Realization of high-efficiency AlGaN deep ultraviolet light-emitting diodes with polarization-induced doping of the p-AlGaN hole injection layer

We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.

240 nm AlGaN-based deep ultraviolet micro-LEDs:size effect versus edge effect

240 nm AlGaN-based micro-LEDs with different sizes are designed and fabricated.Then,the external quantum efficiency(EQE)and light extraction efficiency(LEE)are systematically investigated by comparing size and edge effects.Here,it is revealed that the peak optical output power increases by 81.83%with the size shrinking from 50.0 to 25.0μm.Thereinto,the LEE increases by 26.21%and the LEE enhancement mainly comes from the sidewall light extraction.Most notably,transversemagnetic(TM)mode light intensifies faster as the size shrinks due to the tilted mesa side-wall and Al reflector design.However,when it turns to 12.5μm sized micro-LEDs,the output power is lower than 25.0μm sized ones.The underlying mechanism is that even though protected by SiO2 passivation,the edge effect which leads to current leakage and Shockley-Read-Hall(SRH)recombination deteriorates rapidly with the size further shrinking.Moreover,the ratio of the p-contact area to mesa area is much lower,which deteriorates the p-type current spreading at the mesa edge.These findings show a role of thumb for the design of high efficiency micro-LEDs with wavelength below 250 nm,which will pave the way for wide applications of deep ultraviolet(DUV)micro-LEDs.

Ultraviolet light exposure and its penetrance through the eye in a porcine model

AIM:To determine the amount of ultraviolet(UV)light irradiance that various layers of the eye receive as sunlight passes through the eye,and to investigate the protective benefits of UV light-blocking contact lenses.METHODS:Twenty-four porcine eyes were prepared in one of three ways:isolated cornea,cornea and lens together,or whole eye preparation.UV light irradiance was measured with a UV-A/B light meter before and after the eye preparations were placed over the meter to measure UV light penetration in each eye structure.In the whole eye preparation,a hole was placed in the fovea to measure light as it passed through the vitreous.Subsequently,UVprotective contact lenses were placed over the structures,and UV light penetrance was measured.Measurements of UV light exposure were taken outdoors at various locations and times.RESULTS:Cornea absorbed 63.56%of UV light that reached the eye.Cornea and lens absorbed 99.34%of UV light.Whole eye absorbed 99.77%of UV light.When UV-protective contact lenses were placed,absorption was 98.90%,99.55%,and 99.87%,respectively.UV light exposure was dependent on directionality and time of day,and was greatest in areas of high albedo that reflect significant amounts of light,such as a beach.CONCLUSION:Cornea absorbs the majority of UV light that reaches the eye in this model.UV-protective contact lenses reduce UV exposure to the eye.Locations with high albedo expose the eye to higher levels of UV light.

Novel Low Viscosity Zinc Oxide, Iron Oxides and Erioglaucine Sunscreen Potential to Protect from Ultraviolet, Visible Light and Near-Infrared Radiation

Despite the widespread recommendation and use of sunscreens and ultraviolet blocking materials, solar-induced skin damage and photoageing continues to pose a problem to human health worldwide. We have previously reported that solar visible light and near-infrared also contribute to skin damage and photo ageing. Most commonly recommended sunscreens are only effective throughout the UV spectrum, offering no protection from visible light and near-infrared. A possible solution could be to augment sunscreens with metal oxides which block visible light and near-infrared radiation. To evaluate the enhanced solar-spectrum blocking ability of novel low viscosity sunscreen containing zinc and iron oxides, a double-beam spectrophotometer was used to optically measure the transmission spectra. The spectrophotometer deploys a unique, single monochromatic design to detect wavelength penetration in the range of 240 to 2600 nm. The Sunscreen base without zinc oxide and iron oxides (control) blocked over 80% of ultraviolet-C and ultraviolet-B but did not block ultraviolet-A, visible light, or near-infrared. The novel low viscosity zinc oxide sample blocked almost over 90% ultraviolet, but did not block visible light and near-infrared sufficiently. However, the samples with the novel low viscosity zinc oxide, iron oxides and erioglaucine blocked almost over 90% of ultraviolet, visible light and near-infrared. It can be concluded that this novel combination of low viscosity zinc oxide, iron oxides and erioglaucine is effective at blocking ultraviolet, visible light and near-infrared radiation. The results of this study imply that sunscreens that provide comprehensive photoprotection from ultraviolet through to near-infrared should be adopted to prevent skin photodamage.

