2→8S7/2 level of the Gd3+ ions under 272 nm excitation (8S7/2 to 6IJ). The transitions of the Gd3+ ions are detected entirely with different concentrations of Gd3+ ions. Scanning electron microscopy analysis indicated that the average particle was 288 nm. The critical distance for energy transfer was calculated to be equal to 11.5017 Å. Dipole-dipole interaction is responsible for energy transfer, as analyzed by Dexter theory. These excellent optical characteristics, together with their highly efficient and low-cost synthesis approach, indicate that synthesized NaYF4:Gd3+ phosphors have excessive potential for phototherapeutic lamp applications.

Thermodynamic, electronic, and optical properties of ultra-wide bandgap zirconium-doped tin dioxide from a DFT perspective.

The effects of zirconium doping on the thermodynamic, electronic, and optical properties of tin dioxide are investigated by using density functional theory calculations combined with the cluster expansion method. In the whole composition range, the formation enthalpies of all structures are positive, indicating that SnO2-ZrO2 is an immiscible system and the ZrSnO2 alloy has a tendency of phase separation at low temperature. The x-T phase diagram of ZrSnO2 ternary alloy shows that the critical temperature is 979 K, which means that when the growth temperature of ZrSnO2 crystal is higher than the critical temperature, it is possible to realize the full-component solid solution. The bandgaps of ZrxSn1-xO2 alloys (0 ≤ x ≤ 1) are direct and increase as the Zr composition increases. Zr doping can tune the bandgap of SnO2 from the ultraviolet-B region to the deep ultraviolet region, and has a strong optical response to deep ultraviolet light. The projected density of states and band offsets clearly reveal the reason for the increase of bandgap, which provides useful information to design relevant optoelectronic devices such as quantum wells and solar-blind deep ultraviolet photodetectors.

Photoluminescence and EPR spectroscopic studies on narrowband ultraviolet-B (NB-UVB) emitting trivalent gadolinium-doped CaAl4O7 material for phototherapy lamps

Using the sol-gel process, a series of Gd3+ doped CaAl4O7 samples were fabricated. Their crystal characteristics, surface morphologies, and spectral characteristics were analyzed using X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. XRD analysis reveals that the prepared phosphor exhibits a single monoclinic phase, indicating a well-defined crystal lattice. Under the excitation wavelength of 272 nm, weak and strong emission peaks were identified at 307 nm and 314 nm, which correspond to 6P5/2 → 8S7/2 and 6P7/2 → 8S7/2 transitions, respectively. A strong electron paramagnetic resonance (EPR) signal of the CaAl4O7:Gd3+ phosphor was observed at geff ∼ 2.16 and 1.94 along with several weak EPR signals that were observed at geff ∼ 14.8, 9.7, 5.6, 4.8, 3.7, 3.16, 2.7 and 1.5. The intense narrowband at 314 nm in the ultraviolet-B region makes prepared phosphor a promising candidate for phototherapy lamp applications. This study presents a comprehensive investigation of the Gd3+ doped CaAl4O7 phosphor, addressing its structural, and luminescent properties, which contributes to a deeper understanding of this material for various technological applications.

Ultraviolet-B radiation from Gd (III) doped hardystonite

Abstract Trivalent gadolinium (Gd3+)-doped calcium zinc silicate (Ca2ZnSi2O7/hardystonite) with a molar composition of Ca2−x ZnSi2O7:xGd3+ (x = 0.09 mol) was produced using a sol–gel system. The hardystonite was characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The X-ray diffraction study revealed that the prepared sample contained a tetragonal phase of Ca2ZnSi2O7. The vibrational structures of the sample were studied using Fourier transform infrared spectroscopy measurements. The photoluminescence emission spectrum of the Ca1.91ZnSi2O7:0.09Gd3+ phosphor narrow band was optimized at 312 nm in the Ultraviolet-B region under excitation at 273 nm wavelength. Electron paramagnetic resonance study authenticates the presence of gadolinium (Gd) ions within the trivalent state in the Ca1.91ZnSi2O7:0.09Gd3+ host.

