Short-wavelength Ultraviolet Light Research Articles

Dose-dependent inactivation of Plasmodium falciparum in red blood cell concentrates by treatment with short-wavelength ultraviolet light.

Plasmodium species are naturally transmitted by Anopheles mosquitos. The parasite infects red blood cells (RBCs) and can be transfused with blood products. In non-endemic areas, the main risk of infection arises from travellers coming back and people immigrating from malaria-endemic regions. Endemic countries face a permanent risk of infection from transfusion-transmitted malaria (TTM). TTM may cause life-threatening complications in patients dependent on blood donations. This study aimed to investigate the efficacy of Plasmodium falciparum inactivation in RBC units by treatment with short-wavelength ultraviolet C (UVC) light in the absence of photochemical additives. RBC units were spiked with P. falciparum to a parasite density of 0.1%-1% and irradiated with up to 4.5 J/cm2 UVC. The parasite density of UVC-treated dilution series and untreated controls were compared over 3 weeks after irradiation. The lowest dose of 1.5 J/cm2 UVC led to a 3.1 log reduction in parasite load compared with the untreated control. The inactivation capacity was dose-dependent. Strikingly, 4.5 J/cm2 led to ≥5.3 log unit reduction, which was equivalent to a complete inactivation in two out of three experiments. Pathogen reduction with UVC light was previously shown to be effective for different bacteria and viruses, but the inactivation of parasites in RBC concentrates was not addressed until now. The present study provides evidence for significant inactivation of P. falciparum-infected RBCs by UVC light.

The dependence of light extraction improvement on optimized surface microstructure for AlGaN-based UVC-LEDs considering TM-polarized emission

In order to improve the light extraction of AlGaN-based short wavelength ultraviolet light emitting diodes (DUC-LEDs), a type of microstructure with high aspect ratio is introduced and optimized on the AlN substrate surface. And, particle swarm optimization (PSO) algorithm is used to inverse design of the surface microstructure to maximize the light extraction efficiency (LEE). Considering that the propagation characteristics of TM-polarized light are different from that of TE-polarized light, the optical field distribution and LEE is analyzed for the UVC-LEDs with different TE-polarized component when the optimized surface microstructure is applied. Furthermore, the preparation process tolerance of the high aspect ratio structure is discussed by calculating the LED's LEE when the structural deviation occurs or morphology changes. Simulation results show that, by using the optimized surface microstructure based on parabola cone array, the LEDs' LEE is increased from 4.4% to 8.7% and from 0.4% to 3.7% for TE-polarized and TM-polarized emission, respectively. In addition, it is demonstrated that the light extraction improvement by the surface microstructure has a good tolerance to the structural deviation and morphology. The results are significant for improving light extraction and realizing high efficient short wavelength AlGaN-based UVC-LEDs by designing surface microstructures.

Effect of germicidal short wavelength ultraviolet light on the polyphenols, vitamins, and microbial inactivation in a highly opaque apple juice

AbstractThe aim of this investigation was to study the efficacy of UV‐C light emitting diode (LED) system operating at 263 nm for the inactivation of Listeria monocytogenes and Escherichia coli O157:H7. UV‐C irradiation was applied to stirred 5 ml samples, using a collimated beam LED system operating at a 263 nm wavelength. UV irradiation doses ranging from 0 to 160 mJ/cm2 were also delivered to apple juice (AJ) and polyphenols and vitamins were profiled. Liquid chromatography–mass spectrometry (LC–MS/MS) analysis was conducted to assess the stability of polyphenols or vitamins in UV‐C exposed AJ. The polyphenol and vitamin results demonstrated that UV‐C irradiation in AJs at relevant commercial UV doses induced significant reductions in the concentrations of selected polyphenols and vitamins, p < .05. Ascorbic acid was reduced to 32%, at 160 mJ/cm2 whereas 17% reduction was observed at 40 mJ/cm2. Riboflavin was observed to be relatively stable. Epicatechin and chlorogenic were significantly reduced at high exposure doses. In contrast, minor changes were observed at 40 mJ/cm2. Results show that UV‐C irradiation effectively inactivated pathogenic microbes in AJ. Inactivation levels of all organisms were proportional to UV‐C dose. The log reduction kinetics of microorganisms followed log‐linear and with higher R2 (>0.95). The decimal reduction dose (D10) values of 4.16 and 3.84 mJ/cm2 were obtained from the inactivation of E. coli and L. monocytogenes in AJ. The results from this study imply that adequate log reduction of pathogens is achievable in AJ and suggests significant potential for UV‐C treatment of other opaque liquid foods.

