Upconversion properties of Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses

Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses emitting blue, green and red upconversion luminescence at 970 nm laser diode excitation were studied. It was shown that Tm3+ behaves as the sensitizer to Er3+ for the green upconversion luminescence through the energy transfer process: Tm 3+:H-3(4) + Er3+:I-4(15/2) -> Er3+:I-4(9/2) + Tm3+:H-3(6), and for the red upconversion luminescence through the energy transfer process: Tm3+:F-3(4) + Er3+:I-4(11/2) -> TM3+:H-3(6) + Er3+:4 F-9/2. Moreover, Er3+ acts as quenching center for the blue upconversion luminescence of TM3+. The sensitization of Tm3+ to Er3+ depends on the concentration of Yb3+. The intensity of blue, green and red emissions can be changed by adjusting the concentrations of the three kinds of rare earth ions. This research may provide useful information for the development of high color and spatial resolution devices and white light simulation. (C) 2006 Elsevier B.V. All rights reserved.

High quantum fluorescence yield of Er3+ at 1.5 mu m in an Yb3+, Ce3+-codoped CaF2 crystal

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 mu m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 -> I-4(13/2) transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+ 4I11/2 level. The quaternary-doped CaF2, system shows great potential to achieve high laser performance in the 1.5 mu m region. (c) 2006 Elsevier B.V. All rights reserved.

Enhanced down conversion of photons emitted by photoexcited Er xY2-xSi2O7 films grown on silicon

Photon cutting with efficiencies up to 400% is demonstrated in Erx Y2-x Si2 O7 films grown on Si and its concentration dependence is analyzed. The cutting is the result of cross-energy-transfer processes occurring within a single rare earth (Er3+) acting as both sensitizer and activator. Similarities with upconversion are revealed and possible applications in solar cells are discussed. © 2010 The American Physical Society.

Optimizing the energy offset between dye and hole-transporting material in solid-state dye-sensitized solar cells

The power-conversion efficiency of solid-state dye-sensitized solar cells can be optimized by reducing the energy offset between the highest occupied molecular orbital (HOMO) levels of dye and hole-transporting material (HTM) to minimize the loss-in-potential. Here, we report a study of three novel HTMs with HOMO levels slightly above and below the one of the commonly used HTM 2,2′,7,7′- tetrakis(N,N-di-p-methoxyphenylamino)-9,9′- spirobifluorene (spiro-OMeTAD) to systematically explore this possibility. Using transient absorption spectroscopy and employing the ruthenium based dye Z907 as sensitizer, it is shown that, despite one new HTM showing a 100% hole-transfer yield, all devices based on the new HTMs performed worse than those incorporating spiro-OMeTAD. We further demonstrate that the design of the HTM has an additional impact on the electronic density of states present at the TiO2 electrode surface and hence influences not only hole- but also electron-transfer from the sensitizer. These results provide insight into the complex influence of the HTM on charge transfer and provide guidance for the molecular design of new materials. © 2013 American Chemical Society.

Study on Er3+ emission from the erbium-doped hydrogenated amorphous silicon suboxide film

The erbium-doped hydrogenated amorphous silicon suboxide films containing amorphous silicon clusters were prepared. The samples exhibited photoluminescence peaks at around 750 nm and 1.54 mum, which could be assigned to the electron-hole recombination in amorphous silicon clusters and the intra-4f transition in Er3+, respectively. Correlations between the intensities of these two photoluminescence peaks and oxidation and dehydrogenation of the films during annealing were studied. It was found that the oxidation is triggered by dehydrogenation of the films even at low annealing temperatures, which decisively changes the intensities of the two photoluminescence peaks. On the other hand, the increase of Er content in the erbium-doped hydrogenated amorphous silicon suboxide film will enhance Er3+ emission at 1.54 mum, while quench amorphous silicon cluster emission at 750 nm, such a competitive relationship, was also observed in the erbium-doped silicon nanocrystals embedded in SiO2 matrix. Moreover, we found that Er3+ emission is not sensitive to whether silicon clusters are crystalline or amorphous. The amorphous silicon clusters can be as sensitizer on Er3+ emission as that of silicon nanocrystals. (C) 2003 American Institute of Physics.

