UV Transparent Materials Research Articles

High-pressure synthesis and crystal structure analysis of PbTeO4, a UV transparent material.

Using the additional parameter pressure (Walker-type multianvil device), the lead(II) oxidotellurate(VI) PbTeO4 was synthesized at conditions of 8 GPa and 750 °C, and for the first time its crystal structure was determined using single-crystal X-ray diffraction data. PbTeO4 crystallizes with four formula units in the monoclinic space group I2/a with unit cell parameters a = 5.4142(4), b = 4.9471(4), c = 12.0437(11) Å, β = 99.603(3)°, and V = 318.07(5) Å3. UV-Vis measurements revealed UV transparency down to 200 nm. From the diffuse reflectance data experimental band gaps (Eg(direct) = 2.9 eV/Eg(indirect) = 2.8 eV) were determined and compared with calculated values. Temperature-dependent X-ray powder diffraction and complementary thermal analysis measurements revealed a stability range of PbTeO4 up to 625 °C. Additionally, theoretical calculations at DFT level of theory were carried out to obtain the electronic band structure, X-ray powder diffraction patterns, IR/Raman vibrational spectra and Mulliken partial charges. The electron localization function (ELF) was visualized to emphasize the presence of the electron lone pair E in the coordination sphere of the PbII atom.

Four UV Transparent Linear and Nonlinear Optical Materials Explored from Pure Selenite Compounds

AbstractUV nonlinear optical materials require the simultaneous achievement of a large second harmonic generation (SHG) coefficient (≥1 × KH2PO4 (KDP), dij > 0.39 pmV−1), wide bandgap (λ < 300 nm, Eg > 4.2 eV), and moderate birefringence (0.05‐0.10@1064 nm) in a single structure. Therefore, designing UV nonlinear optical materials with excellent comprehensive performance is a challenging task. Herein, four UV transparent selenite materials are successfully obtained, namely, Al2(SeO3)3(H2O)3 (1), Ga2(SeO3)3(H2O)3 (2), NaGa3(HSeO3)6(SeO3)2 (3), and Cd5Ga4(HSeO3)2(SeO3)10 (4), through rational design and screening in the pure selenite system. Al2(SeO3)3(H2O)3 (1) and Ga2(SeO3)3(H2O)3 (2) are UV nonlinear optical materials with balanced properties, exhibiting moderate SHG responses (1.2 and 1.1 × KDP), appropriate birefringence (0.084 and 0.076@1064 nm), and wide bandgaps (5.5 and 5.3 eV). Such bandgaps are the largest in the reported pure selenite nonlinear optical (NLO) materials. This work further demonstrates that pure selenite is a good candidate for UV NLO materials.

Microstructure, electronic transitions and UV transparency of K2O–B2O3–Sm2O3 glass via PbO additives

Samarium-doped borate glass is widely used in solid-state devices due to their suitable refractive index and appealing spectral characteristics. Here, we used the melt quenching technique and characterized the microstructure, optical absorption, electronic transitions and non-linear optical parameters of K2O-borate glass doped with a constant amount of Sm2O3 (1.8 mol %) and different amounts of PbO (0, 5, 10, 15 and 20 mol %), primarily using Fourier-transform Infrared (FTIR) and optical absorbance. FTIR results confirmed the strong influence of PbO on the glass internal structure. Further, inspecting the optical absorption, we found the following results. The optical absorption bands at 401, 475, 935, 1073, 1226, 1369, 1468, 1528, and 1942 nm are recognized to Sm3+ cation's electronic transitions from 6H5/2 (ground state) to 6P3/2, 4I11/2, 6F11/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2, 6H15/2 and 6H13/2 states respectively. Furthermore, for the PbO-free glass sample, an absorption band we observed at ∼220 nm in the UVC-domain. Moreover, this PbO-free glass sample is transparent in the rest of the UV-regions. A broad absorption band starts to appear with increasing the PbO concentrations in the glass system. The broadening of this band increased with further PbO additions. This band was attributed to Pb2+ cations with 6s2 species that absorb sturdily in the UV-domain. More, the glass sample doped with the highest PbO concentrations (20 mol %) can be considered a UVA transparent material, blocking UVC and UVB. Also, we found the values of Urbach energy, non-linear refractive index, third-order non-linear susceptibility, and refractive index increased for additional PbO contents, which is attributed to the increased disorder in the glass matrix. Furthermore, the results propose that the PbO-free glass sample can be used as UV-transparent material in optical applications. On the other hand, the glass sample that contains the highest PbO concentrations (20 mol %) can be used as a glass filter in some optical applications that permit UVA to pass and block UVC and UVB radiations.