Surface Coating- and Light-Controlled Oxygen Doping of Carbon Nanotubes

Tuning the optical properties of single-wall carbon nanotubes (SWCNTs) via oxygen doping has been a simple and effective approach to create fluorescent quantum emitters. We performed oxygen doping of SWCNTs in water utilizing chirality-pure (6,5) enantiomers with different surface coatings of DNA and surfactants by ultraviolet (UV) light irradiation. We found the reaction to be primarily dependent on the wavelength of UV light and the specific coating material on the nanotube surface. Particularly, DNA coatings react more readily with the reactive oxygen species that is photochemically produced under short-wavelength UV light than SWCNTs, preventing oxygen doping of nanotubes from occurring. The surface coverage of SWCNTs created by coating materials plays a weaker role in controlling the reaction efficiency of oxygen doping. This is demonstrated clearly by the lack of oxygen doping for two (6,5) enantiomers wrapped by DNA with drastically different surface coverages. These findings reveal important mechanisms of oxygen doping of SWCNTs, providing methods of controlling optical properties of nanotubes for developing unique applications.

The impact of far-UVC radiation (200-230 nm) on pathogens, cells, skin, and eyes - a collection and analysis of a hundred years of data.

Background: The ongoing coronavirus pandemic requires new disinfection approaches, especially for airborne viruses. The 254 nm emission of low-pressure vacuum lamps is known for its antimicrobial effect, but unfortunately, this radiation is also harmful to human cells. Some researchers published reports that short-wavelength ultraviolet light in the spectral region of 200–230 nm (far-UVC) should inactivate pathogens without harming human cells, which might be very helpful in many applications.Methods: A literature search on the impact of far-UVC radiation on pathogens, cells, skin and eyes was performed and median log-reduction doses for different pathogens and wavelengths were calculated. Observed damage to cells, skin and eyes was collected and presented in standardized form.Results: More than 100 papers on far-UVC disinfection, published within the last 100 years, were found. Far-UVC radiation, especially the 222 nm emission of KrCl excimer lamps, exhibits strong antimicrobial properties. The average necessary log-reduction doses are 1.3 times higher than with 254 nm irradiation. A dose of 100 mJ/cm2 reduces all pathogens by several orders of magnitude without harming human cells, if optical filters block emissions above 230 nm.Conclusion: The approach is very promising, especially for temporary applications, but the data is still sparse. Investigations with high far-UVC doses over a longer period of time have not yet been carried out, and there is no positive study on the impact of this radiation on human eyes. Additionally, far-UVC sources are unavailable in larger quantities. Therefore, this is not a short-term solution for the current pandemic, but may be suitable for future technological approaches for decontamination in rooms in the presence of people or for antisepsis.

Cyclometalated Iridium(III) Complexes as High-Sensitivity Two-Photon Excited Mitochondria Dyes and Near-Infrared Photodynamic Therapy Agents.

Photodynamic therapy (PDT) using two-photon near-infrared light excitation is a very effective way to avoid the use of short-wavelength ultraviolet or visible light which cannot efficiently penetrate into the biological tissues and is harmful to the healthy cells. Herein, a series of cyclometalated Ir(III) complexes with a structurally simple diimine ligand were designed and the synthetic route and preparation procedure were optimized, so that the complexes could be obtained in apparently higher yield, productivity, and efficiency in comparison to the traditional methods. Their ground state and excited singlet and triplet state properties were studied by spectroscopy and quantum chemistry theoretical calculations to investigate the effect of substituent groups on the photophysical properties of the complexes. The Ir(III) complexes, especially Ir1 and Ir3, showed very low dark toxicities and high phototoxicities under both one-photon and two-photon excitation, indicating their great potential as PDT agents. They were also found to be highly sensitive two-photon mitochondria dyes.

