Photochemical generation of electrons and holes in germanium-containing ITQ-17 zeolite

Laser flash photolysis of germanium-containing ITQ-17 zeolite (Ge/ITQ-17, a single polymorph of beta zeolite) at 266 nm generates a transient spectrum decaying in the sub-millisecond time scale that is compatible with the formation of two transient species. The shorter lived transient (tau approximately 45 micros under nitrogen) has been assigned to trapped electrons due to the characteristic spectroscopic absorption (single band at 480 nm) and its quenching by typical electron scavengers such as N(2)O and CH(2)Cl(2). The second longer lived transient (lambda(max) = 500, 540, and 600 nm; tau approximately 390 micros) is not quenched by O(2) or electron scavengers, but it is quenched by methanol as hole scavenger and has been assigned to positive holes. Also there is a remarkable similarity of the transient spectrum of the Ge/ITQ-17 with the optical spectrum reported previously for electron-hole pairs in ZSM-5 zeolite. Under the same irradiation conditions, photoejection of electrons and photogeneration of positive holes has not been observed for conventional aluminosilicate zeolites, all-silica zeolites, or GeO(2)-impregnated zeolites. Therefore this photochemical behavior has been ascribed to the presence of framework germanium atoms opening the way for photoresponsive zeolites. The ability of Ge/ITQ-17 to generate photochemically electrons and holes has been confirmed by adsorbing naphthalene and propyl viologen sulfonate as electron donor and acceptor, respectively, and observing the generation of the corresponding radical ions.     

Synthesis,Characterization and Control of Proportion of Polymorph C in ITQ-16 and ITQ-17 Films

Continuous ITQ-16 and ITQ-17 films on silicon wafer were prepared in fluoride media using TEAOH as organic structure-directing agent. The proportion of polymorph C in the as-synthesized ITQ-16 and ITQ-17 films was determined via X-ray diffraction characterization. The proportion of polymorph C in the ITQ-16 and ITQ-17 films was controlled via optimizing the compositions of the reaction mixtures and reaction conditions, such as varying the Si/Ge molar ratio and adding n-propyl alcohol as a solvent in the reaction mixture. The Ge atoms in the reaction media strongly increased the crystallization of polymorph C in ITQ-16 and ITQ-17 films. Moreover, the stabilizing and buffering effect of n-propyl alcohol on crystal growth further enhanced the proportion of polymorph C in the ITQ-16 and ITQ-17 films. For potential catalytic applications, Al was incorporated into the framework of polymorph C, and a pure phase of polymorph C in Al-ITQ-17 film was achieved from the synthesis gel in the n-propyl alcohol phase.     

Characterization of germanium site distribution in zeolite ITQ-7 by photoluminescence

Zeolite ITQ-7 containing germanium emits luminescence upon excitation at the wavelength of the absorption maxima; control experiments with amorphous GeO2 and all-silica zeolites indicate that the emission is attributable to Ge atoms occupying framework positions; the emission decays on the nanosecond time scale and it fits to variable proportions of three exponential kinetics, this being compatible with the presence of three families of Ge atoms in the solid.     

Red to blue tunable upconversion in Tm3+-doped ZrO2 nanocrystals

The effect of dopant concentration on the blue upconversion (UPC) emission of Tm(3+) -doped ZrO(2) nanocrystals under different excitation wavelengths in the red region is reported. The UPC emissions are due to the f-f electronic transitions from excited states (1)G(4) and (1)D(2) of Tm(3+). We observed a chromatic change in the UPC with tuning the excitation wavelength. The UPC emission bands at 475, 488, and 501 nm are observed under excitation at 649 nm, but bands centered at 454 and 460 nm are observed when the excitation wavelength is tuned to 655 nm. The UPC emission could be tuned from 501 to 454 nm ( approximately 47 nm) by changing the excitation wavelength from 649 to 655 nm ( approximately 6 nm). The pump power dependence of the emission bands at 475, 488, and 501 nm were investigated on excitation intensity at 649 nm, and the emission bands at 454 and 460 nm are investigated on excitation intensity at 655 nm, which confirms that all of these UPC emission lines are a two-photon absorption process.     

