Adsorptive separation is very important in industry. Generally, the process uses porous solid materials such as zeolites, activated carbons, or silica gels as adsorbents. With an ever increasing need for a more efficient, energy-saving, and environmentally benign procedure for gas separation, adsorbents with tailored structures and tunable surface properties must be found. Metal–organic frameworks (MOFs), constructed by metal-containing nodes connected by organic bridges, are such a new type of porous materials. They are promising candidates as adsorbents for gas separations due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability. This critical review starts with a brief introduction to gas separation and purification based on selective adsorption, followed by a review of gas selective adsorption in rigid and flexible MOFs. Based on possible mechanisms, selective adsorptions observed in MOFs are classified, and primary relationships between adsorption properties and framework features are analyzed. As a specific example of tailor-made MOFs, mesh-adjustable molecular sieves are emphasized and the underlying working mechanism elucidated. In addition to the experimental aspect, theoretical investigations from adsorption equilibrium to diffusion dynamics via molecular simulations are also briefly reviewed. Furthermore, gas separations in MOFs, including the molecular sieving effect, kinetic separation, the quantum sieving effect for H2/D2 separation, and MOF-based membranes are also summarized (227 references).

Selective gas adsorption and separation in metal–organic frameworks

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.

Tailoring Surface Plasmons through the Morphology and Assembly of Metal Nanoparticles

Nonlinear Optical Crystals: A Complete Survey

Nd:GdVO4 crystal was grown by the Czochralski method. The absorption and fluorescence spectra of the crystal were measured at room temperature. The thermal expansion and the specific heat of the crystal were also measured. Laser outputs at 1.06 and 1.34 µm were achieved when a Nd:GdVO4 crystal sample with a high Nd doping concentration was pumped by a low-power laser diode (LD) at 808.5 nm, and visible green and red laser outputs of intracavity frequency doubling at 0.53 and 0.67 µm were also achieved when nonlinear KTiOPO4 and LiB3O5 crystal, respectively, were used. The highly Nd-doped Nd:GdVO4 crystal was pumped by a high-power LD, and a greater than 5-W laser output power at 1.06 µm was obtained. A low-Nd-doping concentration Nd:GdVO4 crystal sample was pumped by a high-power LD, yielding laser output powers at 1.06 and 0.53 µm; 0.53-µm green laser output was obtained when a KTiOPO4 crystal was used, and the output beam’s values were M2=1.76 at an output power of 14.3 W at 1.06 µm and M2=1.55 at an output power of 3.3 W at 0.53 µm. Acousto-optical Q-switched laser outputs at 1.06 and 0.53 µm were also achieved. A thermal lens made from a Nd:GdVO4 crystal was measured; it was weaker than that of a Nd:YVO4 crystal. Some important material parameters, such as temperature-induced changes in refractive index, material constant, thermal-stress resistance figure of merit, and power per unit length at the stress fracture limit, have been estimated.

Characterization of the laser crystal Nd:GdVO 4

Passive Q-switching performance was found to be greatly improved by use of a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4 compared with that achieved with Nd:YVO4 and Nd:GdVO4. At an absorbed pump power of 12 W, an average output power of 2.78 W was obtained at a pulse repetition frequency of 15.4 kHz with an optical conversion efficiency of 23.2%, and the slope efficiency was determined to be 45.5%. The resulting pulse energy, peak power, and pulse width were 181μJ, 26.6 kW, and 6.8 ns, respectively.

Improvement of passive Q-switching performance reached with a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4.

Trivalent boron as acceptor in D–π-A chromophores: synthesis, structure and fluorescence following single- and two-photon excitation

We report continuous-wave and actively Q-switched laser performance achieved with Nd:LuVO4 crystal for the F43/2→I411/2 transition (corresponding wavelength of 1065.8 nm) under high-power diode pumping. Continuous-wave output power of 12.55 W is obtained with an optical conversion efficiency of 50.2%. In actively Q-switched operation the average output power reaches 5.42 W at a pulse repetition frequency of 40 kHz with 18 W of pump power incident upon the crystal, yielding an optical conversion efficiency of 30.1%. The pulse energy and peak power reach 138 µJ and 16.2 kW, respectively, at a pulse repetition frequency of 25 kHz under a pump power of 14.2 W; the pulse duration is 8.5 ns.

Continuous-wave and pulsed laser performance of Nd:LuVO4 crystal.

Passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals has been demonstrated. Compared to Nd:YVO4 and Nd:GdVO4, the pulse energy produced with Nd:Gd0.64Y0.36VO4 under certain conditions was found to be enhanced by factors of 6.0 and 2.5, while the peak power enhanced by factors of 14.7 and 3.6, respectively. At the incident pump power of 9.6 W, 1.3 W of average output power was obtained, with the pulse energy, peak power, and pulse repetition frequency being 166 μJ, 24.5 kW, and 7.7 kHz, respectively.

Zongshu Shao

Papers

Characterization of the laser crystal Nd:GdVO 4

Improvement of passive Q-switching performance reached with a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4.

Trivalent boron as acceptor in D–π-A chromophores: synthesis, structure and fluorescence following single- and two-photon excitation

Continuous-wave and pulsed laser performance of Nd:LuVO4 crystal.

Pulse energy enhancement in passive Q-switching operation with a class of Nd:GdxY1−xVO4 crystals