Nanosized Eu2+-doped AlN phosphor was successfully synthesized by a metal-organic precursor method for the first time. Aluminum and europium chlorides were simultaneously reacted with triethylamine in acetonitrile media to yield solid precipitates, which were transformed into nanosized AlN:Eu2+ phosphor powders upon calcination in an ammonia gas atmosphere. The possible reaction mechanism was proposed, which is in good agreement with the experimental results. The direct formation of Al–N bonds through a coordination reaction in solution is a key factor in the formation of well-crystallized AlN:Eu2+ grains at a moderately low temperature (1200 °C), which significantly suppresses abnormal grain growth and favors the formation of nanocrystalline (∼15 nm) particles with a homogeneous particle size distribution. Due to the homogeneous distribution of a relative high amount of Eu incorporation (2 wt%), the nanophosphors were effectively excited by UV light and featured an intense green emission band with a peak at 506 nm.

Electrons in topological insulators possess unique electronic band structures and spin properties, promising a novel route to engineer material properties for electronics and energy science. Enhancing the surface state signal in electron transport is critical for both fundamental study of the surface states and future applications. Nanostructures of topological insulators naturally have large surface-to-volume ratios, effectively increasing the surface transport compared to the bulk contribution. Moreover, the unique morphology of topological insulator nanostructures results in various quantum effects of electronic states, which can tailor the surface band via quantum confinement. Here we review recent progress in topological insulator nanostructures. Material design and electron transport of topological insulator nanostructures are introduced, with an emphasis on the unique properties of nanostructures. A few examples of applications and future perspective in using these nanostructures are also discussed.

Ternary semiconducting or metallic half-Heusler compounds with an atomic composition 1:1:1 are widely studied for their flexible electronic properties and functionalities. Recently, a new material property of half-Heusler compounds was predicted based on electronic structure calculations: the topological insulator. In topological insulators, the metallic surface states are protected from impurity backscattering due to spin-momentum locking. This opens up new perspectives in engineering multifunctional materials. In this article, we introduce half-Heusler materials from the crystallographic and electronic structure point of view. We present an effective model Hamiltonian from which the topological state can be derived, notably from a non-trivial inverted band structure. We discuss general implications of the inverted band structure with a focus on the detection of the topological surface states in experiments by reviewing several exemplary materials. Special attention is given to superconducting half-Heusler materials, which have attracted ample attention as a platform for non-centrosymmetric and topological superconductivity.

It is well established that symmetry has an important influence on the properties of materials, but the topology of electronic states might be an even more fundamental property. Topological insulators (TIs) are new states of matter based on the topology in the electronic band structure. Relativistic effects are the origin of the topologically non-trivial electronic structure, and the new state of matter has been realized in two-dimensional quantum well structures and three-dimensional bulk crystals of heavy elements and compounds. TI materials have an insulating gap in the bulk, and robust metallic edge/surface states on the boundary, which is robust against disorder and leads to unique spin and charge transport properties. Examples of TIs include HgTe/CdTe quantum wells, Bi-Sb-alloys, Bi2Se3, and half-Heusler compounds.

A wide class of materials that were discovered to carry a topologically protected phase order has led to a highly active area of research called topological insulators (TIs). This phenomenon has radically changed our thinking because of the robust quantum coherent behavior showing two-dimensional Dirac-type metallic surface states (SSs) and simultaneously insulating bulk states. The Dirac SSs are induced by the strong spin–orbit coupling as well as protected by time reversal symmetry (TRS). Breaking TRS in a TI with ferromagnetic perturbation can lead to many exotic quantum phenomena, such as the quantum anomalous Hall effect, topological magnetoelectric effect, as well as image magnetic monopole. This article presents an overview of the current status of TRS breaking in TIs and outlines the prospects for future studies.

The class of topological insulator materials is one of the frontier topics of condensed matter physics. The great success of this field is due to the conceptual breakthroughs in theories for topological electronic states and is strongly motivated by the rich variety of material realizations, thus making the theories testable, the experiments operable, and the applications possible. First-principles calculations have demonstrated unprecedented predictive power for material selection and design. In this article, we review recent progress in this field with a focus on the role of first-principles calculations. In particular, we introduce the Wilson loop method for the determination of topological invariants and discuss the band inversion mechanism for the selection of topological materials. Recent progress in quantum anomalous Hall insulators, large-gap quantum spin Hall insulators, and correlated topological insulators is also covered.