This paper provides a brief review of current research activities that focus on the fabrication of ceramic nanofibers by electrospinning, as well as their applications in various areas. We begin with a brief introduction to electrospinning in the context of ceramic nanofibers, and the methods for preparing aligned and/or hollow nanofibers. We then discuss approaches to the fabrication of nanofibers with a hierarchical structure. We continue with a highlight of some recent applications enabled by electrospun ceramic nanofibers, with a focus on three areas: catalysis, environmental science, and energy technology, which are expected to become the most important and exciting subjects of research in this century. In the end, we conclude this review with some perspectives on the future directions and implications for this new class of functional nanomaterials. Copyright © 2010 John Wiley & Sons, Ltd.

Ceramic nanofibers fabricated by electrospinning and their applications in catalysis, environmental science, and energy technology

One-dimensional LaOCl: Ln(3+) (Ln(3+) = Eu3+/Sm3+, Tb3+, Tm3+) nanofibers, nanotubes, and quasi-1D microbelts are successfully prepared by a sol-gel/electrospinning process. XRD, FT-IR, SEM, TEM, as well as photoluminescence (PL) and cathodoluminescecne (CL) spectra are used to characterize the resulting samples. Through a heat treatment process at high temperature, the as-prepared samples are well-crystallized with the tetragonal structure of LaOCl. Under ultraviolet radiation and low-voltage electron beam excitation, the LaOCl: Eu3+, LaOCl: Sm3+, LaOCl: Tb3+, and LaOCl: Tm3+ samples give the characteristic transitions of Eu3+ (D-5(0, 1, 2) -> F-7(0, 1, 2, 3, 4)), Sm3+ ((4)G(5/2) -> H-6(5/2,) (7/2,) (9/2)), Tb3+ (D-5(3, 4) -> F-7(2, 3, 4, 5, 6)), and Tm3+ (D-1(2), (1)G(4) -> F-3(4), H-3(6)), respectively. Moreover, there exists simultaneous luminescence of Tb3+, Tm3+, Eu3+, or Sm3+ individually when codoping them in the single-phase LaOCl host (for example, LaOCl: Tb3+, Eu3+/Sm3+ ; LaOCl: Tm3+, Eu3+/Sm3+; LaOCl: Tb3+, Tm3+, Eu3+/Sm3+ systems), which is beneficial to tune the emission colors. Under low-voltage electron beam excitation (1-5 kV), a variety of colors can be efficiently adjusted in a wide triangle region enveloped by three CIE chromaticity coordinate points [LaOCl: Eu3+, (x = 0.6039, y = 0.3796); LaOCl: Tb3+, (x = 0.2452, y = 0.5236); LaOCl: Tm3+, (x = 0.1456, y = 0.0702)] for mono- and co-doped LaOCl: Ln(3+) (Eu3+, Sm3+, Tb3+, Tm3+) samples, making these materials have potential applications in field-emission display devices.

Electrospinning Derived One‐Dimensional LaOCl: Ln3+ (Ln = Eu/Sm, Tb, Tm) Nanofibers, Nanotubes and Microbelts with Multicolor‐Tunable Emission Properties

Nowadays there are several technologies used for flat panel displays (FPDs) and the development of FPDs with enhanced energy efficiency and improved display quality is strongly required. Field emission displays (FEDs) have been considered as one of the most promising next generation flat panel display technologies due to their excellent display performance and low energy consumption. For the development of FEDs, phosphors are irreplaceable components. In the past decade, the study of highly efficient low-voltage cathodoluminescent materials, namely FED phosphors, has become the focus of enhancing energy efficiency and realizing high-quality displays. This review summaries the recent progress in the chemical synthesis and improvement of novel, rare-earth and transition metal ions activated inorganic cathodoluminescent materials in powder and thin film forms. The discussion is focused on the modification of morphology, size, surface, composition and conductivity of phosphors and the corresponding effects on their cathodoluminescent properties. Special emphases are given to the selection of host and luminescent centers, the adjustment of emission colors through doping concentration optimization, energy transfer and mono- or co-doping activator ions, the improvement of chromaticity, color stability and color gamut as well as the saturation behavior and the degradation behavior of phosphors under the excitation of a low-voltage electron beam. Finally, the research prospects and future directions of FED phosphors are discussed with recommendations to facilitate the further study of new and highly efficient low-voltage cathodoluminescent materials.

