Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Owing to the unique mechanism of photoelectron storage and release, long persistent phosphorescence, also called long persistent luminescence or long lasting afterglow/phosphorescence, plays a pivotal role in the areas of spectroscopy, photochemistry, photonics and materials science. In recent years, more research has focused on the manipulation of the morphology, operational wavebands and persistent duration of long persistent phosphors (LPPs). These desired achievements stimulated the growing interest in designing bio-labels, photocatalysts, optical sensors, detectors and photonic devices. In this review, we present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, materials system, and applications of LPPs. First, we introduce the recent developments in LPPs for the synthesis of nanoparticles from the aspects of particle sizes, monodispersity and homogeneity based on the urgent application of bio-imaging. In the later sections, we present the possible mechanisms, which involve the variation of trap distribution during the trapping and de-trapping process, complicated photo-ionization reaction of trap site levels and impurity centers together with their corresponding migration kinetics of carriers. Meanwhile, we emphasize the characterization techniques of defects, used to qualitatively or quantitatively describe the types, concentrations and depths of the traps. This review article also highlights the recent advances in suggested LPPs materials with a focus on the LPPs' hosts and optically active centers as well as their control, tuning and intrinsic links. We further discuss the classification of LPPs based on the different emission and excitation wavebands from the ultraviolet to the near-infrared region along with an overview of the activation mode of afterglow. Afterwards, we provide an exhibition of new products towards diverse application fields, including solar energy utilization, bio-imaging, diagnosis, and photocatalysts. Finally, we summarize the current achievements, discuss the problems and provide suggestions for potential future directions in the aforementioned parts.

Long persistent phosphors—from fundamentals to applications

Combustion synthesis of advanced materials: Part I. Reaction parameters

The synthesis of lanthanide-activated phosphors is pertinent to many emerging applications, ranging from high-resolution luminescence imaging to next-generation volumetric full-color display. In particular, the optical processes governed by the 4f-5d transitions of divalent and trivalent lanthanides have been the key to enabling precisely tuned color emission. The fundamental importance of lanthanide-activated phosphors for the physical and biomedical sciences has led to rapid development of novel synthetic methodologies and relevant tools that allow for probing the dynamics of energy transfer processes. Here, we review recent progress in developing methods for preparing lanthanide-activated phosphors, especially those featuring 4f-5d optical transitions. Particular attention will be devoted to two widely studied dopants, Ce3+ and Eu2+. The nature of the 4f-5d transition is examined by combining phenomenological theories with quantum mechanical calculations. An emphasis is placed on the correlation of hos...

Lanthanide-Activated Phosphors Based on 4f-5d Optical Transitions: Theoretical and Experimental Aspects.

Laser ablation synthesis in liquid solution (LASiS) is a “green” technique that gives access to the preparation of a library of nanomaterials. Bare noble metal spherical particles, multiphase core–shell oxides, metal–semiconductor heterostructures, layered organometallic compounds and other complex nanostructures can be obtained with the same experimental set up, just by varying a few synthetic parameters. How to govern such versatility is one of the current challenges of LASiS and requires a thorough understanding of the physical and chemical processes involved in the synthesis. In this perspective, the fundamental mechanisms of laser ablation in liquids are summarized, organized according to their temporal sequence and correlated with relevant examples taken from the library of nanomaterials disclosed by LASiS, in order to show how synthesis parameters influence the composition and the structure of products. The resulting framework suggests that, to date, much attention has been devoted to the physical aspects of laser–matter interaction and to the characterization of the final products of the synthesis. Conversely, the clarification of chemical processes active during LASiS deserves more research efforts and requires the synergy among multiple investigation techniques.

What controls the composition and the structure of nanomaterials generated by laser ablation in liquid solution

Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging.

https://www.mdpi.com/1996-1944/4/6/1132/pdf

Optical Properties of ZnO Nanoparticles Capped with Polymers.

Longer than 3-m ceramic-lined pipes can be produced by means of a thermit-reaction-induced process under the influence of a centrifugal force (“centrifugal-thermit process”). By igniting only a part of the reactant, the thermit reaction rapidly proceeds to provide a ceramic lining of homogeneous quality in the direction of the pipe length. As a result of the residual stress measurement of each layer forming the present ceramic-lined pipe, it is confirmed that the intermediate metal layer produced plays an important role in balancing the stress between the ceramic and outer pipe layers.

Long Ceramic‐Lined Pipes Produced by a Centrifugal‐Thermit Process

Onion-like carbon deposition by plasma spraying of nanodiamonds

A YVO4:Eu3+ colloid with an interesting nanostructure was formed by pulsed laser ablation in deionized water without any additives or surfactants. Analyses of particle morphology, composition and optical properties were accomplished by SEM, TEM, EDS PL and UV-vis. Ovoid-like particles formed by the agglomeration of numerous nanocrystals were observed by SEM and TEM, while EDS with area-mode analysis revealed that the content of dopant ion was well retained within the nanoparticles. In addition, the formation mechanism is deduced and discussed for the first time in this research. The findings of this study could provide new insights into the understanding of laser-induced oxide materials and offer an opportunity for other research groups to pursue red emitting nanophosphors with outstandingly purity.

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Facile and Chemically Pure Preparation of YVO4:Eu(3+) Colloid with Novel Nanostructure via Laser Ablation in Water.

Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binary glasses were synthesized in bulk form. Glass-forming region was found in the vicinity of eutectic point, which is approximately 29.5% LaO3/2 and 70.5% TiO2 in molar ratio. The glass transition temperature Tg and the crystallization onset temperature Tx of the obtained glasses were determined by differential scanning calorimetry. The thermal stability was evaluated by ΔT (=Tx − Tg). Our experimental results were compared with phase diagram of the LaO3/2–TiO2 binary system. Glass compositions with highest ΔT corresponded to single-phase compound of La4Ti9O24 and the eutectic point.

Osamu Odawara

Papers

Optical Properties of ZnO Nanoparticles Capped with Polymers.

Long Ceramic‐Lined Pipes Produced by a Centrifugal‐Thermit Process

Onion-like carbon deposition by plasma spraying of nanodiamonds

Facile and Chemically Pure Preparation of YVO4:Eu(3+) Colloid with Novel Nanostructure via Laser Ablation in Water.

Glass Formation in LaO3/2–TiO2 Binary System by Containerless Processing