Mingmei Wu

Bio: Mingmei Wu is an academic researcher from Sun Yat-sen University. The author has contributed to research in topics: Phosphor & Luminescence. The author has an hindex of 53, co-authored 209 publications receiving 9947 citations. Previous affiliations of Mingmei Wu include Qingdao University & University of St Andrews.

Mn2+ and Mn4+ red phosphors: synthesis, luminescence and applications in WLEDs. A review

Abstract: Transition-metal activated phosphors are an important family of luminescent materials that can produce white light with an outstanding color rendering index and correlated color temperature for use in light-emitting diodes. In recent years, work in this quite “hot” research field has focused on the development of Mn2+ and Mn4+ activated red phosphors. In this review article, we provide an overview of recent studies on Mn2+ and Mn4+ doped phosphors, including detailed synthesis routes (solid-state reaction and wet-chemical synthesis) and description of luminescence mechanisms and phosphors’ behaviors; discuss their promising applications in white light-emitting diodes; and present an extensive list of references to representative works in this field.

N-, O-, and S-Tridoped Carbon-Encapsulated Co9S8 Nanomaterials: Efficient Bifunctional Electrocatalysts for Overall Water Splitting

Abstract: The development of highly active and stable earth-abundant catalysts to reduce or eliminate the reliance on noble-metal based ones in green and sustainable (electro)chemical processes is nowadays of great interest. Here, N-, O-, and S-tridoped carbon-encapsulated Co9S8 (Co9S8@NOSC) nanomaterials are synthesized via simple pyrolysis of S- and Co(II)-containing polypyrrole solid precursors, and the materials are proven to serve as noble metal-free bifunctional electrocatalysts for water splitting in alkaline medium. The nanomaterials exhibit remarkable catalytic performances for oxygen evolution reaction in basic electrolyte, with small overpotentials, high anodic current densities, low Tafel slopes as well as very high (nearly 100%) Faradic efficiencies. Moreover, the materials are found to efficiently electrocatalyze hydrogen evolution reaction in acidic as well as basic solutions, showing high activity in both cases and maintaining good stability in alkaline medium. A two-electrode electrolyzer assembled using the material synthesized at 900 °C (Co9S8@NOSC-900) as an electrocatalyst at both electrodes gives current densities of 10 and 20 mA cm−2 at potentials of 1.60 and 1.74 V, respectively. The excellent electrocatalytic activity exhibited by the materials is proposed to be mainly due to the synergistic effects between the Co9S8 nanoparticles cores and the heteroatom-doped carbon shells in the materials.

Advanced red phosphors for white light-emitting diodes

Abstract: White light-emitting diodes (WLEDs) with high luminous brightness, low energy consumption, long lifetime and environmental friendliness can be applied in various fields. However, low colour rendering index and high correlated colour temperature have seriously limited the quality of white light, resulting from the deficiency of the red light component in commercial phosphors. New phosphors that can emit suitable red light are needed. The improvement of red emitters has gradually become a hot topic in WLED applications such as good colour rendering lighting and full colour displays. This review summarizes recent achievements concerning red phosphors mainly from three aspects. They are: intensifying absorption bands and reducing lattice defects to increase quantum efficiency; selecting an appropriate coordination environment and altering the lattice symmetry to fine-tune the luminescence spectra; and reducing the nonradiative transition rate and preventing charge imbalance of a luminescence centre to enhance thermal stability.

HF-Free Hydrothermal Route for Synthesis of Highly Efficient Narrow-Band Red Emitting Phosphor K2Si1–xF6:xMn4+ for Warm White Light-Emitting Diodes

Abstract: With superior photoluminescent properties, the recently discovered A2MF6:Mn4+ material holds the potential in replacing the commercial rare-earth-doped (oxy)nitride phosphors for solid state lighting and display. We report here a green synthetic route to synthesize narrow red emitting K2SiF6:Mn4+ without the usage of toxic and volatile HF solution. We show that K2SiF6:Mn4+ is produced in common low-toxic H3PO4/KHF2 liquid instead of high-toxic HF liquid and systematically investigate its morphology and photoluminescence properties. Moreover, the reaction mechanism is comprehensively discussed in detail. We find that not only does H3PO4/KHF2 play the same key roles as HF in the process of stabilizing Mn4+ and promoting Mn4+ into the host K2SiF6, but also it exhibits more excellent ability than HF in controlling the concentration of Mn4+ ion in the host K2SiF6. By demonstrating its application in white light-emitting diode (LED) with tunable chromaticity coordinate and correlated color temperature, we show ...

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Abstract: The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

Review of the anatase to rutile phase transformation

Abstract: Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

Upconversion Nanoparticles: Design, Nanochemistry, and Applications in Theranostics

Abstract: Applications in Theranostics Guanying Chen,*,†,‡ Hailong Qiu,†,‡ Paras N. Prasad,*,‡,§ and Xiaoyuan Chen* †School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China ‡Department of Chemistry and the Institute for Lasers, Photonics, and Biophotonics, University at Buffalo, State University of New York, Buffalo, New York 14260, United States Department of Chemistry, Korea University, Seoul 136-701, Korea Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892-2281, United States