环糊精衍生物的设计、合成及其对环辛烯光异构化研究

环糊精(Cyclodextrins, CDs)经化学修饰后可以得到各种类型的衍生物，不仅可以扩展其原有的键合能力，而且还可以改变其选择性，是当代超分子化学的一个研究热点。环糊精第二面的仲羟基比第一面的伯羟基有着更好的催化性能，第二面的选择性修饰将产生更多有价值的衍生物，可用于催化、酶模拟、手性识别等方面。 取代苯甲酰基修饰环糊精对顺式环辛烯(cis-cyclooctene)光异构化反应有非常重要的影响作用，苯环上取代基的性质和取代位置与产物的%ee值和对映体构型之间存在某种内在联系。有目的地选择适宜取代基，设计、合成新型环糊精光增感剂, 有可能按预定目的得到更高%ee值的反式环辛烯；同时，取代苯甲酰基修饰环糊精对cis-cyclooctene光异构化的增感机理有待于进一步阐明。 本论文工作对环糊精的化学修饰以及超分子体系对cis-cyclooctene不对称光异构化反应方面的进展进行了调研。合成了一系列单-6-位取代苯甲酰基修饰环糊精，用于cis-cyclooctene光异构化增感反应，并用圆二色光谱滴定法研究这些环糊精衍生物与cis-cyclooctene的相互作用，以探索光增感反应机理。在此基础上，探讨了环糊精第二面的选择性修饰方法。内容主要包括： 1. 简要介绍了超分子化学的概况，并对环糊精的选择性修饰方法和超分子体系对cis-cyclooctene不对称光异构化反应的主要成果和最新进展进行了评述。 2. 合成了12种单-6-O-(取代苯甲酰基)-β-环糊精，其中10种为新化合物。采用紫外光谱、红外光谱、核磁共振波谱以及质谱等手段对化合物的结构进行了表征。 3. 探索了直接选择性修饰环糊精第二面的便捷新方法。用取代苯甲酰咪唑酯为酰化试剂，0.2M碳酸盐缓冲溶液(pH=9.9)作催化剂，能够有效地活化2-位仲羟基，对环糊精第二面进行选择性修饰，此方法既简便又经济；同时，发现取代苯甲酰基能够在β-CD第二面的2-位、3-位羟基间相互迁移。 4. 用单-6-O-(取代苯甲酰基)-β-环糊精作光增感剂，对cis-cyclooctene光异构化反应进行研究。实验结果证明：取代苯甲酰基上的取代基性质、位置、长度对反应的对映选择性有很大影响；此外，反应体系溶剂极性对产物的%ee值和对映体构型也有重大影响。用单-6-O-(3-甲氧苯甲酰基)-β-CD作增感剂，cis-cyclooctene光异构化反应产物(R)-trans-cyclooctene的对映选择性为45.8%ee，是到目前为止取得的最好对映选择性。 5. 采用圆二色光谱滴定法研究环糊精衍生物与cis-cyclooctene的相互作用，计算包结物的平衡常数，研究包结物的相对稳定性，为探索光增感反应机理提供基础。我们猜测：电子效应对cis-cyclooctene光异构化反应的影响，可能比取代基位置对反应的影响更大，借助电子效应有希望获得更高的%ee值。 Cyclodextrins can be subjected to diverse modifications to give a wide variety of cyclodextrin derivatives, which could not only extend their original molecular binding ability, but also alter their molecular selectivity. Therefore, cyclodextrin chemistry is currently a significant topic in supramolecular chemistry. The more open secondary hydroxyl side of CDs is stated to be catalytically very important, modifications of this face are believed to produce valuable derivatives for catalysis, enzyme mimic, chiral discrimination, etc. Mono-6-O-(substituted benzoyl)-β-CDs as novel supramolecular photosensitizing hosts have recently excited considerable attention in photochirogenesis. The supramolecular photosenstization of cis-cyclooctene mediated by them gave chiral trans-cyclooctene, enantiomeric excess of which was critically affected by the substituent introduced to the sensitizer moiety. In order to enhance the photoenantiodifferentiating ability, and elucidate the origin mechanisms of substituent-dependent enantioselectivity, in this work a series of mono-6-O-(substituted benzoyl)-β-CDs have been synthesized, and applied for enantiodifferentiating photoisomerization of cis-cyclooctene. The major contents are as follows: 1. The general aspects of supramolecular chemistry were descibed briefly. The new progress and important achievements on methods of selective modification of cyclodextrin and supramolecular enantiodifferentiating photoisomerization of cis-cyclooctene were reviewed. 2. Twelve mono-6-O-(substituted benzoyl)-β-CDs including ten novel compounds have been synthesized. Their structures have been characterized by using UV-vis, IR, NMR and MS methods. 3. A new convenient strategy for direct acylation of β-cyclodextrin on the secondary hydroxyl face was achieved by using the combination of N-benzoylimidazole and carbonate buffer in DMF, and the acyl migration between the C-2 and C-3 hydroxyl groups of β-cyclodextrin was found. 4. Experiments using mono-6-O-(substituted benzoyl)-β-CDs as chiral sensitizing hosts for mediating the enantiodifferentiating photoisomerization of cis-cyclooctene, were carried out. The results indicate that enantiomeric excess was critically affected, or even switched in sign, by the substituent introduced to the sensitizer moiety, and polarity of solvent. Using mono-6-O-(3-methoxybenzoyl)-β-CD as chiral sensitizing host, (R)-trans-cyclooctene was obtained in up to 45.8% enantiomeric excess, which is the highest value ever reported for supramolecular photochirogenesis with analogous hosts. 5. The conformational variation of these modified CDs and their complexation behaviors with cis-cyclooctene were examined by circular dichroism spectroscopy in water-methanol mixed solvents, which reveal that the orientation of chromophore was highly sensitive to the type, position and length of the introduced substituents. In the end, the complex stability constants(Ks) were calculated, and the mechanisms of reaction were discussed. Maybe, electronic effects are more important than positions of substituents for mediating the enantiodifferentiating photoisomerization of cis-cyclooctene.