Chemosynthesis, characterization and application of lignin-based flocculants with tunable performance prepared by short-wavelength ultraviolet initiation

The high value utilization of lignin is facing sheer challenge, and the use of lignin as a raw material to prepare flocculants is of tremendous significance for wastewater treatment. In this study, lignin-based flocculants (LBFs) with tunable performances were prepared by mild copolymerization of lignosulfonate and [2-(Methacryloyloxy) ethyl] trimethylammonium chloride solution (METAC) under short-wavelength ultraviolet light. The effect of preparation conditions on the product performances was investigated, and two classes of LBFs were obtained in the same system by adjusting the preparation conditions. As compared with the preparation of LBFs suitable for simulated dye wastewater, higher monomer dose and lower pH were required for the preparation of LBFs suitable for kaolin and E. coli suspensions. Among them, LBF-1 could remove more than 95 % dye, and LBF-2 had 99.2 % and 97.5 % turbidity and bacterial removal rates, respectively. Moreover, the effects of external factors such as the LBF-1 dose, initial concentration of dye and wastewater pH on the decolorization efficiency were also explored. In addition, the sterilization function of LBF was studied, and LBF-2 experienced a process of first flocculation followed by sterilization. Furthermore, the flocculation mechanisms of LBFs in treating three kinds of wastewaters were discussed in detail.

Segmenting areas of potential contamination for adaptive robotic disinfection in built environments

Mass-gathering built environments such as hospitals, schools, and airports can become hot spots for pathogen transmission and exposure. Disinfection is critical for reducing infection risks and preventing outbreaks of infectious diseases. However, cleaning and disinfection are labor-intensive, time-consuming, and health-undermining, particularly during the pandemic of the coronavirus disease in 2019. To address the challenge, a novel framework is proposed in this study to enable robotic disinfection in built environments to reduce pathogen transmission and exposure. First, a simultaneous localization and mapping technique is exploited for robot navigation in built environments. Second, a deep-learning method is developed to segment and map areas of potential contamination in three dimensions based on the object affordance concept. Third, with short-wavelength ultraviolet light, the trajectories of robotic disinfection are generated to adapt to the geometries of areas of potential contamination to ensure complete and safe disinfection. Both simulations and physical experiments were conducted to validate the proposed methods, which demonstrated the feasibility of intelligent robotic disinfection and highlighted the applicability in mass-gathering built environments.

Effect of pilot-scale UV-C light treatment assisted by mild heat on E. coli, L. plantarum and S. cerevisiae inactivation in clear and turbid fruit juices. Storage study of surviving populations

Consumer growing demands for high-quality and safe food and beverages have stimulated the interest in alternative preservation technologies. Short-wavelength ultraviolet light (UV-C, 254 nm) has proven to be useful for the decontamination of a great variety of clear juices while improving their quality compared to traditional thermal treatments. Suspended solids and coloured compounds in turbid juices, diminish light transmission. The use of UV-C under a hurdle approach, may be a promising strategy for their treatment. The purpose of this study was to analyse Escherichia coli ATCC 25922, Saccharomyces cerevisiae KE 162 and Lactobacillus plantarum ATCC 8014 inactivation in clear pear juice (PJ), turbid orange-tangerine (OT) and orange-banana-mango-kiwi-strawberry (OBMKS) juices processed by single UV-C (390 mJ/cm2, 20 °C) and UV-C assisted by mild heat (UV-C/H, 50 °C) at pilot-scale in a coiled tubing unit and stored under refrigeration (5 °C). Inactivation studies were also conducted in peptone water (PW) and model solution (MS). The adequacy of the Coroller, Weibull and Biphasic Plus Shoulder models was studied. UV-C was highly effective in PW, MS and PJ, achieving up to 5.5-6.3-4.7, 4.8-5.1-4.6 and 4.4-5.5 log reductions for L. plantarum, E. coli,and S. cerevisiae, respectively. Whereas, a moderate inactivation by single UV-C was recorded in the turbid blends, reducing up to 2.4-3.8-1.6 and 3.6-3.7-1.3 log-cycles in OT and OBMKS, respectively. When the UV-C/H treatment was applied, high bacterial inactivation was observed achieving 5.2-5.6, 6.3-6.6 and 5.5-6.7 log reductions in OT, OBMKS and PJ, respectively, while 4.6-4.9 log reductions were determined for the yeast in OBMKS and OT, respectively. Thus, additive inactivation effects between UV-C and H were observed. All the models tested gave useful information regarding the existence of microbial subpopulations with varying resistances. However, the cumulative Weibull distribution function was the most versatile one, fitting inactivation curves with different shapes. Additionally, the frequency distributions of resistances showed that UV-C/H not only increased the UV-C microbicidal effect but changed the distribution of inactivation times. Principal component analysis revealed that UV-C effectiveness was associated to low particle size, a⃰, turbidity and high UV-C transmittance. An increase on the inactivation of treated bacterial populations was recorded along storage, while no yeast recovery was observed, thus emphasizing the contribution of refrigerated storage to microbial inactivation. Microbial inactivation in clear and turbid juices achieved by UV-C (390 mJ/cm2) assisted by mild heat (50 °C) and subsequent refrigerated storage may represent an useful alternative for multiple applications in the juice industry.

