UV Light Emission Research Articles

Study on the synergism of steam reforming and photocatalysis for the degradation of Toluene as a tar model compound under microwave-metal discharges

The synergism of steam reforming and photocatalysis on converting the tar model compound toluene was investigated in a microwave (MW)-metal discharge reactor, using anatase TiO2 as photocatalyst and N2 and N2+Ar as carrier gas. Unlike dry-state cracking that generates noticeable soot, MW-metal discharge steam reforming can effectively eliminate soot formation and promote the conversion of toluene into permanent gases. The toluene conversion in steam reforming can be further enhanced by employing photocatalyst. However, the photocatalytic performance largely depended on the carrier gas and humidity. Compared with N2, the introduction of Ar into N2 intensified the UV light emission to trigger photocatalytic degradation of toluene. The toluene conversion efficiency under the synergetic effects of photocatalysis and steam reforming reached 98% when Ar/N2 = 1/5 (v/v) was used as the carrier gas with a moderate humidity of 38%. However, toluene was less effectively photodegraded as humidity increased high (>60%), mainly attributed to competitive adsorption between toluene and water molecules on the active sites of photocatalyst as well as the reduction in discharge intensity with humidity increase. The disclosure of the plasma and photocatalytic effects of MW-metal discharges is expected to aid further research in the field of microwave chemistry.

Near-infrared light-controlled regulation of intracellular calcium to modulate macrophage polarization

Macrophages are multifunctional immune cells with diverse physiological functions such as fighting against infection, influencing progression of pathologies, maintaining homeostasis, and regenerating tissues. Macrophages can be induced to adopt distinct polarized phenotypes, such as classically activated pro-inflammatory (M1) phenotypes or alternatively activated anti-inflammatory and pro-healing (M2), to execute diverse and dynamic immune functions. However, unbalanced polarizations of macrophage can lead to various pathologies, such as atherosclerosis, obesity, tumor, and asthma. Thus, the capability to remotely control macrophage phenotypes is important to the success of treating many pathological conditions involving macrophages. In this study, we developed an upconversion nanoparticle (UCNP)-based photoresponsive nanocarrier for near-infrared (NIR) light-mediated control of intracellular calcium levels to regulate macrophage polarization. UCNP was coated with mesoporous silica (UCNP@mSiO2), into which loaded calcium regulators that can either supply or deplete calcium ions. UCNP@mSiO2 was chemically modified through serial coupling of photocleavable linker and Arg-Gly-Asp (RGD) peptide-bearing molecular cap via cyclodextrin-adamantine host-guest complexation. The RGD-bearing cap functioned as the photolabile gating structure to control the release of calcium regulators and facilitated the cellular uptake of UCNP@mSiO2 nanocarrier. The upconverted UV light emission from the UCNP@mSiO2 under NIR light excitation triggered the cleavage of cap and intracellular release of calcium regulators, thereby allowing temporal regulation on the intracellular calcium levels. Application of NIR light through skin tissue promoted M1 or M2 polarization of macrophages, by elevating or depleting intracellular calcium levels, respectively. To the best of our knowledge, this is the first demonstration of NIR light-mediated remote control on macrophage polarization. This photoresponsive nanocarrier offers the potential to remotely manipulate in vivo immune functions, such as inflammation or tissue regeneration, via NIR light-controlled macrophage polarization.

Red and blue colours on 18th–19th century Japanese woodblock prints: In situ analyses by spectrofluorimetry and complementary non-invasive spectroscopic methods