Efficient red organic light-emitting diode sensitized by phosphorescent Ir compound

The efficiencies of red organic light-emitting diode (OLED) using tris-(8-hydroxy-quinoline)aluminum (Alq(3)) as host and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant were greatly increased by adding a small amount (0.3 wt%) of Ir compound, iridium(III) bis(3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-onato-N-',C-4) (acetyl acetonate) (Ir(C6)(2)(acac)), as a sensitizer

Highly efficient white organic light-emitting devices based on a multiple-emissive-layer structure

Characteristics of white organic light-emitting devices based on phosphor sensitized fluorescence are improved by using a multiple-emissive-layer structure, in which a phosphorescent blue emissive layer is sandwiched between red and green&yellow ones. In this device, bis[(4,6-difluorophenyl)-pyridinato-N,C-2] (picolinato), bis(2,4-diphenyl-quinoline) iridium (III) acetylanetonate, fac bis (2-phenylpyridine) iridium, and 5,6,11,12-tetraphenylnaphthacene are used as blue, red, green, and yellow emitters, respectively.

Enhance the optical absorptivity of nanocrystalline TiO2 film with high molar extinction coefficient ruthenium sensitizers for high performance dye-sensitized solar cells

We report two new heteroleptic polypyridyl ruthenium complexes, coded C101 and C102, with high molar extinction coefficients by extending the pi-conjugation of spectator ligands, with a motivation to enhance the optical absorptivity of mesoporous titania film and charge collection yield in a dye-sensitized solar cell. On the basis of this C101 sensitizer, several DSC benchmarks measured under the air mass 1.5 global sunlight have been reached.

Tetrahydrothiophenium-based ionic liquids for high efficiency dye-sensitized solar cells

Binary melts of S-ethyltetrahydrothiophenium iodide and dicyanoamide (or tricyanomethide) have been employed for dye-sensitized solar cells with high power conversion efficiencies up to 6.9% under the illumination of AM 1.5G full sunlight. We have further shown that the transport of triiodide in ionic liquids with high iodide concentration is viscosity-dependent in terms of a physical diffusion coupled bond exchange mechanism apart from the simple physical diffusion.