Luminescence Property and Synthesis of Sulfur-doped ZnO Nanowires by Electrochemical Deposition

"Sulfur-doped zinc oxide (ZnO) nanowires were successfully synthesized by an electric field-assisted electrochemical deposition in porous anodized aluminum oxide template at room temperature. The structure, morphology, chemical composition and photoluminescence properties of the as-synthesized ZnO:S nanostructures were investigated. X-ray diffraction and the selected area electron diffraction results reveal that the as-ynthesized products are single phase with hexagonal wurtzite structure with a highly preferential orientation in the (101) direction. Transmission electron microscopy observations indicate that the nanowires are niform with an average diameter of 70 nm and length up to several tens of micrometers. X-ray photoelectron pectroscopy further reveals the presence of S in the ZnO nanowires. Room-temperature photoluminescences observed in the sulfur-doped ZnO nanowires which exhibits strong near-band-edge ultraviolet peaks at 378 and 392 nm and weak green emissions at 533 and 507 nm. A blue emission at 456 nm and violet emissions at around 406, 420, and 434 nm were also observed in the PL spectrum for the as-synthesized ZnO:S nanowires. The PL spectrum shows that S-doping had an obvious effect on the luminescence property of typical ZnO nanowires."     

8－羟基喹啉铝掺杂聚乙烯基咔唑薄膜的光致发光及电致发光

８－羟基喹啉铝掺杂聚乙烯基咔唑薄膜的光致发光及电致发光马於光,唐建国,沈家骢,刘式墉（吉林大学分子光谱与分子结构开放实验室,集成光电子学国家联合重点实验室,长春,１３００２３）关键词聚合物,光致发光,电致发光,８－羟基喹啉铝某些有机染料作为波长转换介...     

Visible emission characteristics from different defects of ZnS nanocrystals

Various sized ZnS nanocrystals were prepared by treatment under H(2)S atmosphere. Resonance Raman spectra indicate that the electron-phonon coupling increases with increasing the size of ZnS. Surface and interfacial defects are formed during the treatment processes. Blue, green and orange emissions are observed for these ZnS. The blue emission (430 nm) from ZnS without treatment is attributed to surface states. ZnS sintered at 873 K displays orange luminescence (620 nm) while ZnS treated at 1173 K shows green emission (515 nm). The green luminescence is assigned to the electron transfer from sulfur vacancies to interstitial sulfur states, and the orange emission is caused by the recombination between interstitial zinc states and zinc vacancies. The lifetimes of the orange emission are much slower than that of the green luminescence and sensitively dependent on the treatment temperature. Controlling defect formation makes ZnS a potential material for photoelectrical applications.     

Li+共掺杂对Er3+-Yb3+∶TiO2紫外、可见和红外发光同步增强研究

采用溶胶-凝胶(Sol-gel)法制备了Li+共掺杂的Er3+-Yb3+∶TiO2粉末。976 nm激光激发下在波长350~1700 nm范围内观察到了紫外、蓝色、绿色和红色上转换发光和红外下转换发光。随着Li+共掺杂浓度由0增大到20mol%,Er3+-Yb3+∶TiO2的紫外、可见和红外发光强度同步增强。低Li+共掺杂浓度引起的Li+固溶以及高Li+共掺杂浓度引起的相变过程相继破坏了Er3+的晶体场对称性,导致紫外、可见和红外发光显著增强。结果表明共掺杂Li+是一种提高Er3+掺杂材料发光性能的有效方法。     

Bismuth oxychloride nanoflakes: interplay between composition-structure and optical properties

Strongly (001) oriented BiOCl nanoflakes have been prepared at room temperature by the controlled hydrolysis of bismuth chloride in the presence of acetylacetone. The nanoflakes thermally treated in air up to 600 °C have been studied by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Composition, structure and morphology of the nanoflakes have been correlated to their electronic absorption and luminescence properties. Irrespective of the thermal treatments, the samples are characterized by transmittance higher than 98% in the near-infrared region. In the mildly annealed specimen (≤ 200 °C), the absorption bands in the ultraviolet can be effectively exploited for the selective excitation of the blue (394 nm) and green (520 nm) photoluminescence, the latter being visible only for λ(exc) > 310 nm. Conversely, at higher temperature only the blue emission is observed which, on the basis of the observed trend, can be assigned to emitting centres located in the oxide sheet of the Bi-O-Cl stacks.     

