光子晶体及SiO2光子晶体的制备技术

光子晶体是一种具有光子带隙的周期性电介质结构,落在光子带隙中的光将不能传播。由于其独特的调节光子传播状态的功能,成为实现光通讯和光子计算机的基础。SiO2胶体球作为胶体光子晶体的组成基元,具有广阔的应用前景。本文介绍了光子晶体的概念、特征与应用领域,以及SiO2光子晶体的制备技术。     

Artificial opals prepared by melt compression

In recent years, colloidal crystals with a refractive index varying periodically on the scale of the light wavelengths have been prepared by various methods. These photonic crystals reflect light and exhibit, at sufficiently strong contrast, even a complete band-gap in which light cannot propagate in any direction. Most studies published so far were aimed at such high-contrast photonic crystals with a complete band-gap or their precursors. Frequently, a face-centered cubic (fcc) lattice was built up from monodisperse polymer or silica spheres with diameters in the submicron range. Methods as sedimentation and drying of dispersions led to usually small and thin specimens. This report deals with films that were produced by a novel technique based on shear flow in the melts of polymer core-shell latex spheres. The process is fast and yields large area films, thin or thick, in which the latex spheres are crystallized in fcc order. The refractive index contrast of these purely polymeric films is too small for a complete band-gap photonic crystal, but the films are attractive color materials showing wavelength and angle dependent reflection colors.     

聚氨酯丙烯酸酯体系PDLC膜的制备及性能研究

本文以聚氨酯丙烯酸酯为预聚物,使用甲基丙烯酸十八烷基酯、甲基丙烯酸月桂酯、丙烯酸二甲基氨基乙酯、丙烯酸丁酯等作为稀释剂,通过相分离的方法将液晶和聚合物混合后,在紫外光的照射下,制备聚合物分散液晶膜。并在此方法下,探索了不同稀释剂单体、不同含量预聚物、液晶、光引发剂等混合的条件下所制备的PDLC材料性能。     

响应性水凝胶光子晶体的研究进展

光子晶体是由2种以上具有不同介电常数的材料按照一定的周期顺序排列成的具有有序结构的材料。响应性水凝胶光子晶体是指在一定外界条件刺激下会发生体积上的变化,进而引起光子晶体的光子带隙改变的凝胶。响应性光子晶体可分为化学响应性、物理响应性和溶剂响应性及最近应用越来越广的分子印迹响应性光子晶体。近年来响应性光子晶体凝胶在传感器、临床检测、生物方面得到广泛应用。本文就响应性光子晶体的国内外研究现状进行综述,并对其未来发展趋势进行展望。     

High-temperature stable inverse opal photonic crystals via mullite-sol-gel infiltration of direct photonic crystals

Three-dimensionally ordered macroporous materials for photonic or refractory applications have been developed by an innovative approach based on mullite sol-gel infiltration of direct photonic crystals followed by burn-out and calcination. Direct photonic crystals were obtained using polystyrene spheres templates either by vertical convective self-assembly or by drop casting. The samples were then infiltrated by spin coating with mullite sol-gels prepared with two different compositions (74 wt.% Al₂O₃, 26 wt.% SiO₂ and 80 wt.% Al₂O₃, 20 wt.% SiO₂). The inverse opal photonic crystals prepared with both sol-gels presented a highly ordered porosity and the high-alumina composition showed stability up to 1500°C. After inversion of the structure (polymeric template burn-out), the high-alumina composition showed roundness of the PS templated pores closer to an ideal sphere (Ø = 0.967) when compared to the low-alumina composition (Ø = 0.954). Although the inverse opal photonic crystals did not present a photonic bandgap, they showed structural stability at high temperatures, which enable their application as refractory materials.     

陶瓷基光子晶体的研究进展

采用以陶瓷材料为母体制备光子晶体是光子晶体制备的一个重要研究发展方向.本文介绍了陶瓷基光子晶体的几种主要的制备方法以及光子晶体在微波和红外、可见光频段中的应用.基于功能陶瓷所具有丰富的光/电功能可以制备陶瓷基光子晶体,文中介绍了可调带隙光子晶体和光子晶体中自发辐射方面的一些研究成果.陶瓷基光子晶体由于具有折射率高,功能广泛,制备手段多样等特点,因而具有广泛的应用前景,如用作电场调节的光开关和在显示领域中基于光子晶体各向异性发光特点的具有定向光发射性能的光源.     