Photoprotective Ability of Colored Iron Oxides in Tinted Sunscreens against Ultraviolet, Visible Light and Near-Infrared Radiation

Solar-induced skin damage continues to pose a problem to human health worldwide, despite the widespread recommendation and use of sunscreens. We have previously reported that solar visible light and near-infrared also contribute to skin damage and photoageing. Most commonly recommended sunscreens are only effective throughout the UV spectrum, offering no protection from visible light and near-infrared. To evaluate the enhanced solar-spectrum blocking ability of iron oxides, a double-beam spectrophotometer was used to optically measure the transmission spectra. The spectrophotometer deploys a unique, single monochromatic design to detect wavelength penetration in the range of 240 to 2600 nm. The sample without iron oxide (control) blocked over 80% of ultraviolet-C and ultraviolet-B but did not block ultraviolet-A, visible light, or near-infrared wavelengths. The samples with yellow, and red iron oxide blocked over 90% ultraviolet, but did not block visible light and near-infrared effectively. The sample with black iron oxide blocked visible light, and near-infrared effectively compared with other samples with yellow, blue, and red iron oxide. The sample with red and black iron oxides, and the sample with yellow, blue, red, and black iron oxides blocked ultraviolet through to near-infrared. It can be concluded that dark colored iron oxide combinations are effective at blocking from ultraviolet through to visible light and near-infrared radiation. The results of this study may also suggest that biological colour of human skin and subcutaneous tissues are conserved for comprehensive photoprotection.

Photoprotective Ability of Sunscreens against Ultraviolet, Visible Light and Near-Infrared Radiation

Despite the widespread prevalence of daily sunscreen usage, solar-induced skin damage continues to occur. We have previously reported that solar visible light and near-infrared, in addition to ultraviolet radiation, perform as aging factors and induce deleterious effects such as photoaging, vasodilation, muscle thinning, skin ptosis, photoimmunosupression and photocarcinogenesis. Despite this, most commonly used sunscreens only block ultraviolet radiation. To evaluate the complete solar-spectrum blocking ability of sunscreens produced by internationally well-known companies, a double-beam spectrophotometer was used to optically measure the transmission spectra. The spectrophotometer utilizes a unique, single monochromatic design covering a wavelength range of 240 to 2600 nm. Sunscreens (thickness, 0.1 mm, SPF50+, PA+++ or ++++) from internationally well-known companies blocked 78.8% - 99.9% of ultraviolet, 33.4% - 99.6% of visible light, and 27.0% - 76.4% of near-infrared. It can be concluded that while most commercially available sunscreens filter ultraviolet radiation, they are not effective at blocking visible light and near-infrared radiation. The results of this study imply that sunscreens that provide comprehensive photoprotection from ultraviolet through to near-infrared should be considered to prevent skin photodamage.

Effect of Ultraviolet Radiation on Hsp70 Protein Expression in HaCaT Cells

Ultraviolet radiation by its wavelength is divided into: UVA, UVB and UVC. Only UVA and UVB manage to penetrate the ozone layer, but due to anthropological activities, all of them are capable of interacting with humans to a greater or lesser extent, and can generate adverse effects such as cellular stress when interacting with intra-and extracellular biomolecules. The skin is the first organ in contact with UV radiation, and the stress it generates can be analyzed by the expression of a bioindicator of cellular damage such as Hsp70. Therefore, the objective of the project was: to determine the effect of UVA, UVB and UVC radiation on HaCaT epithelial cells, by analyzing the expression of Hsp70. Materials and methods: HaCaT cells were cultured in vitro, which were irradiated with UVA, UVB and UVC light at different doses, to subsequently determine the degree of Hsp70 expression by Immunodetection by PAGE-SDS and Western Blot. Results: Basal expression of Hsp70 was observed in no irradiated HaCaT cells. When HaCaT cells were irradiated with UVA, UVB, UVC, an increase in this Hsp70 protein was observed. With UVA, a higher degree of expression was observed at a time of 30 minutes of irradiation. With UVB the highest expression shifted to a time of 20 minutes. With UVC, overexpression was observed after 10 minutes. Conclusion: UV radiation generates cellular stress on HaCaT cells, evaluated by the stress bioindicator Hsp70. According to the wavelength of UV radiation, those that have a shorter wavelength have a greater potential for cellular damage, such as UVC.