Luminescence spectroscopy of matrix-isolated z 6P state atomic manganese

The relaxation of electronically excited atomic manganese isolated in solid rare gas matrices is observed from recorded emission spectra, to be strongly site specific. z 6P state excitation of Mn atoms isolated in the red absorption site in Ar and Kr produces narrow a 4D and a 6D state emissions while blue-site excitation produces z 6P state fluorescence and broadened a 4D and a 6D emissions. MnXe exhibits only a single thermally stable site whose emission at 620 nm is similar to the broad a 6D bands produced with blue-site excitation in Ar and Kr. Thus in Ar(Kr), excitation of the red site at 393 (400) nm produces narrow line emissions at 427.5 (427.8) and 590 (585.7) nm. From their spectral positions, linewidths, and long decay times, these emission bands are assigned to the a 4D72 and a 6D92 states, respectively. Excitation of the blue site at 380 (385.5) nm produces broad emission at 413 (416) nm which, because of its nanosecond radiative lifetime, is assigned to resonance z 6P --> a 6S fluorescence. Emission bands at 438 (440) and 625 (626.8) nm, also produced with blue-site excitation, are broader than their red-site equivalents at 427.5 and 590 nm (427.8 and 585.7 nm in Kr) but from their millisecond and microsecond decay times are assigned to the a 4D and a 6D states. The line features observed in high resolution scans of the red-site emission at 427.5 and 427.8 nm in MnAr and MnKr, respectively, have been analyzed with the W(p) optical line shape function and identified as resolved phonon structure originating from very weak (S=0.4) electron-phonon coupling. The presence of considerable hot-phonon emission (even in 12 K spectra) and the existence of crystal field splittings of 35 and 45 cm(-1) on the excited a 4D72 level in Ar and Kr matrices have been identified in W(p) line shape fits. The measured matrix lifetimes for the narrow red-site a 6D state emissions (0.29 and 0.65 ms) in Ar and Kr are much shorter than the calculated (3 s) gas phase value. With the lifetime of the metastable a 6D92 state shortened by four orders of magnitude in the solid rare gases, it is clear that the probability of the "forbidden" a 6D --> a 6S atomic transition is greatly enhanced in the solid state. A novel feature identified in the present work is the large width and shifted 4D and 6D emissions produced for Mn atoms isolated in the blue sites of Ar and Kr. In contrast, these states produce narrow, unshifted (gas-phase-like) 4D and 6D state emissions from the red site.     

蓝光钙钛矿发光二极管:机遇与挑战

金属卤化钙钛矿由于具有优异的光电性能(如:高电子/空穴迁移率,高荧光量子产率,高色纯度,以及光色可调性等),成为应用于发光二极管(LED)的理想材料。近年来,钙钛矿LED的发展十分迅速,红光和绿光钙钛矿LED的外量子效率(EQE)均已超过20%。然而,蓝光(尤其是深蓝光)钙钛矿LED的EQE以及稳定性依然相对落后,这严重制约了钙钛矿LED在高性能、广色域显示领域和高显色指数白光照明领域的应用。因此,总结现阶段蓝光钙钛矿LED的发展,并剖析其机遇与挑战,对未来蓝光甚至整个钙钛矿LED领域的发展至关重要。本文将蓝光钙钛矿LED根据光色细分为天蓝光、纯蓝光、深蓝光三大部分进行总结,回顾了三种LED器件的发展历程,并详细阐述了现阶段实现他们的主要手段以及相关的基础原理,最后分析了它们各自的问题并提出了相应的解决思路。     

Novel thermally stable poly(amine hydrazide)s and poly(amine‐1,3,4‐oxadiazole)s for luminescent and electrochromic materials