Recent progress in low-voltage cathodoluminescent materials: synthesis, improvement and emission properties

This feature article highlights the recent advances on the preparation, characteristics and application of one-dimensional (1D) luminescent materials (including rare earth based inorganic materials, rare earth based composite materials and non rare earth materials) by an electrospinning process. Electrospinning is an effective method to prepare 1D polymer, composite and inorganic submicro- or nano-materials. The key strategy of the electrospinning method is to form an electrospinning solution with viscoelastic behavior similar to that of a conventional polymer solution. It utilizes an electrical force on the surface of an electrospinning solution to overcome the surface tension and produce a very thin charged jet. This jet moves straight for a certain distance, and then bends into looping and spiraling paths. During the elongation of the liquid jet, solvent evaporates and 1D hybrid materials accumulate on a grounded collector. Dispersing complexes or inorganic nanoparticles into polymer and inorganic matrices, composite luminescent materials viaelectrospinning combine both inorganic and organic characters. Annealing the inorganic/polymer hybrid precursors can yield various kinds of inorganic luminescent materials with fiber, wire, belt and tube-like morphologies, which have potential applications in fluorescent lamps and color displays. Furthermore, with the addition of some surfactants, it is possible to prepare 1D luminescent and porous multifunctional materials, which can act as potential drug carriers in the biomedical area.

One-dimensional luminescent materials derived from the electrospinning process: preparation, characteristics and application

Recently, with the increased attention to indoor air quality, antimicrobial air filtration techniques have been studied widely to inactivate hazardous airborne microorganisms effectively. In this study, we demonstrate herbal extract incorporated (HEI) nanofibers synthesized by an electrospinning technique and their application to antimicrobial air filtration. As an antimicrobial herbal material, an ethanolic extract of Sophora flavescens, which exhibits great antibacterial activity against pathogens, was mixed with the polymer solution for the electrospinning process. We measured various characteristics of the synthesized HEI nanofibers, such as fiber morphology, fiber size distribution, and thermal stability. For application of the electrospun HEI nanofibers, we made highly effective air filters with 99.99% filtration efficiency and 99.98% antimicrobial activity against Staphylococcus epidermidis. The pressure drop across the HEI nanofiber air filter was 4.75 mmH2O at a face air velocity of 1.79 cm/s. These results will facilitate the implementation of electrospun HEI nanofiber techniques to control air quality and protect against hazardous airborne microorganisms.

Herbal Extract Incorporated Nanofiber Fabricated by an Electrospinning Technique and its Application to Antimicrobial Air Filtration.

One-dimensional Pr3+-doped CaTiO3 microfibers were fabricated by a simple and cost-effective electronspinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential analysis (TG-DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), quantum efficiency (QE), and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. Under ultraviolet excitation and low-voltage electron beams (1-3 kV) excitation, the CaTiO3:x Pr3+ samples show the red emission at 612 nm, corresponding to 1D2-3H4 transition of Pr3+. The luminescence intensity, quantum efficiency, and the lifetime have been studied as a function of the doping concentration of Pr3+ in the CaTiO3 samples.

Synthesis and luminescent properties of CaTiO3: Pr3+ microfibers prepared by electrospinning method

Gd2MoO6:Eu3+ nanofibers and nanobelts have been prepared by a combination method of the sol-gel process and electrospinning. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy, photoluminescence, and low voltage cathodoluminescence as well as kinetic decays were used to characterize the resulting samples. The results of XRD and FTIR indicate that the Gd2MoO6:Eu3+ samples have crystallized at 600 degrees C with the monoclinic (alpha) structure. The SEM and TEM results indicate that the as-formed precursor fibers and belts are uniform and that the as-prepared nanofibers and nanobelts consist of nanoparticles. Gd2MoO6:Eu3+ phosphors show their strong characteristic emission under UV excitation (353 nm) and low voltage electron-beam excitation (3 kV), making the materials have potential applications in fluorescent lamps and field-emission displays.

Sensors and Displays: Principles, Materials, and Processing - Preparation and Luminescence Properties of Gd2MoO6:Eu3+ Nanofibers and Nanobelts by Electrospinning

Cuimiao Zhang

Papers

Synthesis and luminescent properties of CaTiO3: Pr3+ microfibers prepared by electrospinning method

Sensors and Displays: Principles, Materials, and Processing - Preparation and Luminescence Properties of Gd2MoO6:Eu3+ Nanofibers and Nanobelts by Electrospinning