The study of fragile artworks kept in museums requires mobile devices, short time of analysis and minimal disturbance to insure their good preservation. In situ reflectance spectroscopy and spectrofluorimetric studies are mostly developed for pigment characterization. A recently-designed μspectrofluorimeter (LED μSF) dedicated to in situ measurements, that uses UV-light emission diodes (LED) as excitation sources, was used to verify its potentiality for the identification of pigments and dyes. The colours of five Japanese woodblock prints from the Museum of Zaragoza (Spain) were studied by the combination of UV-VIS-IR spectroscopies and hand-held energy dispersive X-ray fluorescence spectrometer (HHED-XRF), together with Raman Spectroscopy. This study focused on the analysis of red and blue colours in prints by Koryūsai, Utamaro and Eisen (18th–19th centuries). The interpretation of the in situ fluorescence emission spectra could be rather difficult because of the variety of pigment mixtures, natural ageing of colorants and fluorescence of the support (paper), that could lead to spectral changes or band shifts. The combination with diffuse reflectance spectroscopy (DRS), hyperspectral imaging techniques (HSI), and HHED-XRF completed the interpretation of these results. A specific database was built analyzing reference samples made in accordance with Japanese printings techniques and materials. Inorganic and organic red (vermilion, red lead, cochineal, red safflower) and blue (Prussian blue, indigo, dayflower) pigments were used alone or as a mixture to modify the hues. The identification of Prussian blue could be a clue about the relations existing between East and West and, its presence sometimes questioned the dating of some early printings.

ФC31 Integrase-Mediated Isolation and Characterization of Novel Safe Harbors for Transgene Expression in the Pig Genome.

Programmable nucleases have allowed the rapid development of gene editing and transgenics, but the technology still suffers from the lack of predefined genetic loci for reliable transgene expression and maintenance. To address this issue, we used ФC31 integrase to navigate the porcine genome and identify the pseudo attP sites suitable as safe harbors for sustained transgene expression. The combined ФC31 integrase mRNA and an enhanced green fluorescence protein (EGFP) reporter donor were microinjected into one-cell zygotes for transgene integration. Among the resulting seven EGFP-positive piglets, two had transgene integrations at pseudo attP sites, located in an intergenic region of chromosome 1 (chr1-attP) and the 6th intron of the TRABD2A gene on chromosome 3 (chr3-attP), respectively. The integration structure was determined by TAIL-PCR and Southern blotting. Primary fibroblast cells were isolated from the two piglets and examined using fluorescence-activated cell sorting (FACS) and enzyme-linked immunosorbent assay (ELISA), which demonstrated that the chr1-attP site was more potent than chr3-attP site in supporting the EGFP expression. Both piglets had green feet under the emission of UV light, and pelleted primary fibroblast cells were green-colored under natural light, corroborating that the two pseudo attP sites are beneficial to transgene expression. The discovery of these two novel safe harbors for robust and durable transgene expression will greatly facilitate the use of transgenic pigs for basic, biomedical and agricultural studies and applications.

A NIR-responsive azobenzene-based supramolecular hydrogel using upconverting nanoparticles

To circumvent the need for direct UV excitation in a supramolecular hydrogel composed of an azobenzene-modified poly(acrylic acid) copolymer and deoxycholate-β-cyclodextrin as a crosslinker, we modified this system for use with LiYF4:Tm3+/Yb3+ upconverting nanoparticles, which emit UV light upon NIR excitation. A complete gel-sol transition was observed in 60 minutes upon 980 nm irradiation. No change was observed under similar conditions of a control sample over the same period of time.

A versatile approach to synthesise optically active hierarchical ZnS/ZnO heterostructures

One-dimensional hierarchical ZnS/ZnO heterostructures have been successfully fabricated by combining thermal evaporation method and in-situ/post oxidation process. Various morphologies of the secondary ZnO nanostructures such as nanosheets, nanoparticles, and nanoteeths were found to form on the ZnS nanowire backbone. The optical properties of the heterostructures were investigated by high-spatial resolution cathodoluminescence spectroscopy. It was demonstrated that optically active hierarchical ZnS/ZnO heterostructures, which strongly emit UV light with two emission bands at around 335 nm and 380 nm characterising both the ZnS and the ZnO phases, can be realised by controlling the oxidation temperature and duration. This research introduces a simple route to synthesise optically active ZnS/ZnO heterostructures.

