Dominant ultraviolet-blue photoluminescence of ZnO embedded into synthetic opal

The temperature-dependent photoluminescence (PL) characteristics of zinc oxide (ZnO) embedded into the voids of synthetic opal were studied. ZnO was infiltrated into opal from aqueous solution with zinc nitrate precursor followed by thermal annealing. The PL spectra of the ZnO powder exhibit very high and broad emission peaks in the green region due to crystal defects, such as oxygen vacancies and zinc ion interstitials. In contrast to the PL spectra of ZnO powder, nanocrystals of ZnO embedded into the voids of FCC packed opal matrix exhibit dominant ultraviolet (UV)-blue and rapidly decreasing green PL emissions with decreasing temperature. The temperature-dependent PL characteristics show that the green band suppression in the ZnO nanocrystals is due to the influence of photonic crystal. The infiltration of nanoparticles into synthetic opal may be used for the fabrication of polycrystalline ZnO with dominant UV-blue PL. These results indicate that the luminescent materials embedded into photonic crystal may be promising for the fabrication of the RGB pixels in full-color displays.     

Photoluminescence properties of bare and ZnO infilled artificial opal

Photoluminescence of bare and ZnO infilled artificial opals was investigated. A presence of a photonic band gap results in distortion of the photoluminescence spectra of both the bare and ZnO infilled opal nanocomposite. Filling of the opal with ZnO resulted in a shift of the Bragg diffraction peak from 430 to 460 nm. The emission from ZnO infilled opal contains no UV photoluminescence from ZnO nanocrystals, while the ZnO nanocrystals deposited on substrate by the same method exhibit strong excitonic UV emission. Although a high temperature treatment in ambient air results in an increase in the photoluminescence intensity of the ZnO nanocrystals, the quenched behavior of the excitonic emission from ZnO nanocrystals embedded in the opal matrix remains. A domination of the artificial opal matrix intrinsic emission in the photoluminescence spectra from the untreated as well as heat treated ZnO filled opal nanocomposites is observed.     

Equations for filling factor estimation in opal matrix. Addendum to “Deep level emission of ZnO nanoparticles deposited inside UV opal”, [Opt. Commun. 259 (1) (2006) 378-384]

We consider two equations for the filling factor estimation of infiltrated zinc oxide (ZnO) in silica (SiO₂) opal and gallium nitride (GaN) in ZnO opal. The first equation is based on the effective medium approximation, while the second one—on Maxwell-Garnett approximation. The comparison between two filling factors shows that both equations can be equally used for the estimation of the quantity of infiltrated nanoparticles inside opal photonic crystal.     

ZnO-treated TiO2 inverse opal electrodes for dye-sensitized solar cells

We report that the photovoltaic properties of inverse opal TiO₂ (io-TiO₂) electrodes in dye-sensitized solar cells can be enhanced by ZnO treatment of the inverse opal structures. ZnO was coated on the surface of io-TiO₂ via the sol–gel reaction of ZnO precursors. Energy dispersive X-ray spectroscopy (EDX) measurements showed that the amount of ZnO on the io-TiO₂ surface was measured to be 0.12–0.50 wt% of zinc, depending on the number of coatings. Compared to bare inverse opal electrodes, the energy conversion efficiency of cells increased for the 0.35 wt% ZnO-coated electrodes, and then decreased for the 0.50 wt% ZnO-coated electrodes. The maximum efficiency of 5.3% was achieved, corresponding to a 23% increase in efficiency compared with bare io-TiO₂ electrodes. The enhanced efficiency was mainly attributed to the improvement of the open-circuit voltage (V_OC). EIS and dark current measurements confirmed that this enhancement in V_OC was due to the movement of the conduction band edge in a negative direction after ZnO treatment, rather than the formation of a barrier layer for electron recombination.     

采用溶胶凝胶协同自组装与光刻相结合的方法在反蛋白石结构薄膜中引入二维缺陷

采用溶胶凝胶协同自组装与光刻相结合的方法,在光子晶体反蛋白石结构中引入缺陷,通过溶胶凝胶协同自组装方法在硅片上垂直沉积胶体晶体复合薄膜,把BP212正性光刻胶均匀旋涂在复合薄膜上,通过曝光、显影等光刻工艺,把掩膜版图案复制在复合薄膜上,用此样品再次垂直沉积一层复合薄膜,使图案被复合薄膜覆盖.最后去除胶体微球与光刻胶图案,从而在反蛋白石结构中引入缺陷,用扫描电子显微镜对样品进行表征.分析了光刻胶图案对胶体微球排列的影响.     

Deep level emission of ZnO nanoparticles deposited inside UV opal

The temperature-dependent photoluminescence spectra of zinc oxide (ZnO) nanocrystals deposited inside the ultraviolet (UV) opal were studied. ZnO was grown in the voids between FCC packed SiO₂ spheres using spray pyrolysis under ultrasonic vibration in the solution containing a zinc nitrate precursor. The ZnO nanoparticles inside opal matrix with UV photonic band-gap exhibit suppression of the excitonic emission and enhancement of the deep level emission. Suppression of the excitonic lines is due to the inhibition of spontaneous emission, while enhancement and broadening of the DL emission in the green spectral region is due to Purcell effect. The infiltration of ZnO nanoparticles inside the photonic crystal may be a useful technique to increase its emission efficiency in the selected spectral region.     

