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Title: Theoretical Study of Stability and Electronic Structure of Li(Mg,Zn)N Alloys: A Candidate for Solid State Lighting

Authors:
;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
940665
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 76; Journal Issue: 19, 2007; Related Information: Article No. 195208
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Materials Science and Semiconductors

Citation Formats

Walsh, A., and Wei, S. H. Theoretical Study of Stability and Electronic Structure of Li(Mg,Zn)N Alloys: A Candidate for Solid State Lighting. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.76.195208.
Walsh, A., & Wei, S. H. Theoretical Study of Stability and Electronic Structure of Li(Mg,Zn)N Alloys: A Candidate for Solid State Lighting. United States. doi:10.1103/PhysRevB.76.195208.
Walsh, A., and Wei, S. H. Mon . "Theoretical Study of Stability and Electronic Structure of Li(Mg,Zn)N Alloys: A Candidate for Solid State Lighting". United States. doi:10.1103/PhysRevB.76.195208.
@article{osti_940665,
title = {Theoretical Study of Stability and Electronic Structure of Li(Mg,Zn)N Alloys: A Candidate for Solid State Lighting},
author = {Walsh, A. and Wei, S. H.},
abstractNote = {},
doi = {10.1103/PhysRevB.76.195208},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 19, 2007,
volume = 76,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Using selective chemical mutation, we propose and investigate the electronic structure of an alloy with the potential to fill the green gap left open by existing InGaN based emission devices. The small mismatch between LiMgN and LiZnN, along with electronic band gaps spanning the visible range, makes them good candidates. Calculations are performed using a first-principles band structure method, with the special quasirandom structure approach employed to generate the random alloys. Comparison of LiMgN and LiZnN with their binary nitride analogs is made, and the energetic and electronic effects of alloy ordering are investigated. These alloys exhibit negative mixing enthalpiesmore » atypical of traditional binary nitride systems, which is explained in terms of the low lattice strain and the chemical bonding effects of the interstitial Li ions.« less
  • Results from crystal structural analyses of CuSb{sub 2}O{sub 6} with the trirutile structure, which transforms from the {beta} phase (space group P2{sub 1}/n) to the {alpha}-phase (space group P4{sub 2}/nmn) at 380 K, are reported. While extensive twinning prevents the single crystal structure determination of the {beta} modification, the {alpha} phase reveals compressed CuO{sub 6}polyhedra with Cu-O spacings of 202.6 pm (2x) and 206.6 pm (4x). From the spectroscopic investigation (EPR, optical) of mixed crystals Zn(Mg){sub 1-x}Cu{sub x}Sb{sub 2}O{sub 6} with dependence on x and temperature it is deduced that the CuO{sub 6} polyhedra are compressed (spacings {approx} 197 pmmore » (2x) and {approx} 208.5 pm (4x)) for x < 0.5 but transform to elongated entities at larger Cu{sup 2+} concentrations (spacings 200.4 pm (2x), 201.2 pm (2x), and 212.0 pm (2x) from neutron diffraction powder analysis (3)). Evidence for anisotropic {pi}-contributions to the Cu-O bond is presented. A detailed analysis of the ground state potential surface in terms of a vibronic Jahn-Teller coupling model in the presence of a host site strain is given for the two alternative CuO{sub 6} geometries. The Cu-O spacings in {alpha}-CuSb{sub 2}O{sub 6} are explained as resulting from those in the {beta} phase by a dynamic averaging process (201.2 pm (2x), 212.0 pm (2x) {yields} 206.6 pm (4x) above 380 K).« less