Study on electrical structure and magneto-optical properties of W-doped ZnO

For W-doping amounts ranging from 0.0417 to 0.0833, experimental UV–visible absorption spectra blue shift and red shift results have been reported in the literatures. However, there is few literature reported research on magnetic mechanism. To solve this problem, this study investigates the disagreement about blue shift and red shift results and research on magnetic mechanism. The band structures, density of states, absorption spectra and magnetism have been investigated using first-principles planewave ultrasoft pseudopotential method based on the density functional theory. The calculated results showed that increased W-doping amounts first increase the volumes, and then reduce the volumes, decrease the formation energies, and stabilize the doped system. The band gaps become narrower and the absorption spectrum exhibits a significant red shift in UV and visible light emission. Moreover, the covalent bond vertical to c-axis strengthens, and the ionic bond parallel to c-axis weakens. Increased W-doping amounts decrease the magnetism of doped system. The magnetism of doped system originates from the electron exchange among W-5d, O-2p and Zn-3d orbitals of the W-doped ZnO. In W double-doped system, the ferromagnetic Curie temperature can be above room temperature when the doped system has a longer W-W distance.

Dye-modified ZnO nanohybrids: optical properties of the potential solar cell nanocomposites

We report the hybridization of ZnO with natural dyes [Laali, Zobo] or synthetic dye [methyl red] forming ZnO–laali, ZnO–zobo and ZnO–methyl red nanocomposites in bright colours. The structural, optical and dye photosensitization influence of the hybrid nanocomposites were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–Visible absorption spectroscopy and photoluminescence (PL). The surface plasmon absorption band of ZnO–laali and ZnO–zobo shifts towards red and blue, respectively, with significantly enhanced absorption intensities, indicating the interaction and optical influence of the respective dyes in photosensitization. Optical and absorption character of ZnO methyl red and bare ZnO are similar indicating the insignificant effect of methyl red on photosensitization. PL spectra of ZnO–laali and ZnO–zobo display enhanced UV light emission due not only to the surface electron transfer from their respective inherent isoplumbagin and anthocyanin to ZnO but also to the extension of the Fermi energy level to the ZnO. Dyes adopted influence the optical band gaps of the evolved hybrid nanocomposites.

Minimizing the Heat Effect of Photodynamic Therapy Based on Inorganic Nanocomposites Mediated by 808 nm Near-Infrared Light.

Photodynamic therapy (PDT) based on photosensitizers (PSs) constructed with nanomaterials has become popular in cancer treatment, especially oral carcinoma cell. This therapy is characterized by improved PS accumulation in tumor regions and generation of reactive oxygen species (ROS) for PDT under specific excitation. In the selection of near-infrared (NIR) window, 808 nm NIR light because it can avoid the absorption of water is particularly suitable for the application in PDT. Hence, multiband emissions under a single 808 nm near-infrared excitation of Nd3+ -sensitized upconversion nanoparticles (808 nm UCNPs) have been applied for the PDT effect. 808 nm UCNPs serve as light converter to emit UV light to excite inorganic PS, graphitic carbon nitride quantum dots (CNQDs), thereby generating ROS. In this study, a nanocomposite consisting UCNPs conjugated with poly-l-lysine (PLL) to improve binding with CNQDs is fabricated. According to the research results, NIR-triggered nanocomposites of 808 nm UCNP-PLL@CNs have been verified by significant improvement in ROS generation. Consequently, 808 nm UCNP-PLL@CNs exhibit high capability for ROS production and efficient PDT in vitro and in vivo. Moreover, the mechanism of PDT treatment by 808 nm UCNP-PLL@CNs is evaluated using the cell apoptosis pathway.

Energy down converting organic fluorophore functionalized mesoporous silica hybrids for monolith-coated light emitting diodes

The covalent attachment of organic fluorophores in mesoporous silica matrices for usage as energy down converting phosphors without employing inorganic transition or rare earth metals is reported in this article. Triethoxysilylpropyl-substituted derivatives of the blue emitting perylene, green emitting benzofurazane, and red emitting Nile red were synthesized and applied in the synthesis of mesoporous hybrid materials by postsynthetic grafting to commercially available MCM-41. These individually dye-functionalized hybrid materials are mixed in variable ratios to furnish a powder capable of emitting white light with CIE chromaticity coordinates of x = 0.33, y = 0.33 and an external quantum yield of 4.6% upon irradiation at 410 nm. Furthermore, as a proof of concept two different device setups of commercially available UV light emitting diodes, are coated with silica monoliths containing the three triethoxysilylpropyl-substituted fluorophore derivatives. These coatings are able to convert the emitted UV light into light with correlated color temperatures of very cold white (41100 K, 10700 K) as well as a greenish white emission with correlated color temperatures of about 5500 K.