Research on the Performance of Non-Line-of-Sight Ultraviolet Communication in Rain and Fog Environment

Wireless ultraviolet communication is a new type of communication mode. It refers to the transmission of information through the scattering of ultraviolet light by atmospheric particles and aerosol particles. The scattering characteristics can enable the wireless ultraviolet communication system to transmit ultraviolet light signals in a non-line-of-sight manner, which overcomes the weakness that other free space optical communications must work in a line-of-sight manner. Based on the basic theory of scattering and absorption in atmospheric optics, taking the ultraviolet light with a wavelength of 266 nm as an example, this paper introduces the classical model of non-line-of-sight single-scattering coplanarity based on the ellipsoid coordinate system. The model is used to simulate and analyze the relationship between the geometric parameters such as transmission distance, transceiver elevation angle and transceiver half-angle and the received optical power per unit area. The performance of non-line-of-sight ultraviolet communication system in rain and fog environment is discussed respectively. The results show that the transmission quality of non-line-of-sight ultraviolet atmospheric propagation is greatly affected by the communication distance. As the distance increases, the received light power per unit area gradually decreases. In addition, increasing the emission elevation angle, the receiving elevation angle and the receiving half angle is an important way to improve the system performance.

Research on Effect of Four Natural Ultraviolet Light Absorbers on Photostabilization of Azadirachtin-A

This study examined the photostabilization of Azadirachtin-A （Aza-A） when exposed to ultraviolet light in the presence of some natural absorbers. Aza-A extract solutions with and without natural UV light absorbers in methanol were applied onto the surface of glass slides. At particular intervals, the remaining concentration of Aza-A was analyzed by HPLC. Using first-order kinetic equation, the dissipation half-life values （DT^0） for the degradation of Aza-A under ultraviolet radiation were obtained. It indicated that the addition of ferulic acid, gallic acid, and rutin provided moderate degree of photostabilization of Aza-A and that addition of aloin provided the best photostabilization of Aza-A, among these UV absorbers studied. Photostabilization of Aza-A by different UV light absorbers appears to be due to the competitive energy absorption of UV photons by the absorbers molecules. The dissipation half-life values of Aza-A after irradiation under ultraviolet light suggested that the addition of aloin （in 1 ： 1 mol ratio） can provide better photostabilization of azadirachtin molecule.

A 10×10 deep ultraviolet light-emitting micro-LED array

In this work,we design and fabricate a deep ultraviolet(DUV)light-emitting array consisting of 10×10 micro-LEDs(μ-LEDs)with each device having 20μm in diameter.Strikingly,the array demonstrates a significant enhancement of total light output power by nearly 52%at the injection current of 100 mA,in comparison to a conventional large LED chip whose emitting area is the same as the array.A much higher(~22%)peak external quantum efficiency,as well as a smaller efficiency droop forμ-LED array,was also achieved.The numerical calculation reveals that the performance boost can be attributed to the higher light extraction efficiency at the edge of eachμ-LED.Additionally,the far-field pattern measurement shows that theμ-LED array possesses a better forward directionality of emission.These findings shed light on the enhancement of the DUV LEDs performance and provide new insights in controlling the light behavior of theμ-LEDs.

Effect of Pulsed Ultraviolet Light on the Total Phenol Content of Elderberry (<i>Sambucus nigra</i>) Fruit

The changes in total polyphenolics in elderberry (Sambucus nigra) following treatment with various doses of pulsed ultraviolet rays (UV) were investigated. Four pulsed UV durations (5, 10, 20, 30 seconds) at three energy dosages (4500, 6000, 11,000 J/m2/pulse) were considered for the research. All treated elderberry fruits were incubated for 24 h at room temperature (25℃) following treatment to ensure enough response duration for enhanced development of polyphenols by the berries. The highest increase in total phenolics around 50% was found with 11,000 J/m2/pulse for a 10 seconds treatment while nearly 40% increase in total phenolics was found at an energy dosage of 11,000 J/m2/pulse after 5 seconds exposure. Even though most of the treatments indicated an increase in total polyphenols, some treatment expressed a decrease in phenolics content when compared to untreated fruits.

Performance improvement of AlGaN-based deep ultraviolet light-emitting diodes with double electron blocking layers

The AlGaN-based deep ultraviolet light-emitting diodes（LED） with double electron blocking layers（d-EBLs） on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency（IQE）. The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells（QWs） enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.

