UV-A Emission Research Articles

Super long ultraviolet-A persistent luminescence and photo-stimulated luminescence from CaMgGeO4: Bi3+

Here, we have developed a novel ultra long ultraviolet-A afterglow material CaMgGeO4: Bi3+, which shows more than 24 h UVA afterglow emission peaked at 346 nm. The crystal structure shows that the prepared sample is a pure phase with an orthogonal system of Pmnb space group. The composition of valence band and conduction band was analyzed by the density of states, which reveals that the bandgap of the CaMgGeO4 matrix is 3.69 eV. The photoluminescence spectrum of the sample consists of a broadband in the 320–400 nm UVA region, which belongs to the 3P1 → 1S0 electron transition of Bi3+. More importantly, under the excitation of ultraviolet lamp for 3 min, CaMgGeO4: Bi3+ exhibited an UVA ultra long persistent luminescence (LPL) with a duration of more than 24 h, which afterglow emission intensity still reaches 1500 cps and is about 6 times of the background intensity. In addition, the UVA emission of CaMgGeO4: Bi3+ after 13 h day can be repeatedly by short periods of low-energy light sources stimulation. The thermoluminescence analysis indicates that the presence of shallow and deep traps is responsible for excellent UVA-LPL and photo-stimulate luminescence (PSL). The excellent LPL and PSL properties can prompt CaMgGeO4: Bi3+ phosphor to be widely used in the field of photodynamic therapy.

Novel Fluorescent Tetrahedral Zinc (II) Complexes Derived from 4-Phenyl-1-octyl-1H-imidazole Fused with Aryl-9H-Carbazole and Triarylamine Donor Units: Synthesis, Crystal Structures, and Photophysical Properties.

We present here the design, synthesis, and photophysical properties of two novel fluorescent zinc (II) complexes, ZnCl2(ImL1)2 and ZnCl2(ImL2)2, containing 4-(1-octyl-1H-imidazol-4-yl)-N,N-diphenyl-[1,1-biphenyl]-4-yl)-4-amine ImL1 and 9-(4-(1-octyl-1H-imidazol-4-yl)-[1,1-biphenyl]-4-yl)-9H-carbazole ImL2 ligands. The newly synthesized free ligands and their zinc (II) complexes were characterized using several spectroscopic techniques; their structures were identified by single-crystal X-ray diffraction; and their photophysical properties have been studied in the context of their chemical structure. The ZnCl2(ImL1)2 and ZnCl2(ImL2)2 complexes showed good thermal stability at 341 °C and 365 °C, respectively. Photophysical properties, including UV-Vis absorption spectra in ethanol solution and photoluminescence (PL) in both solid state and ethanol solution, were determined. UV-Vis adsorption data indicated that both free ligands had similar UV-Vis absorption properties, while their Zn (II) complexes had distinctive absorption characteristics. The fluorescence spectra show that both ligands and their corresponding Zn (II) complexes emit violet to cyan luminescence in the solid state at room temperature, while in ethanol solution at the same temperature, they exhibit efficient photoluminescence properties in the UV-A emission spectral region. Because of these photophysical properties, the synthesized ligands and their cognate Zn (II) complexes can be used as scaffolds for the potential development of optoelectronic materials.

Photostability and characterization of spray-dried maltodextrin powders loaded with Sida rhombifolia extract

Sida rhombifolia extracts, obtained by pressurized liquid extraction (PLE), were microencapsulated in maltodextrin (MD) by spray drying. Different formulations were prepared with MD at 20% (w/w) and with 2.5, and 5.0% of S. rhombifolia extract, called ME2.5, and ME5.0, reaching an encapsulation efficiency of 89, and 94%, respectively. Scanning electron microscopy (SEM) and fluorescence microscopy enable the determination of the particles average size of 3.07 μm, and confirmed the extract encapsulation in MD. Besides, the phenolics autofluorescence allowed the correlation with the extract compounds, mainly 3-O-β-D-glycoside . The Fourier transform infrared (FTIR) results show no interaction between the coating material (MD) and the microcapsules core (extract). The produced powder was characterized by colorimetric analyzes, solubility isotherms, kinetics, and moisture adsorption, in addition to thermal analyzes. Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) indicated 64.6 and 53.4% of mass loss for ME2.5 and ME5.0, respectively. The microparticles photostability, evaluated in a self-assembled UVA/UVB emission chamber, showed 93.8 and 84.5% stabilization of total phenolic compounds (TPC) for ME2.5 and ME5.0, respectively. Given the high encapsulation efficiency and the preservation of extract quality, this study results suggest the possibility to use the loaded microcapsules in formulations for food and nutraceutical industries. • Phenolic compounds from Sida rhombifolia leaves were microencapsulated with spray-dry maltodextrin. • SEM and fluorescence morphological analysis confirm the true encapsulation of the extract by maltodextrin. • A UVA and UVB emission chamber was built, with a temperature sensor and air exhaust system. • The photostability of phenolic compounds present in the microencapsulated extract was evaluated by UVA and UVB emission. • The encapsulation process has shown optimal efficiency and represents good prospects for industrial deployment.