Enhanced UV–visible detection of InGaZnO phototransistors via CsPbBr3 quantum dots

Indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) exhibit high field-effect carrier mobility and low off-state current, which are attractive for high speed and low noise photodetectors and image sensor applications. However, with an optical band gap of ∼3.3 eV, the photodetection range of IGZO TFTs is limited to short wavelength ultraviolet (UV) light. Here, we demonstrate a simple approach to enhance the performance of IGZO-based phototransistors by incorporating layers of solution-processed perovskite quantum dots (QDs) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Owing to the fast transfer of photogenerated electrons by CsPbBr3 QDs absorbing layer, the photoresponse of QD-decorated IGZO phototransistor is extended to the visible range (500 nm), and the responsivity and detectivity of QD-decorated device are more than two order higher than those of original IGZO TFTs. Moreover, the QD-decorated IGZO phototransistor also exhibits enhanced performance under UV light (350 nm), achieving a responsivity of 9.72 A W−1, a detectivity of 2.96 × 1012 Jones, and a light to dark current ratio in the order of 106 at a wavelength of 350 nm (a light intensity of 207.3 μW cm−2).

Proof-of-principle that a decoy virus protects oncolytic measles virus against neutralizing antibodies.

BackgroundAttenuated oncolytic measles virus (OMV) is a promising antitumor agent in early-phase clinical trials. However, pre-existing immunity against measles might be a hurdle for OMV therapy.MethodsOMV was inactivated with short-wavelength ultraviolet light (UV-C). Loss of replication and oncolytic activity of UV-inactivated OMV were confirmed by tissue culture infective dose 50 (TCID50) assay using Vero cells and by flow cytometry using Jurkat cells. An enzyme-linked immunosorbent assay was performed to verify that UV-inactivated OMV remained antigenic. Different doses of UV-inactivated OMV were pre-cultured in media supplemented with measles immune serum. The mixture was transferred to Jurkat cells and active OMV was added. Active OMV-induced death of Jurkat cells was monitored by flow cytometry.ResultsUV-inactivation abrogates OMV replication while maintaining its antigenicity. UV-inactivated OMV sequesters pre-existing anti-MV antibodies in Jurkat cell culture, thereby protecting active OMV from neutralization and preserving oncolytic activity.ConclusionWe prove the principle that a non-replicating OMV can serve as a “decoy” for neutralizing anti-MV antibodies, thereby allowing antitumor activity of OMV.

Visible Light-Induced Radical Mediated DNA Damage.

Light-responsive compounds have been used to manipulate biological systems with spatial and temporal control of the event of interest. Illumination of alkylcobalamins with green light (>500nm) produces carbon-centered radicals, which have been demonstrated to effectively cause DNA damage. Molecules that cause DNA and RNA strand scission are useful for studying polynucleotide structure and the binding of small molecules and proteins to polynucleotides. Most molecules that cause DNA damage in a light-dependent manner require high energy, short wavelength ultraviolet light, which is readily absorbed by nucleotide bases causing damage to the polynucleotides. Therefore, using alkylcobalamins is advantageous for causing strand scission of polynucleotides, because they are activated by light wavelengths that are not absorbed by nucleotide bases. Green-light illumination of methylcobalamin effectively causes DNA strand scission based on gel mobility assays. This cleavage is due to the generation of carbon-centered radicals based on the results of a radical trapping study. In addition, synthesis of an alkylcobalamin with a DNA binding moiety, spermine, improves DNA cleavage efficacy by an order of magnitude in comparison with methylcobalamin.