Efficiency enhancement of ultraviolet light-emitting diodes with segmentally graded p-type AlGaN layer

AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.

Studies on the oxidative modification of low density lipoprotein induced by ultraviolet light and the protective effect of green tea polyphenols

Uitraviolet（UV）light irradiation acting on human low density lipoprotein（LDL）couldgive rise to oxidative modification of LDL.Thiobarbituric acid reactive substances（TBARS）,rela-five electrophorefic mobility（REM）,relative fluorescence intensity at 420 nm（the excitation wavelength was 360nm）and lipid conjugated dienes of UV-irradiated LDL were all elevated withthe increase of irradiation time.Addition of 0.01％ EDTA into the irradiation system could inhi-bit this reaction,but the effect was not so potent as that induced in the Cu2+-PBS-LDLoxidative modification system China green tea polyphenols（CGTP）,on the other hand,had aneffective inhibitory effect with obvious dose-effect relationship.It was proposed that lipidperoxidation of LDL induced by free radicals which were generated from UV-irradiation andthe inhibitory effect of CGTP was attributed to its strong antioxidative action.

Determination of Thioglucoside in Cabbage by Using the Ultraviolet-visible Light Spectrophotometer

The ultraviolet-visible light spectrophotometer method was adopted to determine thioglucoside in cabbage with the seeds.Individual plant of cabbage was used as test materials,palladium chloride as complexing agent and sodium cellulose glycolate as dispersing agent.The results showed that palladiumd thioglucoside method could be taken as a quick,easy and precise quantitative analysis method to determine thioglucoside in cabbage.

Measurement and analysis of ozone, ultraviolet B and aerosol light scattering coefficients in the Arctic

Tropospheric ozone （O3）, ultraviolet B （UVB） radiation and aerosol light scattering coefficients （SC） were investigated on a cruise ship during the fourth Chinese National Arctic Research Expedition from July 1 September 20, 2010. The results showed that O3, UVB and SC decreased with increasing latitude, with minimum values recorded in the central Arctic Ocean. Average O3 concentrations were 15.9 ppbv and 15.1 ppbv in the Bering Sea and Arctic Ocean, respectively. Ozone concentrations increased to 17.5 ppbv in the high Arctic region. Average UVB values were 0.26 W.m-2 and 0.14 W.m-2 in the Bering Sea and Arctic Ocean, respectively. The average SC in the Bering Sea was 4.3 M.m-1, more than twice the value measured in the Arctic Ocean, which had an average value of 1.7 M.m-1. Overall, UVB and SC values were stable in the central Arctic Ocean.

Antibiotic Bone Cement and Ultraviolet Light Use in Total Knee Arthroplasty

Objective: The purpose of this study was to determine usefulness of antibiotic bone cement and UV light in primary Total Knee Arthroplasty (TKA). Patients and Methods: Between 1986 and 2008, 3105 TKAs were performed using 750 mg of cefuroxime per bag of cement (Group 1), 7537 using cefuroxime and UV light (Group 2), and 4573 using UV light and gentamicin premixed (Group 3). Results: The primary infection rate was 0.57% (87 acute postoperative infections). Of these, 27 (0.9%) were in Group 1, 44 (0.6%) were in Group 2, and 16 (0.35%) were in Group 3 (p = 0.0013). Kaplan-Meier survival in Groups 1 - 3 for reoperation for aseptic loosening of any component at 5 years was 0.9908, 0.9927, and 0.9959, respectively (p = 0.1315). Conclusion: Despite potential concerns mentioned in the literature, these results continue to support the use of antibiotic bone cement and UV lights during TKA.

Enhanced performance of AlGaN-based ultraviolet light-emitting diodes with linearly graded AlGaN inserting layer in electron blocking layer

The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.

ZnO-based deep-ultraviolet light-emitting devices

Deep-ultraviolet（DUV） light-emitting devices（LEDs） have a variety of potential applications.Zinc-oxide-based materials,which have wide bandgap and large exciton binding energy,have potential applications in high-performance DUV LEDs.To realize such optoelectronic devices,the modulation of the bandgap is required.This has been demonstrated by the developments of Mg_xZn_（1-x）O and Be_xZn_（1-x）O alloys for the larger bandgap materials.Many efforts have been made to obtain DUV LEDs,and promising successes have been achieved continuously.In this article,we review the recent progress of and problems encountered in the research of ZnO-based DUV LEDs.