Beyond 53% internal quantum efficiency in a AlGaN quantum well at 326 nm UVA emission and single-peak operation of UVA LED: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 495 (2020)OPLEDP0146-959210.1364/OL.376894.

Evaluation of UVA emission from x-ray megavoltage-irradiated tissues and phantoms

RECA (Radiotherapy enhanced with Cherenkov photo-activation) is a proposed treatment where the anti-cancer drug psoralen is photo-activated in situ by UVA (Ultraviolet A, 320–400 nm) Cherenkov light (CL) produced directly by the treatment beam itself. In this study, we develop a UVA-imaging technique to quantify relative UVA CL produced by bulk tissues and other phantoms upon clinical x-ray megavoltage irradiation. UVA CL emission (320–400 nm) was quantified in tissue samples of porcine and poultry and in two kinds of solid waters (SW): brown (Virtual Waters, Standard Imaging, WI) and white (Diagnostic Therapy, CIRS, VA), and in 1% agarose gels variously doped with absorbing dye. Quantification was achieved through cumulative imaging of the samples placed in a dark, light-blocking chamber during irradiation on a Varian 21 EX accelerator. UVA imaging required a specialized high-sensitivity cooled camera equipped with UVA lenses and a filter. At 15 MV, white SW emitted , and less UVA than chicken breast, pork loin and pork belly, respectively. Similar under-response was observed at 6 MV. Brown SW had less UVA emission than white SW at 15 MV, and negligible emission at 6 MV. Agarose samples (1% by weight) doped with 250 ppm India ink exhibited equivalent UVA CL emission to chicken breast (within 8%). The results confirm that for the same absorbed dose, SW emits less UVA light than the tissue samples, indicating that prior in vitro studies utilizing SW as the CL-generating source may have underestimated the RECA therapeutic effect. Agarose doped with 250 ppm India ink is a convenient tissue-equivalent phantom for further work.

Super‐Long Persistent Luminescence in the Ultraviolet A Region from a Bi3+‐Doped LiYGeO4 Phosphor

AbstractHere, a novel super‐long, ultraviolet A region (UVA), persistent luminescent (PerL) material, LiYGeO4:Bi3+, is developed. After irradiation at 254 nm for 10 min, the UVA PerL of LiYGeO4:Bi3+ can persist for more than 300 h. In addition, the LiYGeO4:Bi3+ also possesses a strong UVA emission with a power density of 11.83 mW m−2 at 10 s after the removal of the excitation source. Even after 72 h, the UVA PerL emission spectrum can still be clearly detected, which is the same as the photoluminescence emission spectrum and originated from the Bi3+ emitting centers. Furthermore, LiYGeO4:Bi3+ also exhibits a photostimulated PerL property, which can be easily activated with a red light emitting diode (LED) or NIR laser irradiation after the long‐term decay. Combining the results of the PerL excitation, absorption, and thermoluminescence spectra, the excellent UVA PerL of LiYGeO4:Bi3+ can be ascribed to the existence of abundant trap sites created by the loss of Li+. This excellent PerL material can make up for deficiency of PerL materials in the UVA region and greatly expand the application of PerL materials in the biomedical, energy, environmental, and catalysis fields.

Influence of ultraviolet wavelengths on kinetics and selectivity for N-gases during TiO2 photocatalytic reduction of nitrate

For drinking water applications, photocatalytic reduction processes beneficially transform aqueous nitrate to innocuous nitrogen gases (N-gases) but can produce nitrite and ammonia as undesirable aqueous by-products. We hypothesize that by-product selectivity is a function of light source and photon fluence dose, such that discrete wavelengths can increase yield of desirable N-gases. Experiments performed under different wavelength irradiation (ultraviolet- [UV] A, B, C) reduced nitrate in water to differing extents based on pH over the range of 1–8 or the presence of soluble organic electron donors. At an equivalent photon fluence dose, the most rapid nitrate loss in acidic solutions occurred using a combination of three UV-light emitting diodes (285nm, 300nm, 365nm) closely followed by a polychromatic medium pressure UV lamp. A polychromatic xenon light source was least effective in reducing nitrate. Nitrite is an important intermediate during photocatalytic reduction of nitrate. Nitrite absorbs 330–380nm light with high quantum efficiency. Thus, polychromatic or monochromatic light sources with strong UV-A emission more rapidly convert nitrite to by-products than UV-C monochromatic light sources. Nitrous acid (HONO) has a higher molar absorptivity (ε) and quantum efficiency than nitrite ion (pKa=3.39) around 350–370nm. Selectivity towards N-gases is bifurcated at the nitrite intermediate and is strongly influenced by direct photolysis instead of photocatalytic reduction. Thus, the selectivity of by-products can be controlled by delivering light in the 350–370nm wavelength range, where it enables photocatalytic processes to rapidly initiate NO3− reduction and delivers photons for direct photolysis of HONO.

