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

In the last two decades, plasmon resonance in gold nanoparticles (Au NPs) has been the subject of intense research efforts. Plasmon physics is intriguing and its precise modelling proved to be challenging. In fact, plasmons are highly responsive to a multitude of factors, either intrinsic to the Au NPs or from the environment, and recently the need emerged for the correction of standard electromagnetic approaches with quantum effects. Applications related to plasmon absorption and scattering in Au NPs are impressively numerous, ranging from sensing to photothermal effects to cell imaging. Also, plasmon-enhanced phenomena are highly interesting for multiple purposes, including, for instance, Raman spectroscopy of nearby analytes, catalysis, or sunlight energy conversion. In addition, plasmon excitation is involved in a series of advanced physical processes such as non-linear optics, optical trapping, magneto-plasmonics, and optical activity. Here, we provide the general overview of the field and the background for appropriate modelling of the physical phenomena. Then, we report on the current state of the art and most recent applications of plasmon resonance in Au NPs.

Surface plasmon resonance in gold nanoparticles: a review.

Photothermal materials with broad solar absorption and high conversion efficiency have recently attracted significant interest. They are becoming a fast-growing research focus in the area of solar-driven vaporization for clean water production. The parallel development of thermal management strategies through both material and system designs has further improved the overall efficiency of solar vaporization. Collectively, this green solar-driven water vaporization technology has regained attention as a sustainable solution for water scarcity. In this review, we will report the recent progress in solar absorber material design based on various photothermal conversion mechanisms, evaluate the prerequisites in terms of optical, thermal and wetting properties for efficient solar-driven water vaporization, classify the systems based on different photothermal evaporation configurations and discuss other correlated applications in the areas of desalination, water purification and energy generation. This article aims to provide a comprehensive review on the current development in efficient photothermal evaporation, and suggest directions to further enhance its overall efficiency through the judicious choice of materials and system designs, while synchronously capitalizing waste energy to realize concurrent clean water and energy production.

Solar absorber material and system designs for photothermal water vaporization towards clean water and energy production

This critical review will present the role of nanoparticles (NPs) in the directions that are vital to the new field of nanomedicine, including imaging and drug delivery. We reflect on the physical properties that make NPs advantageous for in vivo efficacy, and review recent advances in major NP based biomedical applications. Critical questions of transport, uptake, and clearance will be discussed and illustrated through the success and opportunities of NP imaging and therapy on a photodynamic therapy (PDT) based NP system that has been developed in our lab over the past decade (540 references).

The unique role of nanoparticles in nanomedicine: imaging, drug delivery and therapy

Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

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25th Anniversary Article: Semiconductor Nanowires – Synthesis, Characterization, and Applications

We report the light-to-heat energy transfer efficiencies of gold nanoparticles with variable sizes by assessing the temperature profiles of laser-activated particle suspensions in water. Gold nanoparticles with sizes ranging from 5 to 50 nm were synthesized by chemical reduction methods using sodium borohydride, sodium citrate, or hydroquinone as reducing agents. As-synthesized gold nanoparticle solution (1 mL) was loaded into a quartz cuvette and exposed to a CW green laser (532 nm). Heat input into the system by energy transfer from nanoparticles equals heat dissipation at thermal equilibrium. The transducing efficiency was then determined by plotting temperature increase as a function of laser power extinction. The efficiency increases from 0.650 ± 0.012 to 0.803 ± 0.008 as the particle size decreases from 50.09 ± 2.34 to 4.98 ± 0.59 nm, respectively. The results indicate that the photothermal properties of gold nanoparticles are size-tunable, and the variation of efficiency can be correlated to the ab...

Size-Dependent Photothermal Conversion Efficiencies of Plasmonically Heated Gold Nanoparticles

Single crystal In(OH)3 nanocubes were synthesized by a designed novel hydrothermal treatment, and the size can be simply moderated by varying the hydrothermal temperature By calcining the In(OH)3 nanocubes in air at 400 °C, single crystal In2O3 nanocubes were also prepared with the size slightly shrinking Room temperature photoluminescence showed a broad photoluminescence emission spectrum in the blue-green region with its maximum intensity centered at 450 nm, which was mainly attributed to the effect of the oxygen deficiencies

Size-Controllable Growth of Single Crystal In(OH)3 and In2O3 Nanocubes

Morphology control of stolzite microcrystals with high hierarchy in solution.

Unusual ZnO superstructures with nanosheets standing on the backbone of spindle-like rods were synthesized for the first time from a flakelike Zn5(OH)8Cl2·H2O precursor under mild solution conditions without using high temperature or any organic molecular templates. The formation of the ring-like nanosheets standing on the spindle is related to the special morphology of the precursor and its solubility, as well as the refluxing reaction conditions. The time dependent shape evolution process and the conductivity measurement of the local reaction solution suggested that the spindle-like ZnO particles were formed at first and then the ring-like nanosheets grew heterogeneously on the backbone of these spindles. The ring-like nanosheets standing on the spindle-like rods was somewhat analogous to nacreous calcium carbonate layers around the columns near the growth tip of a young in red abalone, which could have some implications related with the formation of complex biominerals that exist in nature.

Ring-Like Nanosheets Standing on Spindle-Like Rods: Unusual ZnO Superstructures Synthesized from a Flakelike Precursor Zn5(OH)8Cl2·H2O

Nanostructured titania has been reported to be used in many applications in areas ranging from optics via solar energy to gas sensors. We report in this paper a low-cost method of producing nanostructured titania coatings. TiO 2 films were spin-coated on silicon substrates via methylcellulose (MC) aided aqueous sol–gel route using Ti(Obu t ) 4 –HAC–EtOH as starting materials. SEM, TGA, FTIR and XRD techniques were used to characterize the microstructure and properties of the composite films. It is shown that, relative dense, crack-free and transparent TiO 2 composite films (∼0.9 μm in thickness) were achieved via the MC assisted sol–gel and single-step deposition process at room temperature. TGA results showed the rapid decomposition of organic compounds in the composites at the range of 200–450 °C. Remarkable changes in microstructure of the composite film were observed after being heated at 600 °C for 15 min, including formation of a nodular morphology of TiO 2 particles (∼40 nm in diameter) within the films, appearance of crevice in nanoscale on the surface of the coating, and shrinkage of the films in thickness. It is worthy to note that the film uniformity was retained upon the heating; no cracks and flaking off from the substrates were observed. The structural evaluation and crystallization behavior with thermal treatment up to 900 °C are followed by FTIR and XRD.

Ke Jiang

Papers

Size-Dependent Photothermal Conversion Efficiencies of Plasmonically Heated Gold Nanoparticles

Size-Controllable Growth of Single Crystal In(OH)3 and In2O3 Nanocubes

Morphology control of stolzite microcrystals with high hierarchy in solution.

Ring-Like Nanosheets Standing on Spindle-Like Rods: Unusual ZnO Superstructures Synthesized from a Flakelike Precursor Zn5(OH)8Cl2·H2O

Sol–gel preparation of thick titania coatings aided by organic binder materials.