UV-Induced Cell Death in Plants

Plants are photosynthetic organisms that depend on sunlight for energy. Plants respond to light through different photoreceptors and show photomorphogenic development. Apart from Photosynthetically Active Radiation (PAR; 400–700 nm), plants are exposed to UV light, which is comprised of UV-C (below 280 nm), UV-B (280–320 nm) and UV-A (320–390 nm). The atmospheric ozone layer protects UV-C radiation from reaching earth while the UVR8 protein acts as a receptor for UV-B radiation. Low levels of UV-B exposure initiate signaling through UVR8 and induce secondary metabolite genes involved in protection against UV while higher dosages are very detrimental to plants. It has also been reported that genes involved in MAPK cascade help the plant in providing tolerance against UV radiation. The important targets of UV radiation in plant cells are DNA, lipids and proteins and also vital processes such as photosynthesis. Recent studies showed that, in response to UV radiation, mitochondria and chloroplasts produce a reactive oxygen species (ROS). Arabidopsis metacaspase-8 (AtMC8) is induced in response to oxidative stress caused by ROS, which acts downstream of the radical induced cell death (AtRCD1) gene making plants vulnerable to cell death. The studies on salicylic and jasmonic acid signaling mutants revealed that SA and JA regulate the ROS level and antagonize ROS mediated cell death. Recently, molecular studies have revealed genes involved in response to UV exposure, with respect to programmed cell death (PCD).     

Metal oxide one dimensional photonic crystals made by RF sputtering and spin coating

We report here the analysis of the light transmission properties of one dimensional photonic crystals made by multilayers of silicon dioxide and titanium dioxide. A precise fabrication by radiofrequency sputtering of a photonic crystal allows us to accurately model the transmission spectrum of the crystal, by taking into account the wavelength dependent refractive indexes of the materials. We found that, while the dispersion of silicon dioxide is in good agreement with data reported in literature, the dispersion of titanium dioxide is more critical. Using such dispersions we could fit the transmission spectra of silicon dioxide/titanium dioxide one dimensional photonic crystals made by spin coating layer deposition starting from nanoparticle colloidal dispersions. The fit takes into account the porosity of the layers and the losses due to Rayleigh scattering.     

一维磁振子晶体带隙结构的研究

近年来,对磁振子晶体的研究已成为热点,与光子晶体等复合材料的性质类似,磁振子晶体也有带隙现象出现,频率在带隙范围内的自旋波在磁振子晶体内将被禁止传播。由此磁振子晶体有望能够被应用于广泛的仪器制造中。本文采用平面波展开法数值计算了分别由铁与钴、铁与氧化铀、钴与氧化铀材料构成的一维无限大各向同性的磁振子晶体的带结构,讨论了不同的填充率对磁振子晶体带隙结构的影响。计算结果表明,交换作用场对自旋波带宽的影响很明显。     

Photoemission from Bi-doped calcium aluminate glasses similar to sunlight

Light sources as the substitution for sunlight play an important role due to their practical applications in aircraft, medicine, and agriculture. Bi³⁺ ions show tunable emission from ultraviolet to deep red depending on local crystal field, presenting great potential in mimicking sunlight. However, these emissions are mainly limited to crystals. To stabilize Bi³⁺ ions inside photonic glasses with desirable emission and excellent physical properties remains challenging. Here, we managed to stabilize Bi³⁺ with ultrabroad and tunable emission inside glasses at air atmosphere. This emission spans the whole visible range of 350-780 nm and matches well with the sunlight spectra. For the first time, an external quantum efficiency of 34% was obtained from Bi-doped photonic glasses without optimizing glass composition. We find that the local oxidation atmosphere from super-oxide ions and proper crystal field formed by AlO₄ are responsible for this unique luminescence, which is revealed by the detailed comparison on the optical and structural properties of calcium aluminate glasses and Ca₁₂Al₁₄O₃₃ crystals with the same composition. Moreover, glasses with distortion structure further results in multiluminescent centers of Bi³⁺ so as to broaden the emission band. This work provides new insights into the luminescent behaviors of Bi ions in luminescent materials, and should contribute to designing new photonic glasses in future.     

Resonant Photonic States in Coupled Heterostructure Photonic Crystal Waveguides

In this paper, we study the photonic resonance states and transmission spectra of coupled waveguides made from heterostructure photonic crystals. We consider photonic crystal waveguides made from three photonic crystals A, B and C, where the waveguide heterostructure is denoted as B/A/C/A/B. Due to the band structure engineering, light is confined within crystal A, which thus act as waveguides. Here, photonic crystal C is taken as a nonlinear photonic crystal, which has a band gap that may be modified by applying a pump laser. We have found that the number of bound states within the waveguides depends on the width and well depth of photonic crystal A. It has also been found that when both waveguides are far away from each other, the energies of bound photons in each of the waveguides are degenerate. However, when they are brought close to each other, the degeneracy of the bound states is removed due to the coupling between them, which causes these states to split into pairs. We have also investigated the effect of the pump field on photonic crystal C. We have shown that by applying a pump field, the system may be switched between a double waveguide to a single waveguide, which effectively turns on or off the coupling between degenerate states. This reveals interesting results that can be applied to develop new types of nanophotonic devices such as nano-switches and nano-transistors.     