Investigation on physical properties of L-alanine: An effect of Methylene blue dye

In the present investigation, a bulk size (35 mm × 25 mm × 15 mm) single crystal of 0.1 wt% Methylene blue dye (MLB) added L-alanine is grown at room temperature using solution technique for the first time. The L-alanine crystals with higher concentrations of dye (0.5 and 1 wt%) were also grown. Solubility study was performed at different temperatures. Structural, vibrational and good quality was inveterate by powder XRD, FT-Raman and SEM analyses. High transmittance in dyed crystals was confirmed. The presence of MLB dye was confirmed by an absorption band centered at 650 nm. Optical band gap was calculated for pure and dyed L-alanine crystals and found to be 5.45 and 4.49 eV respectively. Photoluminescence intensity of UV-A emission band centered at 332 nm was found to be enhanced due to the presence of dye. The dielectric measurement was done in the wide frequency range. Furthermore, the third order nonlinear optical parameters are enhanced in dyed L-alanine crystals determined by Z-scan technique.

Defect-rich ZnO quantum dots as a potential multifunctional sunscreen and cosmetic active ingredient

Abstract In sunscreens, ZnO nanoparticles (NPs) are used as inorganic UV filter which have a prominent band edge emission in the UVA region (~385 nm). When applied to biological surface, this highly penetrating UVA emission from ZnO NPs would enhance the generation of reactive oxygen species resulting in oxidative stress. Therefore, the elimination of this harmful UVA emission from ZnO NPs are much sought after for the development of safer sunscreens. In this paper we introduce the use of defect-rich ZnO (D-ZnO) quantum dots (QDs) as a multifunctional active ingredient in sunscreen/cosmetic application. These D-ZnO QDs make use of their defect energy levels to emit in visible region by bypassing their harmful band edge emission at UVA region. The D-ZnO QDs also showed prominent visible luminescence which matches well with the autofluorescence of in vivo human skin. Hence, this visible luminescence could be useful for camouflaging, thereby enabling its potential as a biologically safe active ingredient for both cosmetic and UV screening applications.

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV)

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim.

UV-A emission from fluorescent energy-saving light bulbs alters local retinoic acid homeostasis

Worldwide bans on incandescent light bulbs (ILBs) drive the use of compact fluorescent light (CFL) bulbs, which emit ultraviolet (UV) radiation. Potential health issues of these light sources have already been discussed, including speculation about the putative biological effects on light exposed tissues, yet the underlying mechanisms remain unclear. We hypothesized photoisomerization of all-trans retinoic acid (at-RA), a highly light sensitive morphogen, into biologically less active isomers, as a mechanism mediating biological effects of CFLs. Local at-RA is anti-carcinogenic, entrains molecular rhythms and is crucial for skin homeostasis. Therefore, we quantified the impact of CFL irradiation on extra- and intracellular levels of RA isomers using an epidermal cell culture model. Moreover, a biologically relevant impact of CFL irradiation was assessed using highly at-RA-sensitive human neuroblastoma cells. Dose-dependent conversion of extra- and intracellular at-RA into the biologically less active 13-cis-isomer was significantly higher in CFL vs. ILB exposure and completely preventable by employing a UV-filter. Moreover, pre-irradiation of culture media by CFL attenuated at-RA-specific effects on cell viability in human at-RA-sensitive cells in a dose-dependent manner. These findings point towards a biological relevance of CFL-induced at-RA decomposition, providing a mechanism for CFL-mediated effects on environmental health.