UV Durable LCOS for Laser Processing

Liquid-Crystal-On-Silicon (LCOS) Spatial Light Modulator (SLM) is widely used as a programmable adaptive optical element in many laser processing applications with various wavelength light sources. We report UV durable liquid-crystal-on-silicon spatial light modulators for one-shot laser material processing. Newly developed LCOS consists of UV transparent materials and shows a lifetime 480 times longer than the conventional one in 9.7 W/cm2 illumination at 355 nm. We investigated the durability of polymerization inhibitor mixed liquid crystal in order to extend its lifetime.

The path towards wide-bandgap and UV-transparent lithium phosphate glasses doped with cobalt oxide for optical applications

We investigate ultraviolet (UV)-transmission, visible (Vis)-transmission, band stop filter properties, electron paramagnetic resonance (EPR), linear and nonlinear optical parameters of Li-P2O5- glass system with different CoO additions. These glasses were produced according to the melt quenching procedures. Transmission and EPR spectra of these glasses were recorded and studied. The band stop filter and the band pass filter are studied in Vis and UV-regions respectively. Optical absorption and EPR spectra agree with each other and they confirm the existence of Co cations in the tetrahedral coordination. We found that further Co additions result in important effects such as increasing the optical band gap (producing a wide ban gap), UV-transparency, Vis-band stop symmetry and decreasing the disorder in the present glasses. According to the obtained results, theses glasses are excellent candidates in different optical applications as an optical band stop filter, a wide band gap, and UV-transparent material.

Characterization of Optical filters using Rutherford Backscattering Spectroscopy

The composition and thickness of optical filters, especially designed for the Auger project, were measured using the RBS method. The aim of this project is to detect the extensive air showers, developed by the interaction of very energetic cosmic rays with the atmospheric air. This swarm of particles, moving at the speed of light through the atmosphere, ionizes the nitrogen atoms, which radiate UV photons in the range of 300-420 nm. This nitrogen fluorescence is subsequently detected by fluorescence detectors having optical filters placed in front of their photomultipliers with high transmittance in the region of 300-420 nm and low transmittance outside this region, in order to maximize the photon signal to background photon ratio. The required transmittance of the optical filters led to specific production techniques, such as the dielectric multi-layer thin film deposition on a substrate, using high-low index UV-transparent materials. In order to select the optimal deposition technique for the mass production of these filters, the RBS method has been used, among others, to provide information concerning the thickness of the individual layers and possible deviations from the desired stoichiometry.The optical filters presented in this work were made of 6 and 12 thin film layers of WOzjMgFi deposited on UV glass. The samples were bombarded with α-particles at EQ — 3MeV, provided by the 5.5 MV Tandem Accelerator at NCSR "Demokritos". The RBS spectra were analyzed utilizing the computer simulation code RUMP.

ChromiSense: A colourimetric lab-on-a-disc sensor for chromium speciation in water