  • Ce{sup 3+}-doped and Ce{sup 3+}/Li{sup +}-codoped SrAlSi{sub 4}N{sub 7} phosphors were synthesized by gas pressure sintering of powder mixtures of Sr{sub 3}N{sub 2}, AlN, α-Si{sub 3}N{sub 4}, CeN and Li{sub 3}N. The phase purity, electronic crystal structure, photoluminescence properties of SrAlSi{sub 4}N{sub 7}:Ce{sup 3+}(Ce{sup 3+}/Li{sup +}) were investigated in this work. The band structure calculated by the DMol{sup 3} code shows that SrAlSi{sub 4}N{sub 7} has a direct band gap of 3.87 eV. The single crystal analysis of Ce{sup 3+}-doped SrAlSi{sub 4}N{sub 7} indicates a disordered Si/Al distribution and nitrogen vacnacy defects. SrAlSi{sub 4}N{sub 7} was identified as a majormore » phase of the fired powders, and Sr{sub 5}Al{sub 5}Si{sub 21}N{sub 35}O{sub 2} and AlN as minor phases. Both Ce{sup 3+} and Ce{sup 3+}/Li{sup +} doped SrAlSi{sub 4}N{sub 7} phosphors can be efficiently excited by near-UV or blue light and show a broadband yellow emission peaking around 565 nm. A highest external quantum efficiency of 38.3% under the 450 nm excitation was observed for the Ce{sup 3+}/Li{sup +}-doped SrAlSi{sub 4}N{sub 7} (5 mol%). A white light LED lamp with color temperature of 6300 K and color rendering index of Ra=78 was achieved by combining Sr{sub 0.97}Al{sub 1.03}Si{sub 3.997}N/94/maccounttest14=t0005{sub 1}8193 {sub 7}:Ce{sup 3+}{sub 0.03} with a commercial blue InGaN chip. It indicates that SrAlSi{sub 4}N{sub 7}:Ce{sup 3+} is a promising yellow emitting down-conversion phosphor for white LEDs. - Graphical abstract: One-phosphor converted white light-emitting diode (LED) was fabricated by combining a blue LED chip and a yellow-emitting SrAlSi4N7:Ce{sup 3+} phosphor (see inset), which has the color rendering index of 78 and color temperature of 6300 K. - Highlights: • We reported a new yellow nitride phosphor suitable for solid state lighting. • We solved the crystal structure and evidenced a disordered Si/Al distribution. • We fabricated a high color rendering white LEDs by using a single SrAlSi4N7:Ce.« less
  • M-DNA is a type of metalated DNA that forms at high pH and in the presence of Zn, Ni, and Co, with the metals placed in between each base pair, as in G-Zn-C. Experiments have found that M-DNA could be a promising candidate for a variety of nanotechnological applications, as it is speculated that the metal d-states enhance the conductivity, but controversy still clouds these findings. In this paper, we carry out a comprehensive ab initio study of eight G-Zn-C models in the gas phase to help discern the structure and electronic properties of Zn-DNA. Specifically, we study whether amore » model prefers to be planar and has electronic properties that correlate with Zn-DNA having a metallic-like conductivity. Out of all the studied models, there is only one which preserves its planarity upon full geometry optimization. Nevertheless, starting from this model, one can deduce a parallel Zn-DNA architecture only. This duplex would contain the imino proton, in contrast to what has been proposed experimentally. Among the nonplanar models, there is one that requires less than 8 kcal/mol to flatten (both in gas and solvent conditions), and we propose that it is a plausible model for building an antiparallel duplex. In this duplex, the imino proton would be replaced by Zn, in accordance with experimental models. Neither planar nor nonplanar models have electronic properties that correlate with Zn-DNA having a metallic-like conductivity due to Zn d-states. To understand whether density functional theory (DFT) can describe appropriately the electronic properties of M-DNAs, we have investigated the electronic properties of G-Co-C base pairs. We have found that when self-interaction corrections (SIC) are not included the HOMO state contains Co d-levels, whereas these levels are moved below the HOMO state when SIC are considered. This result indicates that caution should be exercised when studying the electronic properties of M-DNAs with functionals that do not account for strong electronic correlations.« less
  • The structure of the [eta][prime] phase, one of the most important age-hardening precipitates in commercial Al-Zn-Mg alloys, has been studied at the atomic level by means of high-resolution electron microscopy (HREM). A structural model of the [eta][prime] phase has been constructed on the basis of the structural characteristics in the observed images and the structure of the [eta]-MgZn[sub 2] phase. Image simulation of this model shows a good agreement between calculated and experimental images. Comparison of this model with the early existing model on the basis of the X-ray diffraction is also given.