Effect of solution chemistry on organic fouling of reverse osmosis membranes in seawater desalination

The influence of pH and calcium ion concentrations on the organic fouling of reverse osmosis (RO) membranes was investigated under two distinguished ionic strengths representing surface water (i.e., 10 mM) and seawater conditions (i.e., 600 mM). Variations in flux decline with respect to the feed water pH and calcium concentrations under these ionic environments were compared. Organic foulants deposited on the membrane surface were collected and characterized in terms of specific UVA (SUVA) and fluorescence excitation and emission matrix (FEEM) in conjunction with XAD-8/4 resin fractionation. Flux-decline curves obtained by various feed water pH and calcium concentrations under the low ionic strength condition were quite different with each other, while flux-decline curves obtained at the seawater-level ionic strength was almost identical regardless of variations in the feed water pH and calcium concentration. SUVA and FEEM results showed that the characteristics of organic matters attached on the membrane surface at high ionic strengths were significantly different from those at low ionic strengths. SUVA values and FEEM images indicated that organic foulants at the seawater-level ionic strength were mostly hydrophobic. Consequently, enhanced hydrophobic interaction dominantly controlled the rate and the extent of organic fouling at seawater-level ionic strength where the impacts of feed water pH and calcium were significantly masked.

Click chemistry for photonic applications: triazole-functionalized platinum(ii) acetylides for optical power limiting

Three different triazole-containing platinum(II) acetylide compounds were synthesized by click chemistry and evaluated for their use in optical power limiting (OPL) applications. The triazole unit was incorporated at three different positions within, or at the end of, the conjugation path of the chromophore. The aim is to explore the possibilities of using click chemistry to prepare dendronized chromophores, and to evaluate how the triazole structure affects the photophysical properties and the optical power limiting abilities of these acetylide compounds. It is shown that the concept of click chemistry can be used to attach branched monomer units to ethynyl-phenyl arms by Huisgen 1,3-dipolar cycloaddition, forming triazole units within the chromophore. Photophysical characterization of these triazole-containing materials shows an absorption maximum within the UV-A region and emission through both fluorescence and phosphorescence. Bright phosphorescence was emitted from argon purged samples, and decay measurements thereof showed triplet lifetimes of up to 100 µs. The results from the photophysical characterization suggest that the triazole does break the conjugation path, and in order to gain maximum optical limiting the triazole needs to be placed at the end of the conjugation. All three investigated triazole-containing platinum(II) acetylides show good optical power limiting at 532 nm (10 ns pulse, f/5 set-up, 2 mm cells). The most efficient compound, with the triazole positioned at the end of the conjugation, reaches a defined clamping level of 2.5 µJ for a sample with a concentration of 50 mM in THF and a linear transmission above 80% at 532 nm. These data can be compared to the OPL properties of Zn-based porphyrins or derivatized thiophenes, reaching clamping levels of 6–15 µJ.

Illuminance and UV-A exposure during rearing affects egg production in broiler breeders transferred to open-sided adult housing

1. Broiler breeders were reared in light-proof accommodation on 8-h photoperiods at an illuminance of 10 (W10), 40 (W40) or 100 lux (W100) from warm-white fluorescent lamps, or 10 lux (UV10) from Arcadia bird lamps (white light plus UV-A emission). At 20 weeks, 200 birds from each group were transferred to open-sided housing and a 16-h mixture of natural and warm-white fluorescent light. 2. Mortality during rearing and body weight at 20 weeks were similar for all groups. 3. The W10 birds matured 2 d later, had inferior rates of lay over peak production and laid 9 fewer eggs to 60 weeks than the other groups. Mean egg weight, extra large egg production and mortality between 20 and 60 weeks were unaffected by lighting during the rearing period. The UV10 birds had a significantly better rate of lay between 52 and 60 weeks than any of the groups reared on white light. 4. The findings suggest that ultraviolet radiation does not directly affect hypothalamic activity, but that retinally received UV during the rearing period prolongs the laying cycle through a modification of the hormonal control of photorefractoriness.

The French Regulations for Ultraviolet Radiation Sunbeds

The French Ministry of Health took the responsibility of legislating on the sale and public access to UV tanning appliances, expecting to improve the safety of tanning booths and to discourage the population from sun-tanning. The legislation is based on the IEC 337-2-27 international standard adopted by AFNOR (France). Only types 1 and 3 tanning appliances are authorised for public use, types 2 with high UVB and unlimited UVA emission, and 4, being reserved for medical use. The law specifies that type 1 and 3 tanning appliances should emit less than 1.5% UVB (<320 nm) in radiant energy of total emission. Exclusion of minors, mandatory notices, content of notices, and information for users are included in the law. The appliances in use must be declared to the National Health Authorities, inspected within two years and every five years thereafter (specific protocol) by appointed organisations whose operators must have received specific training. Major defects (90% of electric defects) were found in 50% of the first 600 controlled tanning sites.

UV-B induced differential transcription of psbD genes encoding the D2 protein of Photosystem II in the cyanobacterium Synechocystis 6803.