The development of a centrifugal device for quantitative analysis of both chromium (III) and (VI) species in water is reported. ChromiSense is a colourimetric sensor system that has been applied to the measurement of chromium in spiked river water samples. For analysis, the sample is loaded into a reservoir on the disposable microfluidic disc, along with reagents. A centrifugal force is created by spinning the disc to pump liquids through microchannels, causing them to mix and react to form a coloured product. The coloured product is then presented to a low-cost optical detection system, where absorbance measurements can be recorded. The optical detection system consists of a light emitting diode (LED) and photodiode (PD) couple. Chromium (III) was measured using 2,6-pyridine dicarboxylic acid as a ligand, forming a complex that was measured at 535nm and at 335nm. While measuring at 535nm allowed for the use of a low cost LED, the sensitivity was improved 2.5 times by measuring at 335nm. However, 335nm also yielded a diminished linear range with little improvement in limit of deteciton (LOD), and required a lengthier manufacturing process due to the need for a UV-transparent material. Chromium (VI) was detected using 1,5-diphenyl carbazide (DPC). This standard analysis method was simplified for automation on-disc, and optimised to achieve a low LOD. The LOD for trivalent and hexavalent chromium using this device were 21mgL−1 and 4μgL−1, respectively. The linear range for quantitative analysis was found to be 69–1000mgL−1 for Cr(III) and 14–1000μgL−1 for Cr (VI). While this range is high for Cr(III), incorporation of an off-disc pre-concentration method would make this technology suitable for environmental sample analysis. The device is simple to use, low in cost, and could provide rapid on-site measurements, with results comparable to those obtained using a benchtop spectrophotometer.

FabSquare: Fabricating Photopolymer Objects by Mold 3D Printing and UV Curing.

The FabSquare system is a personal fabrication method that lets users fabricate objects by molding photopolymers inside a 3D printed mold. The molds are printed with UV-transparent materials that allow for UV curing--the polymerization and solidification of the fluid content. The molds can be repeatedly reused to fabricate identical objects or create new objects with identical geometry, but different components. Because the necessary equipment is easily obtainable and affordable, the FabSquare approach is suitable for ordinary users in nonspecialized labs, allowing them to rapidly fabricate a range of objects. https://extras.computer.org/extra/mcg2017030034s1.mp4https://extras.computer.org/extra/mcg2017030034s2.pdf.

UV-transparent fluoropolymer fiber coating for the inscription of chirped Bragg gratings arrays

A fluoropolymer optical fiber coating based on the thermoplastic copolymer of chlorotrifluoroethylene and vinylidene fluoride is presented. Such coatings can be used as a UV-transparent material for writing single Bragg gratings or arrays of chirped fiber Bragg gratings directly through the fiber coating with the use of excimer laser radiation at 248nm. As an optimum radiation density that does not lead to significant degradation of the fluoropolymer coating, an exposure time not exceeding 200s with a 10Hz laser pulses repetition rate at 70mJ/cm2 was identified. With such inscription parameters it was possible to inscribe arrays of fiber Bragg gratings in hydrogen-loaded birefringent optical fiber with an elliptical stress cladding through a 12µm thick coating, so that stripping of the coating is avoided and good mechanical strength is preserved. The reflection spectrum width of the chirped Bragg gratings was about 3.5nm with a reflectance coefficient of the most effective grating of up to 38%. Such Bragg grating arrays are especially interesting as reflective elements in fiber interferometers.

Photocatalytic Nanostructuring of Graphene Guided by Block Copolymer Self-Assembly.

Nanostructured graphene exhibits many intriguing properties. For example, precisely controlled graphene nanomeshes can be applied in electronic, photonic, or sensing devices. However, fabrication of nanopatterned graphene with periodic supperlattice remains a challenge. In this work, periodic graphene nanomesh was fabricated by photocatalysis of single-layer graphene suspended on top of TiO2-covered nanopillars, which were produced by combining block copolymer nanolithography with atomic layer deposition. Graphene nanoribbons were also prepared by the same method applied to a line-forming block copolymer template. This mask-free and nonchemical/nonplasma route offers an exciting platform for nanopatterning of graphene and other UV-transparent materials for device engineering.

Optically recoverable, deep ultraviolet (UV) stable and transparent sol–gel fluoro siloxane hybrid material for a UV LED encapsulant

A UV transparent and stable fluoro-siloxane hybrid material was prepared for a deep UV-LED encapsulant. The hybrimer was fabricated by hydrosilylation reaction of vinyl-fluoro oligosiloxane resin.