Emission from Storage Phosphors That Glow Even in Bright Ambient Light

Light-emission phenomena of storage phosphors have received widespread attention, provoking the continuous developments of persistent luminescence, photostimulated luminescence, and mechanoluminescence. In the study and application of storage phosphors, as a matter of experience, it is always necessary to avoid or eliminate ambient light. It is the requirement for ambient darkness that is hindering the further development of storage phosphors under different ambient conditions. Here, we report an interesting glow phenomenon of storage phosphors in bright ambient light by introducing a concept termed ambient stimulated emission, in which the ambient temperature and ambient lighting can simultaneously release energy stored in the storage phosphors and lead to long-lasting emissions beyond the visible spectrum. As a proof of concept, we focus our discussion on an x-ray-charged ${\mathrm{La}\mathrm{Mg}\mathrm{Al}}_{11}{\mathrm{O}}_{19}:{\mathrm{Gd}}^{3+}$ phosphor, which exhibits ambient stimulated emission in the ultraviolet-B region, with increased initial light emission when the phosphor is exposed to ambient illumination instead of dark conditions. The ambient-stimulated-emission performances are found to depend on the illuminance and spectral distribution of ambient light. Moreover, our study indicates that the glow phenomenon in bright ambient light commonly appears in various storage phosphors, involving ultraviolet and infrared phosphors. The introduction of ambient stimulated emission brings different insights to luminescence research and offers approaches to further learn about and utilize storage phosphors.

White-light flashlight activated up-conversion luminescence for ultraviolet-B tagging.

Optical tagging technology with emission in the ultraviolet region upon visible-light excitation is promising for objects identified in visually bright environments, while the relevant research is absent. Here we put forward a covert tagging concept, which is based on up-converting phosphors (e.g., Lu3Al5O12:Pr3+) with emission peaking in the ultraviolet-B region (UV-B, 290-320 nm). A white-light flashlight serves as excitation source to make the up-converter emit, and an ultraviolet camera is applied to see such an emission wavelength range. This Letter expands the excitation source for an up-conversion process to a convenient flashlight for the first time, to the best of our knowledge. Moreover, such a flashlight-pumped UV-B tagging technology is generally applicable for many other phosphors, which can be utilized to mark and differentiate objects in commercial, civilian, or military applications.

Low Operating Voltage Solution Processed (Li₂ZnO₂) Dielectric and (SnO₂) Channel-Based Medium Wave UV-B Phototransistor for Application in Phototherapy

UV lamps used for phototherapy for the treatment of several skin diseases do not have uniform output. This makes the treatment difficult and less responsive. A Ultraviolet B (UV-B) sensitive thin-film phototransistor has been fabricated and characterized to monitor the intensity of UV radiation in phototherapy of skin diseases like psoriasis, vitiligo, and atopic dermatitis. Phototherapy with UV-B ranges from 280 to 320 nm, safe and very effective for skin disease treatment. Hence, to make it portable and affordable for medical technologies, we have demonstrated the fabrication process of a low-operational (≤2V), low-cost solution-processed Li2ZnO2 (dielectric)/SnO2 (channel)-based phototransistor that shows very high photosensitivity at around ~300 nm of UV-B region. The working principle depends on the passage of UV-B light through a window followed by striking a micrometer-scale semiconductor phototransistor. The responsivity and external quantum efficiency (EQE) of the fabricated phototransistor was found to be about 0.12 A/W and 40.12% at 300 nm, respectively, at a notably low operating voltage (≤2 V). High sensitivity (>200%) with fast response time (7 s) was also achieved with UV-B irradiation of 650 $\mu \text{W}$ /cm2. For in-depth performance analysis of the fabricated device, modeling has also been done, and the outcome matched well with the experimental results.

MgZnO-Based Schottky Barrier Ultraviolet-B Photodiode by Ultrasonic Spray Pyrolysis Deposition

This article demonstrates a Mg0.4Zn0.6 O-based ultraviolet-B photodiode using ultrasonic spray pyrolysis deposition (USPD). The material characteristics of the USPD-deposited Mg0.4Zn0.6O thin film are investigated by the X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and ellipsometer. Schottky photodiode is fabricated by using Pt as the anode and Ti/Au as the cathode. Note that 0.84-eV Schottky barrier height is formed between Pt and Mg0.4Zn0.6O. The present Schottky barrier photodiode shows high rectification ratio of 104 and high ultraviolet-to-visible rejection ratio of ${1.83} \times {10}^{{5}}$ . Furthermore, the specific detectivity is over 1011 Jones at ultraviolet-B region.

UVB in solar-simulated light causes formation of BaP-photoproducts capable of generating phosphorylated histone H2AX