A two-pronged strategy to enhance visible-light-driven overall water splitting via visible-to-ultraviolet upconversion coupling with hydrogen-oxygen recombination inhibition

Visible-light-driven overall splitting water is a potential and sustainable approach for hydrogen generation. Although many photocatalysts have been reported to be active for this reaction, the efficiency of overall splitting water is still quite low. In this work, a two-pronged strategy is adopted to overcome two key restrictions on visible-light-driven photocatalytic overall water splitting by taking advantages of visible-to-ultraviolet upconversion (UC) effect as well as inhibiting hydrogen-oxygen recombination reaction over the photocatalyst. In order to realize that purpose, a composite photocatalyst with high stability was designed by assembling three components consisting of visible-to-ultraviolet UC Pr3+-Y2SiO5, UV-responsive semiconductor photocatalyst CaTiO3 and perfluorodecalin as an oxygen transfer regent. By the first strategy, the visible-to-ultraviolet UC unit is capable of converting visible irradiation to UV light emission, which effectively excites UV-responsive photocatalyst CaTiO3. The photocatalytic activity has been raised up to 200% by regulating the amount of visible-to-ultraviolet UC Pr3+-Y2SiO5 in the designed composite photocatalyst Pr3+-Y2SiO5/CaTiO3. The photocatalyst exhibited high photochemical stability and catalytic stability in four recycle reactions. By the second strategy, hydrogen and oxygen recombination on photocatalyst surface has been effectively inhibited by an oxygen transfer reagent FDC to capture and take away newly generated oxygen from catalyst surface. This two-pronged strategy is not only convenient and efficient, but exhibits potential versatility for the most stable UV-responsive semiconductor photocatalysts to realize overall split water by visible light irradiation.

Thermal stability of UV light emitting boron nitride nanowalls

Thermal stability of the boron nitride nanowalls (BNNWs) obtained by plasma-enhanced chemical vapor deposition (PECVD) from borazine (B3N3H6), in oxidative (air) and inert (argon) atmospheres was studied. The annealing caused the sample surface oxidation with the replacement of nitrogen atoms by oxygen in the hexagonal h-BN structure, which led to a destruction of the layered structure. Strong UV light emission with a broad band ranging from 300 to 500nm at room temperature was detected. Changes in composition, morphology, structure and luminescent properties of the samples before and after annealing in different atmospheres are reported. The BNNWs obtained at 700°C from B3N3H6-NH3 mixture were stable at the temperatures up to 1100°C and improved their luminescence properties after annealing. Due to high thermal stability and luminescence the present BNNWs may find applications in the optical devices operating at high temperatures.

Correction to "Modeling the Radical Chemistry in an Oxidation Flow Reactor: Radical Formation and Recycling, Sensitivities, and the OH Exposure Estimation Equation".

Oxidation flow reactors (OFRs) containing low-pressure mercury (Hg) lamps that emit UV light at both 185 and 254 nm (“OFR185”) to generate OH radicals and O3 are used in many areas of atmospheric science and in pollution control devices. The widely used potential aerosol mass (PAM) OFR was designed for studies on the formation and oxidation of secondary organic aerosols (SOA), allowing for a wide range of oxidant exposures and short experiment duration with reduced wall loss effects. Although fundamental photochemical and kinetic data applicable to these reactors are available, the radical chemistry and its sensitivities have not been modeled in detail before; thus, experimental verification of our understanding of this chemistry has been very limited. To better understand the chemistry in the OFR185, a model has been developed to simulate the formation, recycling, and destruction of radicals and to allow the quantification of OH exposure (OHexp) in the reactor and its sensitivities. The model outputs of ...