Surprising Separation of Cannabinoid Physical Dependence and Withdrawal in an Invertebrate Model

Planarians have mammalian-like neurotransmitter systems and have been established as a novel in vivo model for neuropharmacology. In previous research, planarians that have been exposed to the cannabinoid receptor (CB-R) agonist WIN 55,212-2 for 1 h displayed abstinence-induced withdrawal when tested in drug-free, but not in drug-containing, water. The goals of the present study were to extend previous work and to further establish a cannabinoid behavioral model with planarians. The results showed 1) four different CB-R antagonists (AM251, AM281, SLV319 and SR144528) dose-relatedly blocked development of physical dependence induced by two different CB-R agonists (WIN 55,212-2 and JWH251); 2) none of the same four antagonists (AM251, AM281, SLV319 or SR144528) precipitated withdrawal; 3) short wavelength (254 nm), but not long wavelength (366 nm), ultraviolet (UV) light attenuated abstinence-induced withdrawal from WIN 55,212-2, while short wavelength UV light induced moderate withdrawal behavior. The results confirm the use of a planarian model as a simple yet robust way to study development of physical dependence to cannabinoid agonists. The effect of UV irradiation adds to the evidence that the results are receptor-related. The results also give rise to the surprising suggestion, within the limitations of the methodology, that development of cannabinoid physical dependence and antagonist-induced precipitated withdrawal might be separable phenomena in planarians.

Feasibility study of laser cooling of InF molecule

ABSTRACTBy employing ab initio quantum chemistry method, we investigate the feasibility of laser cooling InF molecule. Four low-lying electronic states (X1Σ+, C1Π, 3Π and 23Π) of InF have been calculated using the multi-reference configuration interaction (MRCI) method. The spin-orbit coupling effects are also taken into account in the electronic structure computation at the MRCI level. The highly diagonal Franck-Condon factors for C1Π → X1Σ+ transitions are estimated. The radiative lifetime of the C1Π (v′ = 0) state is about 2.22 ns, which is found to be enough short for rapid laser cooling. Though the cooling wavelength of InF is located in the short-wavelength ultraviolet light (UVC), a frequency quadrupled Ti: sapphire laser (189–235 nm) could be capable of generating laser transition wavelength of InF. Furthermore, the C1Π → X1Σ+ transitions perhaps can be followed by the B3Π1 → X1Σ+0+ transitions to attain a lower Doppler temperature. Meanwhile, for achieving quasi-closed transition cycle of InF molecule, we investigate the hyperfine structure of the lowest state X1Σ+. Overall, the present results indicate the possibility of laser cooling InF molecules.

Application of pulsed UV-irradiation and pre-coagulation to control ultrafiltration membrane fouling in the treatment of micro-polluted surface water

A major cause of ultrafiltration (UF) membrane fouling is the accumulation of microorganisms and their associated soluble products. To mitigate fouling the application of pulsed short-wavelength ultraviolet (UVC) light (around 254 nm) within the membrane tank together with pre-coagulation was investigated. In mini-pilot-scale tests carried out in parallel with conventional pre-treatment (CUF), the impact of pulsed UV (CUF-UV) at different UV irradiances and fluxes on the increase of trans-membrane pressure (TMP) was evaluated and explained in terms of the quantity and nature of membrane deposits in the membrane cake layer and pores.The results indicated that at a flux of 20 L m−2 h−1, the pulsed UV (1 min within 31 min cycle) at 3.17 × 10−2 W/cm2 prevented any measureable increase in TMP over a period of 32 days, while there was a fourfold increase in TMP for the conventional pre-treatment. For the CUF-UV system the concentration of bacteria and soluble microbial products was much less than the conventional CUF system, and the cake layer was thinner and contained less biopolymers (proteins and polysaccharides). In addition, the pores of the CUF-UV membrane appeared to have less organic deposits, and particularly fractions with a high molecular weight (>10 kDa).At a lower UV irradiance (1.08 × 10−2 W/cm2), or higher flux (40 L m−2 h−1) with the same UV irradiance, there was a measurable increase in TMP, indicating some fouling of the CUF-UV membrane, but the rate of TMP development was significantly lower (∼50%) than the conventional CUF membrane system. Overall, the results show the potential advantages of applying intermittent (pulsed) UVC irradiation with coagulation to control UF membrane fouling.