UV-B irradiation of intact Synechocystis sp. PCC 6803 cells results in the loss of Photosystem II activity, which can be repaired via de novo synthesis of the D1 and D2 reaction center subunits. A key step in the repair process is the differential transcription of the psbA2 and psbA3 genes, coding for identical D1 polypeptides [Máté et al. (1998) J Biol Chem 273: 17439-17444]. In the present work, we investigated for the first time the effect of UV-B irradiation on the transcription of the psbD1 and psbD2 genes encoding identical D2 polypeptides. By using gene-specific S1 nuclease protection assay we showed differential UV-B induced transcription of the two psbD genes: the level of psbD1 mRNA was increased 1.5-2 fold, whereas the accumulation of psbD2 mRNA was 5-7 fold. The induction of psbD2 transcript accumulation by low intensity light was specific for the UV-B range. UV-A emission from the applied UV source, as well as 100 muE m(-2) s(-1) white light had negligible effect. Increase in the psbD2 mRNA level was observed at very low UV-B intensities, which did not cause damage to the function and protein structure of PS II. Expression patterns of chimeric genes containing the promoter regions of the psbD1, psbD2 genes fused to the firefly luciferase (luc) reporter gene showed similar induction as observed for the endogenous psbD genes. Our findings demonstrate that UV-B radiation induces differential expression of the of the psbD1 and psbD2 genes. We propose that the primarily expressed psbD2 serves as a UV stress gene and participates in a rapid defense response against UV-B stress. This effect is regulated, at least partially, at the level of transcription.

UV-B-induced Differential Transcription of psbAGenes Encoding the D1 Protein of Photosystem II in the Cyanobacterium Synechocystis 6803

UV-B irradiation of intact Synechocystis sp. PCC 6803 cells results in the loss of photosystem II activity, which can be repaired via de novo synthesis of the D1 (and D2) reaction center subunits. In this study, we investigated the effect of UV-B irradiation on the transcription of the psbA2 and psbA3 genes encoding identical D1 proteins. We show that UV-B irradiation increases the level of psbA2 mRNA 2-3-fold and, more dramatically, it induces a 20-30-fold increase in the accumulation of the psbA3 mRNA even at levels of irradiation too low to produce losses of either photosystem II activity or D1 protein. The induction of psbA3 transcript accumulation is specific for UV-B light (290-330 nm). Low intensity UV-A emission (330-390 nm) and white light induce only a small, at most, 2-3-fold enhancement, whereas no effect of blue light was observed. Expression patterns of chimeric genes containing the promoter regions of the psbA2, psbA3 genes fused to the firefly luciferase (luc) reporter gene indicate that (i) transcription of psbA2/luc and psbA3/luc transgenes was elevated, similarly to that of the endogenous psbA genes, by UV-B irradiation, and that (ii) a short, 80-base pair psbA3 promoter fragment is sufficient to maintain UV-B-induced transcription of the luc reporter gene. Furthermore, our findings indicate that UV-B-induced expression of the psbA2 and psbA3 genes is a defense response against UV-B stress, which is regulated, at least, partially at the level of transcription and does not require active electron transport.

The UVB content of 'UVA fluorescent lamps' and its erythemal effectiveness in human skin

The UBV emission from ten different types of 'UVA fluorescent lamp' has been measured by spectroradiometry. The mean ratio of UVB emission to UVA emission was found to be 0.94+or-0.35 (1 SD)%. By weighting the spectral irradiance of each lamp by the DIN standard erythemal curve, the mean erythemally effective UVB emission (normalised to 297 nm), expressed as a percentage of the UVA emission, was 0.076+or-0.049 (1 SD)%.

Tanning, protection against sunburn and vitamin D formation with a UV-A 'sun-bed'.

There are many types of sun-beds, sun-benches and sun-panels containing fluorescent tubes which, because of their predominantly UV-A emission, are advertised to the public as a means of obtaining a tan without sunburn. This study reports the effects of a sun-bed on skin colour, on the protection afforded against sunburn, and on vitamin D formation. Side-effects are also recorded. It was shown that the sun-bed emits mainly UV-A but very little UV-B and some tanning occurred in most subjects. However, no correlation was observed between the subjects' stated ability to tan and the degree of pigmentation achieved at the end of the treatment. Most subjects also had itching and erythema, and three had polymorphic light eruption. Although very little UV-B irradiation was present, a significant increase in serum levels of 25-hydroxyvitamin D occurred, and possible explanations of this surprising finding are discussed. While the sun-bed proved popular with the subjects, only a modest tan was achieved and the incidence of side-effects appeared to limit the value of this type of appliance, especially with regard to the prevention of vitamin D deficiency.