Ozone Generation with Narrow–Band UV Radiation

Ozone formation in oxygen at atmospheric pressure following the photodissociation of O₂ molecules in the vacuum UV range is tudied. A new VUV source based on incoherent xenon excimer radiation from a dielectric–barrier discharge provided narrow–band UV radiation at 172 nm with a half–width of 14 nm. The formation of ozone from the initial photodissociation fragments O(³P) and O(¹D) is treated theoretically and compared to measurements.     

Antiadhesion elastomer seal coatings for UV and atomic oxygen protection

Radiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low‐Earth‐orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time‐line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push‐off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 mg/cm². Coated seals were exposed to AO and UV in the NUV (near‐UV) and UV‐C wavelength ranges (300 to 400 nm and 254 nm, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.5 MJ/m² day. Exposures between 0 and 147 MJ/m² (UV‐C) and 245 MJ/m² (NUV) were accomplished. The protective coatings were durable, providing protection from UV after a simulated docking and undocking cycle. The level of protection begins to decline at coverage rates less than 0.9 mg/cm². The leakage of seals coated with Braycote + 20%Z‐cote ZnO sunscreen increased by a factor of 40 after moderate AO exposure; indicating that this coating might not be suitable due to AO intolerance. Seals coated with DC‐7–16.4%Z‐cote ZnO sunscreen were not significantly affected by combined doses of 2 × 10²¹ atoms/cm² AO with 73 MJ/m² UV‐C. Unprotected seals were significantly damaged at UV‐C exposures of 0.3 MJ/m² and DC‐7–16.4%Z‐cote coated seals were undamaged at all exposures up to the limits tested thus far which were 147 MJ/m² UV‐C and 245 MJ/m² NUV. The coatings decreased adhesion sufficiently for docking seals at temperatures equal to or greater than ?8°C thus offer a simple and inexpensive way to mitigate adhesion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41662.     

Bromate Destruction by UV Irradiation and Electric Arc Discharge

Bromate ion destruction by UV irradiation using either a low pressure mercury lamp or a medium pressure mercury lamp has been evaluated. A low pressure lamp which emits radiation predominantly at < 200 nm was more effective than the UV lamp which emits radiation at 254 nm, since bromate ion has a peak absorbance of about 195 nm. Bromate ion was shown to be reduced to bromide ion with bromine as an intermediate. Bromate ion destruction using a low pressure mercury lamp (< 200 nm) ranged from 3 to 38% for doses ranging from 23 to 228 mW-s/cm²; 7-46% destruction was achieved using a medium pressure lamp with initial bromate ion concentrations of 11-38 μg/L and doses ranging from 60 to 550 mW-s/cm². A new innovative electric arc discharge method also has been evaluated and compared with UV irradiation. The electric arc discharge method destroyed 12-45% bromate ion for doses ranging from 130 to 1300 mW-s/cm².     

Validation of the reciprocity law for coating photodegradation

Accelerating the photodegradation of commercial polymeric materials has great practical importance in the weathering community. However, questions exist as to whether high radiant flux exposure results can be extrapolated to in-service exposure levels. Based on the reciprocity law, the photoresponse of a material is dependent only on the total energy to which the specimen is exposed, and is independent of the exposure time and the intensity of the radiation taken separately. An experiment to validate the applicability of the reciprocity law for polymeric coatings has been carried out using the NIST integrating sphere-based ultraviolet (UV) weathering device. A nonpigmented, non-UV stabilized acrylicmelamine coating was exposed to six different UV radiation intensities ranging from 36 W/m² to 322 W/m², and in the spectral region between 290 nm and 400 nm. Chemical changes in the coating due to UV exposure were measured with transmission Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. Using two dose-damage models, the reciprocity law photoresponse for this polymeric system was verified for different photodegradation mechanisms, including chain scission, oxidation, and mass loss. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Mid-infrared luminesce of ZnS:Cr2+-glass composite and fiber

Cr²⁺-doped materials with mid-infrared (Mid-IR) broadband luminescence are of fundamental importance for various applications, such as solid-state lasers technology, biolabeling, optical telecommunication, and solar energy management. Especially, Cr²⁺-doped glass has been considered as one of important material candidates. The major challenge is the precipitation of crystals doped with Cr²⁺ ions in glass. So, “crystals in glass composite” is an effective method to solve this issue. Here, we describe a ZnS:Cr²⁺ in borophosphate glass composite (CZPB) which exhibits Mid-IR luminescence in the region from 1700 to 2900 nm with the full width at half maximum (FWHM) of about 690 nm. In addition, the materials can also be fabricated into fiber without obvious change in the characteristic luminescence band. The results provide new opportunities for the construction of the broadband fiber light source operating at Mid-IR waveband region.     