Enhanced optical properties of heterostructured ZnO/CeO2 nanocomposite fabricated by one-pot hydrothermal method: Fluorescence and ultraviolet absorption and visible light transparency

Many researchers investigated the properties of either discrete metal oxide CeO2 or ZnO materials. However, less attention has been paid to the various nanostructure and performances of CeO2 and ZnO nanocomposite up to now. In this paper, a facile and low cost one-pot hydrothermal synthesis method has been adopted to obtained directly precursors of CeCO3OH and Zn5(CO3)2(OH)6 with different Ce atom molar ratios to Zn, which are transformed into their corresponding metal oxide to form the ZnO/CeO2 heterostructure nanocomposites (HSNCs) by pyrolysis. The heterostructure is composed of ZnO and CeO2 monocrystals, simultaneously, CeO2 monocrystals are well dispersed on the surface of ZnO monocrystal for cosmetics. Bing dependent on the analysis results of XRD and TEM for the obtained precursors before and after pyrolysis, the formation mechanism of HSNCs was proposed. To the best of our knowledge, the paper first reported heterostructured ZnO/CeO2 nanocomposite grown in one-pot mixed aqueous solution of cerium nitrate, zinc acetate and urea without other extra surfactant. Additionally, the influence of various Ce/Zn molar ratios on the heterostructure, fluorescence emission and UV–visible absorption properties of HSNCs was investigated in detail. ZnO/CeO2 HSNCs display higher fluorescence emission with the increasing Ce/Zn molar ratio. Meanwhile, the larger Ce/Zn molar ratio of ZnO/CeO2 HSNCs, the stronger transparency in the visible light region and the weaker UV absorption. The results are due to the fact that the band gap of ZnO/CeO2 HSNCs will decrease from 3.25 to 3.08eV when Ce/Zn atom molar ratio is increased from 0 to 0.08. By the comprehensive analysis on the optical performances of HSNCs with the different Ce/Zn atom molar ratios, ZnO/CeO2-0.04 HSNCs could become UV absorber materials and transparent material in the visible region. ZnO/CeO2-0.04 HSNCs with the UV-filtering and Vis-transparent properties is appropriate for personal-care cosmetics.

Low-threshold ultraviolet solid-state laser based on a Ce^3+:LiCaAlF_6 crystal resonator

A low-threshold solid-state UV laser using a whispering gallery mode (WGM) resonator constructed from UV transparent crystalline material is demonstrated. Using a Ce3+:LiCaAlF6 resonator, we observe broad bandwidth lasing (280-330 nm) with a low threshold intensity of 7.5×10(9) W/m(2) and an effective slope efficiency of ~25%. The lasing time delay dynamics in the pulsed operation mode are also observed and analyzed. Additionally, a LiCaAlF(6) WGM resonator with Q=2×10(7) at 370 nm is realized. The combination of this high Q and the small WGM mode volume significantly lowers the pump power threshold compared to traditional cavity designs, opening the door for both tunable continuous-wave and mode-locked operation.

F2-Laser Fabrication of Fiber-Integrated Optical Elements

F2-lasers with their vacuum-ultraviolet emission wavelength of 157 nm offer the possibility to process UV-transparent materials like quartz or fused silica by direct laser ablation. This way optical quartz fiber tips can be modified in a way that special beam characteristics of the fiber-emitted light are generated, i.e. the beam shaping optic is integrated into the fiber. Two ablation methods for this modification of fiber tips have been developed, lateral processing and axial processing. Both are based on mask projection in combination with a rotation of the fiber. Precise shaping of the tip with surface roughness around 30 nm is obtained. Examples of these fiber integrated optics are lenses, cones or inverted cones. These functional fiber tips can be applied in medical technology or metrology.

Laser Induced Backside Wet Etching: Mechanisms and Fabrication of Micro-Optical Elements

A novel method for the fabrication of complex 3 dimensional structures, such as plano-convex microlens arrays in quartz, is presented. This technique is applied for precise micromachining of UV transparent materials, e.g. quartz, by using a conventional XeCl excimer laser and an organic solution which is in contact with the substrate. Strong absorption of the intense laser light results in the formation of the high pressure and temperature jumps at the quartz-liquid interface, which are the key elements in this process. A combination of laser assisted wet etching with the projection of a Diffractive Gray Tone Phase Mask is applied to fabricate diffractive and refractive micro-lens arrays in quartz. A quartz micro-lens array, which consists of 10 × 10 plano-convex microlenses is tested as a beam homogenizer for the quadrupled Nd:YAG laser.