Determination of 2-alkylcyclobutanones in ultraviolet light-irradiated fatty acids, triglycerides, corn oil, and pork samples: Identifying a new source of 2-alkylcyclobutanones

Previous studies have established that 2-alkylcyclobutanones (2-ACBs) are unique radiolytic products in lipid-containing foods that could only be formed through exposure to ionizing radiation, but not by any other means of physical/heat treatment methods. Therefore, 2-ACBs are currently the marker molecules required by the European Committee for Standardization to be used to identify foods irradiated with ionizing irradiation. Using a spectrum of state-of-the-art analytical instruments, we present in this study for the first time that the generation of 2-ACBs was also possible when fatty acids and triglycerides are exposed to a non-ionizing, short-wavelength ultraviolet (UV-C) light source. An irradiation dosage-dependent formation of 2-ACBs was also observed in UV-C irradiated fatty acids, triglycerides, corn oil, and pork samples. With UV-C irradiation becoming an increasingly common food treatment procedure, it is anticipated that the results from this study will alert food scientists and regulatory officials to a potential new source for 2-ACBs.

Exposure of bovine dermal tissue to ultraviolet light under the Antarctic ozone hole

Bovine dermis was exposed outdoors in the Antarctic in 2013 to study the skin damage caused by short-wavelength ultraviolet light under the ozone hole. Collagen was extracted from the exposed dermis with pepsin. The amount of solubilized collagen in the exposed dermis was only 20%–40% of that in dermis shielded from ultraviolet light. The dermis was most difficult to extract when exposed in summer, and then when exposed in spring. Differential scanning calorimetry was used to determine the melting endothermic behavior of the dermal tissue. The peak temperature was highest for the dermis exposed in summer. The exposed dermis was degraded with cyanogen bromide to determine whether cross-linking had occurred. Cross-linked peptides were detected in the dermis exposed in summer or spring, but the dermis exposed in autumn did not differ markedly from the light-shielded dermis. These data show that cross-linkages were readily formed in the collagen molecule chains in dermis exposed to ultraviolet light in summer, when solar elevation is highest and the period of sunshine is longest. A comparison of the dermis exposed in spring and that exposed in autumn showed that cross-linkages were formed more readily by ultraviolet light in spring, when the ozone hole occurred.

Optical constants, photo-stability and photo-degradation of MB/PMMA thin films for UV sensors

The effect of different light wavelengths on methylene blue dye doped poly(methyl methacrylate) thin films during casting was investigated. The colour of the thin films which casted under the light sources of short wavelength ultraviolet light (254nm), long wavelength ultraviolet light (367nm) and sunlight were compared with the film casted in the dark. UV–vis spectrometer was used to measure the transmittance and absorbance of the fabricated films, and moreover, band gap energies were calculated. Results show that the wavelength of the applied light influences on the colour stability of methylene blue due to the photolysis of poly methyl methacrylate or chloroform (solvent). The highest decolourization rate was observed under the illumination of 254nm, in which 90% of the colour was discharged after 30min of illumination's time. However, no colour change was observed when the thin films were kept in dark during the casting step.

White-light vs. short-wavelength ultraviolet illumination of fingerprints developed with columnar thin films of Alq3

The deposition of a columnar thin film (CTF) of Alq3 on partial-bloody fingerprints has recently been shown to yield better development than many traditional development techniques. The Alq3-CTF-developed fingerprint is illuminated by short-wavelength ultraviolet (UV) light, to take advantage of the luminescence of Alq3. Experiments were undertaken to test the hypothesis that white-light illumination of Alq3-CTF-developed fingerprints is inferior to UV illumination. Objective and subjective grading of photographs of 18 Alq3-CTF-developed fingerprints on brass strongly indicate that white-light illumination is likely to be suitable for comparison; if that fails to yield a strong conclusion, then a photograph taken with short-wavelength UV illumination should be examined by a human. This procedure would reduce not only UV-induced health hazards in the laboratory but also the chance of denaturing potentially useful DNA information contained in the fingerprint.

Instability Induced by Ultraviolet Light in ZnO Thin-Film Transistors

We investigate the electrical properties of ZnO thin-film transistors (TFTs) under the ultraviolet (UV) light illumination to clarify the device reliability. The ON/OFF current ratio of ZnO TFTs shows an evident reduction due to the creation of UV photo-induced current. This behavior degradation becomes severe for devices exposed to a short-wavelength UV light. The persistent photoconductivity is observed in ZnO TFTs under the UV illumination with a much slower decay for the ON-state than the OFF-state, which is attributed to the reduced recombination under a positive gate bias. The UV light instabilities of ZnO TFTs can be explained on the basis of UV photoexcited oxygen vacancies. A feasible mechanism model is proposed in this paper. These observations and analytical model not only provide useful physical insight into the device behaviors, but also offer basic design guideline for oxide TFTs.