We describe the preparation, characterization, and luminescence of four novel electrochromic aromatic poly(amine hydrazide)s containing main‐chain triphenylamine units with or without a para‐substituted N,N‐diphenylamino group on the pendent phenyl ring. These polymers were prepared from either 4,4′‐dicarboxy‐4″‐N,N‐diphenylaminotriphenylamine or 4,4′‐dicarboxytriphenylamine and the respective aromatic dihydrazide monomers via a direct phosphorylation polycondensation reaction. All the poly(amine hydrazide)s were amorphous and readily soluble in many common organic solvents and could be solution‐cast into transparent and flexible films with good mechanical properties. These poly(amine hydrazide)s exhibited strong ultraviolet–visible absorption bands at 346–348 nm in N‐methyl‐2‐pyrrolidone (NMP) solutions. Their photoluminescence spectra in NMP solutions or as cast films showed maximum bands around 508–544 and 448–487 nm in the green and blue region for the two series of polymers. The hole‐transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. All obtained poly(amine hydrazide)s and poly(amine‐1,3,4‐oxadiazole)s exhibited two reversible oxidation redox couples at 0.8 and 1.24 V vs. Ag/AgCl in acetonitrile solution and revealed excellent stability of electrochromic characteristics, changing color from original pale yellow to green and then to blue at electrode potentials of 0.87 and 1.24 V, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3245–3256, 2005     

Li+共掺杂对Er3+-Yb3+:TiO2紫外、可见和红外发光同步增强研究

采用溶胶-凝胶(Sol-gel)法制备了Li+共掺杂的Er3+-Yb3+:TiO2粉末.976 nm激光激发下在波长350～1700nm范围内观察到了紫外、蓝色、绿色和红色上转换发光和红外下转换发光.随着Li+共掺杂浓度由0增大到20mol%,Er3+-Yb3+:TiO2的紫外、可见和红外发光强度同步增强.低Li+共掺杂浓度引起的Li+固溶以及高Li+共掺杂浓度引起的相变过程相继破坏了Er3+的晶体场对称性,导致紫外、可见和红外发光显著增强.结果表明共掺杂Li+是一种提高Er3+掺杂材料发光性能的有效方法.     

Transparent polymeric hybrid film of ZnO nanoparticle quantum dots and PMMA with high luminescence and tunable emission color

ZnO nanoparticle quantum dots (QDs)/poly(methyl methacrylate) (PMMA) composites are synthesized by conventional radical polymerization in the presence of 3-(trimethoxysilyl)propylmethacrylate (TPM)-modified ZnO nanoparticle QDs. Although unmodified ZnO nanoparticle QDs were precipitated in tetrahydrofuran (THF) and show only weak emissions under UV irradiation, ZnO nanoparticle QDs/PMMA composite is well dispersed in THF and shows high emissions. TPM acts as the stabilizer and promotes the compatibility between the ZnO nanoparticle QDs and the PMMA matrix. After evaporation of THF from the ZnO nanoparticle QDs/PMMA composite solution, transparent polymeric hybrid films of ZnO nanoparticle QDs and PMMA are obtained. These polymeric hybrid films are characterized by photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis. The hybrid film exhibited a high quantum yield and PL emission under ultraviolet excitation. PL emission has been successfully tuned from blue to yellow.     

Synthesis and photophysical properties of polyfluorenes bearing silicon‐based functional groups

Five polyfluorenes bearing bulky trimethylsilyl (PTMS1 and PTMS2), tris(trimethylsilyl)silyl (PTTMS1), and silsesquioxane groups (PPOSS1 and PPOSS2) were synthesized through palladium‐catalyzed Suzuki coupling reactions. In the solution state, every polymer showed comparable ultraviolet–visible spectra, and they emitted blue light with high quantum efficiency. In the solid state, however, three trimethylsilyl‐functionalized polyfluorenes indicated redshifts of the fluorescence peak. In particular, PTMS1 and PTTMS1, having a hydrogen at the C‐9 position of fluorene, also showed green‐light emissions. After the annealing of the spin‐coated films, the blue‐emissive peak decreased and the green‐emissive peak became stronger in the photoluminescence spectra of three trimethylsilyl‐functionalized polyfluorenes. In contrast, PPOSS2 showed a pure blue‐light emission in the film state and even after the thermal treatment, which could be accomplished by the encapsulation of the polymer chains by the large polyhedral oligomeric silsesquioxane molecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2119–2127, 2005     

