The design and characterization of purely organic room-temperature phosphorescent (RTP) materials for optoelectronic applications is currently the focus of research in the field of organic electronics. Particularly, with the merits of preparation controllability and modulation flexibility, host-guest material systems are encouraging candidates that can prepare high-performance RTP materials. By regulating the interaction between host and guest molecules, it can effectively control the quantum efficiency, luminescent lifetime, and color of host-guest RTP materials, and even produce RTP emission with stimuli-responsive features, holding tremendous potential in diverse applications such as encryption and anti-counterfeiting, organic light-emitting diodes, sensing, optical recording, etc. Here a roundup of rapid achievement in construction strategies, molecule systems, and diversity of applications of host-guest material systems is outlined. Intrinsic correlations between the molecular properties and a survey of recent significant advances in the development of host-guest RTP materials divided into three systems including rigid matrix, exciplex, and sensitization are presented. Providing an insightful understanding of host-guest RTP materials and offering a promising platform for high throughput screening of RTP systems with inherent advantages of simple material preparation, low-cost, versatile resource, and controllably modulated properties for a wide range of applications is intended.

Recent Advances on Host-Guest Material Systems toward Organic Room Temperature Phosphorescence.

In addition to a bulk energy gap, topological insulators accommodate a conducting, linearly dispersed Dirac surface state. This state is predicted to become massive if time reversal symmetry is broken, and to become insulating if the Fermi energy is positioned inside both the surface and bulk gaps. We introduced magnetic dopants into the three-dimensional topological insulator dibismuth triselenide (Bi2Se3) to break the time reversal symmetry and further position the Fermi energy inside the gaps by simultaneous magnetic and charge doping. The resulting insulating massive Dirac fermion state, which we observed by angle-resolved photoemission, paves the way for studying a range of topological phenomena relevant to both condensed matter and particle physics.

http://absimage.aps.org/image/MAR11/MWS_MAR11-2010-000638.pdf

Massive Dirac Fermion on the Surface of a Magnetically Doped Topological Insulator

Rare earth equiatomic quaternary Heusler (EQH) compounds with chemical formula RXVZ (R = Yb, Lu; X = Fe, Co, Ni; Z = Al, Si) have recently attracted much attention since these materials are easily prepared and they also provide interesting properties for future spintronic applications. In this work, rare Earth-based EQH compounds in three types of structures are theoretically investigated through first-principles calculations based on density functional theory. We find that most of the studied rare Earth EQH compounds exhibit magnetic ground states including ferro-, antiferro-, and ferri-magnetic phases. Owing to the nearly closed shell f orbital in Lu and Yb, the spin magnetic moments mainly come from the 3d transition metal elements. In particular, in the type I structure, a large portion (7 out of 12) of EQH compounds are ferromagnetic half-metals (HMs) with integer magnetic moments ranging from 1 to 3 μB. In the type II structure, YbFeVAl is found to be a rare case of antiferro-magnetic (AFM) half-metal with zero total magnetic moments. Surprisingly, we also discover an unusual magnetic semiconductor LuCoVSi in the type III structure with a total spin magnetic moment of 3.0 μB and an indirect band gap of 0.2 eV. The structural and magnetic stabilities such as formation energy, magnetization energy as well as the mechanical stabilities such as the bulk, shear, and Young's moduli, and Poisson's, and Pugh's ratios of these EQH compounds are also investigated. Most of the studied compounds exhibit mechanical stability under the mechanical stability criteria and show elastic anisotropy. Our work provides guidelines for experimental researchers to synthesize useful materials in future spintronic applications.

/pdf/a-first-principles-study-of-rare-earth-quaternary-heusler-onxay7x0kl.pdf

A first-principles study of rare earth quaternary Heusler compounds: RXVZ (R = Yb, Lu; X = Fe, Co, Ni; Z = Al, Si)

We systematically investigate the topological band structures of half-Heusler compounds using first-principles calculations. The modified Becke-Johnson exchange potential together with local-density approximation for the correlation potential (MBJLDA) has been used here to obtain accurate band inversion strength and band order. Our results show that a large number of half-Heusler compounds are candidates for three-dimensional topological insulators. The difference between band structures obtained using the LDA and MBJLDA potential is also discussed.

/pdf/half-heusler-topological-insulators-a-first-principle-study-dqrqd6dycq.pdf

Half-Heusler Topological Insulators: A First-Principle Study with the Tran-Blaha Modified Becke-Johnson Density Functional

The development of organic room-temperature phosphorescence (RTP) materials with ultralong lifetimes is desired but remains challenging, especially those with blue RTP emission. Herein, through the cycloalkyl modification of phenothiazine-5,5-dioxide (CsO)...

Ultralong Blue Room-temperature Phosphorescence by Cycloalkyl Engineering

An overview on the structural diversity of europium based ternary intermetallics

Topological insulator (TI) materials which are conductive at the surface but insulating in the bulk have drawn much attention in the past decade due to their fascinating properties and potential application in the field of spintronics, quantum computing, topological superconductivity and next generation electronics In the search of three-dimensional TIs, half-Heusler compounds are the new entrants Half-Heusler compounds are equiatomic ternary compounds with cubic symmetry Due to the availability of a large pool of elements in the half Heusler family, the physical properties of these materials can be tuned by choosing the desired combination of elements In this perspective, we have briefly discussed the development of structural relations, the quantum hall effect, Landau quantization, and topological properties of a few representative systems in the half-Heusler family, including methods by which they are studied and characterized such as Angle Resolved Photoemission Spectroscopy, Shubnikov-de-Hass Oscillations and Nuclear Magnetic Resonance

Rare-earth based half-Heusler topological quantum materials: A perspective

Ambient, tunable room temperature phosphorescence from a simple phthalimide phosphor in amorphous polymeric matrix and in crystalline state

Electrical transport properties of half-heusler ScPdBi single crystals under extreme conditions

The structural and magnetic properties of Gd2−xNdxPdSi3 (x = 0, 0.75, 1, 2) have been studied using X-ray diffraction (XRD), exchange bias and magnetization measurements. The end compounds (x = 0, 2) along with the solid solutions of them are found to crystallize in the hexagonal superstructure having space group P6/mmc. The rare-earth (RE) ions are occupying at two different crystallographically inequivalent sites (2b and 6h), which is similar to all ordered members of the RE2PdSi3 series. The absence of chemical phase separation and formation of true solid solutions are confirmed by the XRD analysis. No signature of exchange bias has been observed signifying the absence of coexistence of magnetic phases. The origin of complex magnetic behaviour in Gd2−xNdxPdSi3 is observed due to the separate magnetic ordering and two available crystallographic sites for magnetic ion. The spin-glass behaviour near ferromagnetic transition in Nd2PdSi3 and anomalous bifurcation in zero-field-cooled and field-cooled magnetization curves in Gd2PdSi3 originates from the proximity and overlap of the transition temperatures of the two RE magnetic ions present in two inequivalent sites, and strongly correlated to the interatomic and intra-atomic distances between RE atoms occupying two crystallographic sites.

Ashutosh Kumar Singh

Papers

An overview on the structural diversity of europium based ternary intermetallics

Rare-earth based half-Heusler topological quantum materials: A perspective

Ambient, tunable room temperature phosphorescence from a simple phthalimide phosphor in amorphous polymeric matrix and in crystalline state

Electrical transport properties of half-heusler ScPdBi single crystals under extreme conditions

Structure and physical properties of the solid solution Gd2–xNdxPdSi3 (x = 0, 0.75, 1, 2)