Enhanced Visible Light Absorption in a Photocatalytic Thin Film from a Decoupled Photonic Crystal

The optical and photocatalytic properties of a photonic crystal structure were examined to elucidate the origin of the enhanced visible light absorption from semiconductor photonic crystals. Both an enhancement in visible light absorption and an increase of the photoactivity of the semiconductor photocatalyst were found when a photonic crystal layer was decoupled from the photocatalytic film. The decoupling clearly shows that the optical enhancement arose from the dielectric mirror effect of the photonic crystal. As such, the enhancement was maximized by matching the high light absorbance region of photocatalytic semiconductors with the characteristic photonic band gap of the decoupled photonic crystal layer under various illumination conditions. For enhanced visible light photocatalytic activity, the decoupled photonic crystal layer does not have to be made from the same light-harvesting materials, but can be synthesized by a wide range of materials for ease of the fabrication process.     

Arylmethyl sulfones: A new class of photoacid generators

The X-ray and deep UV radiation response is described for resist systems consisting of poly(4-tert-butoxycarbonyloxystyrene-co-sulfur dioxide) PTBSS combined with an arylmethyl sulfone. A 2:1 4-tert-butoxycarbonyloxystyrene (TBS): sulfur dioxide (SO₂) resist has been found to function as a highly sensitive, 1.4 nm X-ray, single-component, chemically amplified resist. The same resist, however, exhibits reduced sensitivity to 0.8 nm X-rays and deep UV (248 nm) radiation. Improvement in 0.8 nm X-ray sensitivity is achieved by the addition of 12 mol% bis(3,4-dichlorobenzyl) sulfone (DCBS) to the 2:1 TBS:SO₂ resist. For this two-component resist formulation, the 0.8 nm X-ray sensitive improved from >375 to 125 mJ/cm². Similarly, the sensitivity of the 3:1 TBS:SO₂ copolymer to deep UV radiation improves to 40 mJ/cm² with addition of 10 mol% DCBS. Sulfones, such as DCBS, provide two-component resist formulations capable of <0.5 μm resolution.     

Perovskite quantum dots growth in situ in transparent medium for short wavelength shielding

High energy ultraviolet (UV) and blue light (short wavelength) radiation is proved to be harmful to human eyes, skin, and biological genomes. However, developing effective shielding materials providing protect from short wavelength is still a great challenge. Here, Eu³⁺-doped CsPbBr₃ embedded in a transparent glass medium is proved to shield the short wavelength from 200 to 475 nm with high performance, which is prepared by a facile and efficient melting-quenching technique. The uniform distribution of the CsPbBr₃ quantum dots (QDs) growth in situ from the transparent glass matrix ensures the high transmittance (>90%) at the long wavelength (520-800 nm). In addition, the excellent short wavelength shielding ability of the Eu³⁺-doped CsPbBr₃ glass ceramics (EGC) is demonstrated even suffered with accelerated weathering tests as long as 480 hours. Moreover the cell viability of A549 cells is well preserved thanks to the completely blocked blue light by the as-obtained EGC, which unambiguously demonstrates the promising application of EGC as short wavelength shielding materials.     

Near infrared emitting Cr3+ doped Zn3Ga2Ge2O10 long persistent phosphor for night vision surveillance and anti-counterfeit applications

The Cr³⁺ doped Zn₃Ga₂Ge₂O₁₀ long persistent phosphor materials were synthesized by solid state reaction method. The crystal structure of the synthesized phosphors are cubic with space group Fd3m. The band gap of the undoped host is about 4.48 eV. The materials show three photoluminescence excitation bands peaked at 260 nm, 412 nm and 580 nm. Due to the broad excitation band, the phosphors can be excited by UV light or visible light or sunlight. The phosphors shows a photoluminescence emission band peaked at 698 nm when excited by UV light. The afterglow emission shows a broad emission band with maximum at 700 nm. The detection of NIR light from the sample was observed by Night Vision Monocular for 24 h after switch off the excitation source. A mechanism is introduced to describe afterglow phenomenon and trap depth was calculated from thermoluminescence curve. As the material emit NIR persistent light, it was used as a secret light source for night vision devices. The developed material was used for tagging, tracking and locating purposes in defence application. The acrylic based paint was prepared to develop long persistent near infrared (NIR) paint, which can be coated on combat vehicle, ship, weapon, helmet, cloth, tent, rock for defence application. The NIR security ink was prepared and demonstrated to prevent counterfeit. Encryption and decryption method of confidential information was presented by using NIR security ink.