New Efficiency Records for Stable Dye-Sensitized Solar Cells with Low-Volatility and Ionic Liquid Electrolytes

We report a high molar extinction coefficient heteroleptic polypyridyl ruthenium sensitizer, featuring an electron-rich 3,4-ethylenedioxythiophene unit in its ancillary ligand. A nanocrystalline titania film stained with this sensitizer shows an improved optical absorption, which is highly desirable for practical dye-sensitized solar cells with a thin photoactive layer, facilitating the efficient charge collection.

Dye-sensitized solar cells with solvent-free ionic liquid electrolytes

We systematically studied the temperature-dependent physicochemical properties, such as density, conductivity, and fluidity, of 1,3-dialkylimidazolium iodides. In combination with the amphiphilic Z907Na sensitizer, we have found that it is important to use low-viscosity iodide melts with small cations to achieve high-efficiency dye-sensitized solar cells. By employing high-fluidity eutectic-based melts the device efficiencies considerably increased compared to those for cells with the corresponding state of the art ionic liquid electrolytes.

Near-infrared luminescent mesoporous MCM-41 materials covalently bonded with ternary thulium complexes

Two beta-diketones 4,4,4-trifluoro-1-2-thenoyl-1,3-butanedione (Htta) and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (Htfnb), which contain trifluoroalkyl chain, were selected as the main sensitizer for synthesizing Tm(L)(3)phen (L = tta, tfnb) complexes. The two near-infrared (NIR) luminescent thulium complexes have been covalently bonded to the ordered mesoporous material MCM-41 via a functionalized 1,10-phenanthroline (phen) group 5-(N,N-bis-3-(triethoxysilyl)propyl)ureyl-1,10-phenanthroline (phen-Si) [The resultant mesoporous materials are denoted as Tm(L)(3)phen-MCM-41 (L = tta, tfnb)]. The Tm(L)(3)phen-MCM-41 (L = tta, tfnb) mesoporous materials were characterized by small-angle Xray diffraction (XRD) and N-2 adsorption/desorption, and they show characteristic mesoporous structure of MCM-41.

Near-infrared luminescent xerogel materials covalently bonded with ternary lanthanide [Er(III), Nd(III), Yb(III), Sm(III)] complexes

A beta-diketone ligand 4,4,5,5,5-pentafluoro-1-(2-naphthyl)-1,3-butanedione (Hpfnp), which contains a pentafluoroalkyl chain, was synthesized as the main sensitizer for synthesizing new near-infrared (NIR) luminescent Ln(pfnp)(3)phen (phen = 1,10-phenanthroline) (Ln = Er, Nd, Yb, Sm) complexes. At the same time, a series of lanthanide complexes covalently bonded to xerogels by the ligand 5-(N,N-bis-3-(triethoxysilyl)propyl)ureyl-1,10-phenanthroline (phen-Si) were synthesized in situ via a sol-gel process. [The obtained materials are denoted as xerogel-bonded Ln complexes (Ln = Er, Nd, Yb, Sm).] The single crystal structures of the Ln(pfnp) 3phen complexes were determined.

Improved color purity and efficiency by a coguest emitter system in doped red light-emitting devices

We demonstrate red organic light-emitting diodes (OLEDs) with improved color purity and electroluminescence (EL) efficiency by codoping a green fluorescent sensitizer 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1, 1, 7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-ij)quinolizin-11-one (C545T) as the second dopant and a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the lumophore into tris(8-hydroquinoline) aluminum (Alq(3)) host. It was found that the C545 T dopant did not by itself emit but assisted the carrier trapping from the host Alq(3) to the red emitting dopant. The red OLEDs realized by this approach not only kept the purity of the emission color, but also significantly improved the EL efficiency. The current efficiency and power efficiency, respectively, reached 12 cd/A at a current density of 0.3 mA/cm(2) and 10lm/W at a current density of 0.02 mA/cm(2), which are enhanced by 1.4 and 2.6 times compared with devices where the emissive layer is composed of the DCJTB doped Alq(3), and a stable red emission (chromaticity coordinates: x = 0.64, y = 0.36) was obtained in a wide range of voltage. Our results indicate that the coguest system is a promising method for obtaining high-efficiency red OLEDs.