Application of porous silicon microcavity to enhance photoluminescence of ZnO/PS nanocomposites in UV light emission

This paper presents ZnO nanostructures deposited on porous silicon (PS) and porous silicon microcavity (PSM) substrates by sol-gel method. The effects of annealing temperature and mass ration of zinc acetate to PVA on microstructure, and optical properties of ZnO/PS and ZnO/PSM nanocomposites were systematically investigated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The XRD analysis confirmed that the ZnO/PS nanocomposite preferred strongly to (002) phase orientation. The PL spectra showed that there was a sharp and highly intense UV emission peak located at about 400nm when annealing temperature was 800°C for 30min and the mass ratio of zinc acetate to PVA was 4:1. The detail cross-section FESEM images of ZnO/PSM showed that ZnO nanoparticles uniformly penetrated into all PS layers and adhered to them very well. Furthermore, ZnO/PSM nanocomposites showed relatively stronger UV emissions at around 400nm compared to the PL spectra of ZnO/PS nanocomposites, that means one-dimension phonic crystal PSM can enhance the PL intensity of ZnO. Such a method may provide an interesting way to develop a new type of UV optoelectronic devices.

Insight of dipole surface plasmon mediated optoelectronic property tuning of ZnO thin films using Au

Surface plasmon mediated photoluminescence (PL) studies of ZnO, ZnO/Au, ZnO/Au/ZnO and Au/ZnO films have been investigated. An enhancement of UV and visible light emission has been observed in ZnO/Au and ZnO/Au/ZnO films, compared to that of ZnO thin films, while for Au/ZnO films quenching of PL intensity was observed. Excitation intensity (EI) dependent PL spectra have shown dominance of horizontal dipole surface plasmon mode for ZnO/Au/ZnO, ZnO/Au samples, which led enhanced greenish-yellow and orange emissions respectively. Moreover, confocal laser scanning microscope measurements and diffuse reflectance spectroscopy were conducted to investigate the mechanism behind the variations and involvement of Urbach tail. UV and visible region absorption were selectively enhanced by varying the Au and ZnO configuration and can be assigned to the interaction of the dipole surface plasmon resonance with localized trapping levels and phonon subsystem. The excellent photoluminescence performance has immense potential for ZnO thin film based optoelectronic devices.

CeF3-ZnO scintillating nanocomposite for self-lighted photodynamic therapy of cancer.

We report on the synthesis and characterization of a composite nanostructure based on the coupling of cerium fluoride (CeF3) and zinc oxide (ZnO) for applications in self-lighted photodynamic therapy. Self-lighted photodynamic therapy is a novel approach for the treatment of deep cancers by low doses of X-rays. CeF3 is an efficient scintillator: when illuminated by X-rays it emits UV light by fluorescence at 325 nm. In this work, we simulate this effect by exciting directly CeF3 fluorescence by UV radiation. ZnO is photo-activated in cascade, to produce reactive oxygen species. This effect was recently demonstrated in a physical mixture of distinct nanoparticles of CeF3 and ZnO [Radiat. Meas. (2013) 59:139-143]. Oxide surface provides a platform for rational functionalization, e.g., by targeting molecules for specific tumors. Our composite nanostructure is stable in aqueous media with excellent optical coupling between the two components; we characterize its uptake and its good cell viability, with very low intrinsic cytotoxicity in dark.

Photodegradation of the UV filter ethylhexyl methoxycinnamate under ultraviolet light: Identification and in silico assessment of photo-transformation products in the context of grey water reuse

To prevent water shortages in the future and to reduce domestic water consumption, decentralized grey water (GW) reuse has become increasingly important. This water has, however, to be free of pollutants. Conventional treatment of GW does not fully eliminate micropollutants such as the UV filter substance ethylhexyl methoxycinnamate (EHMC). EHMC, which is commonly used in sunscreens and personal care products, is an endocrine disruptor and shows potential to bioaccumulation, which is also reflected in its low water solubility. Photolysis has been proposed as an alternative treatment method for other micropollutants, but it is not clear yet whether it can also be used to eliminate EHMC. One goal of this study was to better understand the basic pathways involved in this process. It aimed to identify photo-transformation products (photo-TPs) by using, in the test conditions, an initial concentration of EHMC higher than those expected in the environment. Acetonitrile (ACN) was added in low concentrations to the aqueous solution to overcome the low aquatic solubility of EHMC. The influence of this co-solvent on the degradation kinetics was studied. The photolysis experiments were carried out using a medium pressure mercury lamp, which emits UV light in the range of 200–400nm. The quantum yield of the photolysis of EHMC was 0.0042 and 0.0023mol·Einstein−1 (for 0.2 and 0.5% ACN (v/v), respectively), and the relative and absolute UV photon fluxes were determined. HPLC was used to monitor the elimination kinetics of EHMC, which followed first-order kinetics. The results of LC-MSn analyses revealed that beside others, several oxidized and hydroxylized EHMC isomers were formed as photo-TPs in aqueous solution. Using a set of in silico quantitative structure-activity relationship (QSAR) models, this study also offered new insights concerning the environmental fate and toxicity of the TPs of EHMC.