Silicon Nano-Particles with High Resistance to Harsh Ambient Conditions

Silicon nanoparticles which have an average size of 1?nm are synthesized using electrochemical methods and their stability under high temperature and humidity conditions have been investigated. These types of Silicon nanoparticles exhibit strong blue emission (centered around 420?nm) upon excitation with ultraviolet illumination. Standard heating procedures showed that, these nanoparticles in a liquid suspension (de-ionized water) are stable to heating and they retain characteristic emissions even at elevated temperatures. Thin solid films of such Silicon nanocrystals also show good stability under plasma and oxidizing environments at high temperatures.     

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Electrospun ZnO precursor nanofibers of average diameters 122±64 nm, 117±44 nm and 110±39 nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7 nm, 25.7 nm, 25.4 nm to 20.4 nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8 at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.     

Tunable photoluminescent and cathodoluminescent properties of ZnO and ZnO:Zn phosphors

ZnO and ZnO:Zn powder phosphors were prepared by the polyol-method followed by annealing in air and reducing gas, respectively. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and photoluminescence (PL) and cathodoluminescence (CL) spectra, respectively. The results indicate that all samples are in agreement with the hexagonal structure of the ZnO phase and the particle sizes are in the range of 1-2 microm. The PL and CL spectra of ZnO powders annealed at 950 degrees C in air consist of a weak ultraviolet emission band (approximately 390 nm) and a broad emission band centered at about 527 nm, exhibiting yellow emission color to the naked eyes. When the sample was reduced at the temperatures from 500 to 1050 degrees C, the yellow emission decreased gradually and disappeared completely at 800 degrees C, whereas the ultraviolet emission band became the strongest. Above this temperature, the green emission ( approximately 500 nm) appeared and increased with increasing of reducing temperatures. According to the EPR results and spectral analysis, the yellow and green emissions may arise from the transitions of photogenerated electron close to the conduction band to the deeply trapped hole in the single negatively charged interstitial oxygen ion (Oi(-)) and the single ionized oxygen vacancy (V.O) centers, respectively.     

Preparation and optical properties of high-quality oriented of Al and Er co-doped ZnO thin films

High-quality c-axis oriented Al and Er co-doped ZnO films were prepared on the quartz glasses by sol?Cgel method. In order to obtain the optimal processing parameters for the growth of the oriented film, an L₁₆ (4⁵) orthogonal experimental design was chosen. The experimental results show the rank of 5-factors as follows: Er at.%?>?the number of coating layer?>?annealing temperature?>?Al at.%?>?the concentration of the sol. The Al and Er co-doped film prepared using the optimal parameters exhibits the preferential orientation along the c-axis perpendicular to the substrate surface. In addition, the structural, morphological and optical properties of the films were studied by X-ray diffraction, scanning electron microscopy, and UV?Cvisible spectrophotometer, respectively. The photoluminescence spectra were also used to characterize the luminescence properties of the samples. It is found that when ZnO was co-doped with 7?% Al and 1.5?% Er, the blue emission centered at 465?nm disappears and the green emission centered at 547?nm increases with a blue shift, resulted from the rapid reducing of the interstitial Zn defect, and increasing of the oxygen defects and vacancies caused by Al³⁺ and Er³⁺ dopants.     

An organic white light-emitting fluorophore

The synthesis of new benzo[a]- and [b]xanthene dye frameworks is described. A unique benzo[a]xanthene, seminaphtho[a]fluorone (SNAFR-1), is studied in a variety of media. The optimization of solution parameters and excitation wavelengths allows SNAFR-1 to display red, green, and blue emission bands of approximately equal intensities and also to produce white light. Ratiometric red (anion) and green (neutral) emissions are observed upon varying solution pH. A pH-independent violet-blue emission band is due to the addition of nucleophiles to the benzylic carbon of SNAFR-1.