Fabrication of microchip based on UV transparent polymer for DNA electrophoresis by F2 laser ablation

A microchip for DNA electrophoresis made of a new UV transparent polymer material (CYTOP) whose absorption edge is much shorter than 190 nm has been fabricated by F2 laser ablation. F2 laser ablation achieves high-quality microfabrication of CYTOP surface with little deterioration of the optical property and little debris deposition at etched area. The microchip in which the microchannel connected with two reservoirs was embedded was successfully fabricated by bonding the ablated sample to the virgin CYTOP sheet. The fabricated microchip was applied for DNA analysis by electrophoresis and succeeded in separating different base-pares (bp) of DNA from 50 to 766 bp with resolution of 100 bp.

A combined-nanoimprint-and-photolithography patterning technique

We propose a new lithography technique that combines the advantages of nanoimprint lithography (NIL) and photolithography. In this combined-nanoimprint-and-photolithography (CNP) technique, we introduce a hybrid mask-mold made from UV transparent material and with a light-blocking metal layer placed on top of the mold protrusions. We demonstrate that the CNP method using such a hybrid mold can achieve resist patterns without residual layer, and the resist patterns can have higher aspect ratio than the feature on the mold. In addition, the photoresist used in the CNP technique can provide higher etching durability compared with thermal plastic polymers that are commonly used in NIL.

Surface micromachining of UV transparent materials

A method which utilizes XeCl excimer laser and an absorbing liquid in contact with the material for precise structuring of UV transparent materials is presented. This one step micromachining process enables the fabrication of micro-optical elements with continuous profiles such as Fresnel micro-lenses in CaF2 and quartz with fluences well below the damage threshold of these materials. The roughness of the etched features varies from 10 nm to 3 μm depending on the laser fluence and material. The etch rates of different UV transparent materials (such as CaF2, BaF2, sapphire and quartz) at various laser fluences suggest that several different parameters influence the etching process.

Rectangular channels for lab-on-a-chip applications

We investigated the application of two technologies for the fabrication of rectangular microchannels with reasonable path lengths for UV detection in UV transparent materials. The first approach uses inductively coupled plasma (ICP)–reactive ion etching (RIE) to fabricate channels in fused silica wafers, using a 4-μm-thick nickel layer as protective mask. The effects of the process parameters on the etched channel profile and surface quality were studied directly using electron scanning microscopy, and indirectly through capillary electrophoresis experiments. In the second approach, narrow channels were easily realized in poly(dimethylsiloxane) (PDMS) using replica molding and dry-etched silicon masters. UV absorbance detection of tryptophan was possible vertically through these PDMS channels, using pre-aligned optical fibers to guide light to the channel and collect and bring the transmitted light to the detector.

Backside etching of UV-transparent materials at the interface to liquids

KrF-excimer laser etching at the interface to liquids has been studied for the fabrication of well-defined micro-structures in UV-transparent materials. The etch rates and the surface morphologies of the investigated materials including oxides (fused silica, sapphire) and fluorides (CaF 2, MgF 2) depend on the laser parameters, the used solution, and the material itself. The etch threshold fluence and the etch rates show a dependency on the liquid solvent (acetone, cyclo-hexane, tetrachloroethylene) and the concentration of the dissolved pyrene absorber molecule (0–0.4 mol/l). For quartz and sapphire two fluence regions could be distinguished. In the low fluence region, up to 1.5 J/cm 2, low etch rates up to 25 and 20 nm/pulse were found, whereas in the high fluence region, up to 3.5 J/cm 2, the rates increase to 200 and 300 nm/pulse for fused silica and sapphire, respectively. The best machining results with low surface roughness and steep walls were achieved in fused silica in the low fluence range. The examination of etched crystalline samples by RBS spectroscopy shows an amorphization of the surface after the laser interaction. Mask projection and scanning contour mask techniques were applied for the fabrication of three-dimensional micro-structures.