ZnO filled opal arrays: Photo and cathodoluminescence studies

The photo and cathodoluminescence of zinc oxide (ZnO) filled opal arrays, as well as ZnO nanocrystals prepared by a chemical deposition method were investigated. The photoluminescence (PL) from the arrays was studied using angular resolution. The PL spectra of the filled opal exhibited a dip corresponding to the array’s photonic band gap. ZnO nanocrystals embedded in the opal matrix demonstrated quenched excitonic emission while the opal matrix showed enhanced emission. This effect is explained by an energy transfer from ZnO nanocrystals to the opal matrix.     

Large-scale ZnO inverse opal films fabricated by a sol–gel technique

We demonstrate that high-quality large-scale ZnO inverse opals can be fabricated by a simple sol–gel technique, comprising infiltration of polystyrene colloidal crystal films with zinc nitrate solution, drying and annealing at 300 C. This simple method yields continuous films, which consist of inverse opal domains (up to several hundreds of μm² in size), separated by small cracks filled with zinc oxide. Microradian X-ray diffraction was employed to verify the crystalline quality of ZnO inverse opals on the macroscale, revealing that the samples have a predominant face-centered cubic structure, and that the majority of domains have the same crystallographic orientation. The samples exhibit bright iridescence and possess photonic stop-bands in the visible to near-infrared spectrum.     

Nanostructural effects on optical properties of tungsten inverse opal

Tungsten (W) photonic crystals are very attractive because of their potential applications in the conventional lighting field. In this work we show that W nanostructures have dominative effects on optical properties of W inverse opal. The nanoparticle structure of W phase can cause intensive optical absorption and breakdown of the photonic band gap; on the contrary, W inverse opal made from bulk and compact W phase would have weak absorption and possess a good photonic band gap. The results will throw a new light on the study and application of W photonic crystals and development of other photonic crystal and black-body materials. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Infiltration of colloidal crystal with nanoparticles using capillary forces: a simple technique for the fabrication of films with an ordered porous structure

A dipping method has been developed for the infiltration of nanoparticles into an opal template to fabricate high quality inverse opal. Titania and silica inverse opal films, with a uniform color over centimeter dimensions were derived. As there is no need for special substrates or equipment, a widespread application of this method is anticipated. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 30 October 2001     

Fabrication of anatase titania inverse opal films using polystyrene templates

High-performance titania inverse opal films have been derived from a sol–gel procedure using polystyrene colloidal crystals as templates. By carefully controlling the synthetic procedures, the titania inverse opal films display a uniform color over centimeter dimensions. Scanning electron microscopy is employed to characterize the qualities of the titania inverse opal films. Electron diffraction pattern shows a polycrystalline anatase structure of TiO₂.     

Photonic band gap properties of GaP opals with a new topology

In this paper, we propose that the “anomalous” optical response exhibited by GaP and InP infiltrated opals is due to the peculiar morphology shown by these materials when grown within the pores. In order to account for their optical response, we propose a new structural model consisting of a network of high dielectric spheres located in the pores of the bare opal, interconnected by cylinders of the same material. A fair agreement between the theoretical predictions using this model and the experimental measurements has been found. We also show that the inverse structure presents very interesting optical properties.     

Preparation and upconversion emission properties of TiO2 :Yb, Er inverse opals

Inverse opal photonic crystals of Y b³⁺, Er³⁺ co-doped TiO₂ (TiO₂:Yb, Er) were prepared by a self-assembly technique in combination with a sol-gel method. Upconversion (UC) luminescence properties of the inverse opals were investigated. The results show that photonic bandgap has significant influence on the upconversion emission of the TiO₂:Yb, Er inverse opal photonic crystals. Significant suppression of the upconversion emission was detected if the photonic bandgap overlapped with the Er³⁺ ions emission band.     

光全息制作的变形面心立方结构光子晶体的带隙

四束激光从空气直接入射到平面结构的感光树脂所制备的面心立方结构实际上是一种不但晶格沿[111]方向拉伸,而且其格点也在[111]方向被拉长的变形面心立方结构。在对这种变形面心立方结构的光子晶体的晶格形状及能带分布的研究中,通过利用麻省理工学院的光子晶体能带计算程序计算了各种参量对此变形面心立方结构的蛋白石和反蛋白石的能带分布的影响,发现在一定条件下该结构的蛋白石会出现完全光子带隙。用激光全息聚合法在正胶的环氧树脂中可制作反蛋白石模板,若用此模板制作硅蛋白石,当晶格沿[111]方向拉伸2.1倍和硅的占空比为13.7%时出现最大的带隙宽度。此最大带隙宽度的结构的制作光路是三角锥形光路,对称地环绕中央光束的三束外围激光束之间夹角为54.0°,三束外围激光束与中央激光束夹角为31.6°。     