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

ZnO is an efficient luminescent material in the UV-range ∼3.4 eV with a wide range of applications in optical technologies. Sputtering is a cost-effective and relatively straightforward growth technique for ZnO films; however, most as-grown films are observed to contain intrinsic defects which can significantly diminish the desirable UV-emission. In this research the defect dynamics and optical properties of ZnO sputtered films were studied via post-growth annealing in Ar or O2 ambient, with X-ray diffraction (XRD), imaging, transmission and Urbach analysis, Raman scattering, and photoluminescence (PL). The imaging, XRD, Raman and Urbach analyses indicate significant improvement in crystal morphology and band-edge characteristics upon annealing, which is nearly independent of the annealing environment. The native defects specific to the as-grown films, which were analyzed via PL, are assigned to Zni related centers that luminesce at 2.8 eV. Their presence is attributed to the nature of the sputtering growth technique, which supports Zn-rich growth conditions. After annealing, in either environment the 2.8 eV center diminished accompanied by morphology improvement, and the desirable UV-PL significantly increased. The O2 ambient was found to introduce nominal Oi centers while the Ar ambient was found to be the ideal environment for the enhancement of the UV-light emission: an enhancement of ∼40 times was achieved. The increase in the UV-PL is attributed to the reduction of Zni-related defects, the presence of which in ZnO provides a competing route to the UV emission. Also, the effect of the annealing was to decrease the compressive stress in the films. Finally, the dominant UV-PL at the cold temperature regime is attributed to luminescent centers not associated with the usual excitons of ZnO, but rather to structural defects.

Thermotropic liquid–crystalline properties of 4,4′-dialkoxy-3,3′-diaminobiphenyl compounds and their precursors

ABSTRACTA series of 4,4ʹ-dialkoxy-3,3ʹ-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, 1H and 13C spectroscopy and elemental analysis. Their thermotropic liquid–crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4ʹ-dialkoxy-3,3ʹ-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3ʹ-diaminobiphenyl derivatives having flexible alkyl chains (C6–C12) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3ʹ-dinitrobiphenyl derivatives containing alkyl chains C7, and C9–C11 exhibit the SmA phase, those containing C8 formed the smectic C (SmC) phase and C12 formed both the SmA and smectic B (SmB) phases, respectively. The 3,3ʹ-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237–329°C, while those of 3,3ʹ-dinitrobiphenyl derivatives were in the temperature range of 270–321°C. The 3,3ʹ-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile.

9,10-diphenylanthracene (DPA) single crystals grown by conventional slow evaporation method and its characterisation

Single crystals of 9,10-diphenylanthracene (DPA) were grown by slow evaporation solution growth technique. The grown crystal was confirmed by single crystal. Powder X-ray diffraction was carried out to confirm the crystallinity of the grown crystal. The percentage of transmittance and lower cut-off wavelength was identified from UV–vis–NIR studies. The thermal characteristics of DPA were analysed by thermogravimetric (TG) and differential thermal analysis (DTA). The mechanical stability of DPA crystal was analysed by Vicker’s hardness test. The refractive index of DPA crystal was found to be 1.652. Photoluminescence studies reveal that the DPA crystal exhibits UV light emission. The third-order nonlinear optical property of DPA crystal was analysed through Z-scan technique using He–Ne laser at the wavelength of 632.8 nm. The laser damage threshold value of DPA is found to be 2.18 GW/cm2.