Polycyclic aromatic hydrocarbons (PAHs), wide-spread mutagenic and carcinogenic environmental pollutants, are consistently exposed to sunlight in the environment. Our previous paper showed that benzo[ a]pyrene (BaP) exposed to solar-simulated light (SSL) induced phosphorylation of histone H2AX (γ-H2AX) [T. Toyooka, G. Ohnuki, Y. Ibuki, Solar-simulated light-exposed benzo[a]pyrene induces phosphorylation of histone H2AX, Mutat. Res. 650 (2008) 132–139], a marker of DNA double strand breaks. In this study, we found the ultraviolet B (UVB) region of SSL to produce photomodified BaP with high cytotoxicity and the ability to generate γ-H2AX. Degradation of BaP by SSL, resulting in an increase in cytotoxicity and the generation of γ-H2AX, was decreased by UVB-masking using a glass plate. Exposure to UVB itself increased the cytotoxicity of BaP and amount of γ-H2AX generated. Other PAHs, 1,2-benzoanthracene and 1,2:5,6-dibenzoanthracene, which absorb UVB, also showed enhanced cytotoxicity and the promoted the generation of γ-H2AX after exposure to SSL, whereas naphthalene and chrysene, which have low absorption in the UVB region, did not. These findings suggested that UVB is important for the degradation of PAHs having absorbance in this region, but that the production of genotoxic intermediates during the degradation process needs to be considered. UVB is a two-edged blade in environments, effectively degrading toxic chemicals but also producing genotoxic compounds as reactive intermediates.

An Integrating UVB Dosemeter System

Recent evidence of sharp increases in the number and severity of deformations in many amphibian species worldwide resulting from increased ultraviolet-B (UVB) exposure has prompted the development of a new integrating UVB dosemeter system. This dosemeter can be read out using either thermoluminescence (TL) or optically stimulated luminescence (OSL) techniques. The detection method takes advantage of the photqtransfer properties of Al 2 O 3 :C in the UVB region (280-320 nm). These UVB dosemeters have a linear dynamic range of several orders of magnitude and no significant temperature dependence. The inherent angular dependence of the interference filter has been flattened using diffusers and the increased phototransfer efficiency of Al 2 O 3 :C at shorter UVB wavelengths. The new UVB dosemeters can be used in air or in water and require no external power source. Their small, lightweight and watertight design make them ideally suited for measuring the UVB exposure of amphibian egg sacks in situ.

A stabilized transfer-standard system for spectral irradiance

High-power quartz-halogen lamps have been in use as transfer standards for a long time. However, even the best lamps available are not stable enough to match the increasing requirements stemming from the progress of measuring techniques. In particular, long-term stability in the ultraviolet-B region has to be improved. In order to achieve higher stability, it is necessary to change the operating conditions from constant-current to a detector-controlled system. The new OMTec transfer-standard system, consisting of a control unit including power supply and a lamp detector unit, is described. Its main features are: long-term stability with a deviation of the spectral radiant flux from the calibration values of less than 3 × 10-5 h-1 during nearly 400 hours of operating time throughout the spectral range from the ultraviolet-B to the near-infrared; continuous check on stability by monitoring and viewing the measured detector photocurrents; reduction of the required seasoning time by a factor of three thus enhancing the lifetime of the lamp; storage of lamp and calibration data in the lamp detector unit for external use.

In situ calibration technique for UV spectral radiometers

A technique for calibrating spectral radiometers measuring global (2π sr) irradiance using solar irradiance at the top of the atmosphere as the absolute irradiance reference is reported. In addition to providing a calibration at all measured wavelengths, the technique provides a direct measure of the angular response of the radiometer. For instruments that can be used to measure the ultraviolet-B region, the calibration also provides an estimate of the ozone column amount.

UV-B protective potential and flavonoid content of leaf hairs of Quercus ilex

Flavonoids of non-glandular leaf hairs from Quercus ilex were analysed. The main compounds were acylated kaempferol glycosides. Acylation shifted the absorption peak into the ultraviolet-B region of the spectrum in which intact trichome layers absorbed strongly. Ultraviolet-B radiation caused a considerable reduction of photosystem II photochemical efficiency only in dehaired leaves. It is suggested that leaf hairs, besides other roles, may function as an effective filter against the harmful ultraviolet-B radiation.

Photodegradation of sulfamethoxazole: a chemical system capable of monitoring seasonal changes in UVB intensity.

Sulfamethoxazole (SMX) in its nonionized form in aqueous solution has ultraviolet (UV) absorption that is maximal at 268 nm but extends through the ultraviolet-B (UVB) region. It was found to be extremely susceptible to photodegradation when exposed to artificial UV radiation through a Pyrex filter or to unfiltered natural sunlight. The SMX anion was more stable. The quantum yields of the photodegradation of both forms were determined by use of monochromatic light and ferrioxalate chemical actinometry, the values of 0.47 (pH 3.0) and 0.084 (pH 9.0) at the maximum absorption wavelengths (268 and 257 nm, respectively) being obtained. Using literature data on sunlight intensity, the photochemical shelf-life of SMX solutions exposed to direct sunlight was calculated for Sydney (latitude 33.5 degrees S) as a function of season of the year and verified experimentally. A fixed correlation was established between the rate constant for SMX degradation and UVB intensity measured by a radiometer, suggesting the capacity of this chemical system to monitor changes in the UVB region of sunlight.