采用溶胶凝胶协同自组装方法制备SiO2反蛋白石结构薄膜及其光学性质研究

研究了溶胶凝胶协同自组装制备大面积高质量SiO₂反蛋白石结构薄膜的方法. 向单分散的聚苯乙烯(PS)胶体溶液中添加SiO₂前驱物溶液,用垂直自组装法一步得到微球空隙中均匀填充有凝胶的 复合PS胶体晶体薄膜,在空气中烧结去除PS后得到SiO₂反蛋白石结构薄膜.通过对添加前驱物溶液比例、 自组装温度以及烧结温度等参数的研究,用不同粒径的PS微球制备了不同孔径的高质量SiO₂反蛋白石结构薄膜. 用扫描电子显微镜和X射线能量色散谱仪对制备得到的薄膜样品进行显微形貌和成分表征,并测试了其透射光谱. 结果表明:溶胶凝胶协同自组装法制备的SiO₂反蛋白石结构薄膜大面积高度有序,孔径可以控制且选择范围宽; 薄膜的透射光谱带隙明显,带隙中心波长与理论计算结果相符.     

圆柱形蛋白石和反蛋白石结构光子晶体的制备及其光学性质

研究了在圆柱曲面基底上自组装空心和实心的圆柱形蛋白石和反蛋白石结构光子晶体的方法. 用垂直沉积法在不同曲率半径的毛细管内自组装了空心圆柱形聚苯乙烯(PS)蛋白石结构光子晶体薄膜和二氧化硅 (SiO₂) 反蛋白石结构薄膜; 用类重力沉积法制得实心圆柱形蛋白石和反蛋白石结构光子晶体, 并讨论了这一生长方式中的状态变化过程及影响因素. 用扫描电子显微镜对样品内部结构进行了表征, 用光谱仪测试了光子晶体薄膜的反射光谱, 结果表明: 基底曲率半径和微球粒径的大小是影响空心蛋白石和反蛋白石薄膜质量的主要因素; 微球大小是影响实心结构有序性的主要因素. 关键词： 反蛋白石 空心圆柱 溶胶凝胶协同自组装     

Controlling the photoluminescence spectroscopy of quinacrine dihydrochloride by SiO_2 inverse opal photonic crystal

Manipulation of the photoluminescence spectra of light-emitting materials doped in three-dimensional （3D） inverse opal photonic crystals is investigated. Quinacrine dihydrochloride molecules doped highly ordered SiO2 inverse opal is successfully synthesized by co-assembly combined with double-substrate vertical infiltrate method. The quinacrine dihydrochloride-doped and-undoped SiO2 inverse opals each exhibit an apparent photonic band gap （PBG） in the visible light region. Significant suppression of the emission is observed when the PBG is overlapped with the quinacrine dihydrochloride emission bands. The mechanism of suppression effect of PBG in inverse opal on the fluorescence intensity of quinacrine dihydrochloride molecules is studied.     

Stimulated emission at the second order stop-zone edge of the two-dimensional opal–zinc oxide photonic crystal

The fabrication of the 2D periodic structures in ZnO thin films by magnetron sputtering on the opal matrices was developed. The microstructures were characterized by AFM and SEM. The spontaneous and stimulated emissions of the ZnO layers on opal were studied at N₂ laser excitation (λ = 337 nm). The stimulated emission near 397 nm was observed at room temperature from ZnO–opal structure. The threshold of the electron–hole plasma recombination laser process was 300 kW/cm² for this structure. This threshold is two orders of magnitude smaller of that one for the flat ZnO–SiO₂ films owing to DFB resonator effect in 2D structure.     

Photoluminescence in Gd2O3: Er3+, Yb3+ upconversion inverse opal

Photoluminescence properties of Gd₂O₃: Er³⁺, Yb³⁺ upconversion inverse opal photonic crystals were investigated. The photoluminescence spectra of the inverse opal show strong dependence on upconversion emission intensity and the corresponding photonic band-gaps of the inverse opal. Significant suppression of the green or red upconversion emission was observed if the photonic band-gap overlaps with the Er³⁺ ions emission band. The color purity of the red or green emission was improved in the inverse opal by the suppression of green or red UC emission. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also new optical devices in upconversion lighting and display.     

Effect of Sn concentration on structural and optical properties of zinc oxide nanobelts

We investigated structural and optical properties of Sn-doped ZnO nanobelts with different Sn concentrations. X-ray diffraction and Raman spectra showed that the Sn-doped ZnO nanobelts have wurtzite structure at low Sn concentration (<2.1 at%) and over 2.1 at% a part of them starts to have the inverse spinel Zn₂SnO₄ structure phase. In addition, for Sn-doped ZnO nanobelts, the photoluminescence spectra indicate that ultraviolet emission peak appears first a blue shift with the increase of Sn concentration due to Burstein-Moss effect and then exhibits a red shift due to band gap renormalization effect.