Group (III) Nitrides M[Mg 2Al2N4] (M: Ca, Sr, Ba, Eu) and Ba[Mg2Ga2N4]-Structural Relation and Nontypical Luminescence Properties of Eu 2+ Doped Samples. -The new compounds (V), (VIII), and (X) are characterized by powder and single crystal XRD, SEM, UV/VIS spectroscopy, and luminescence spectroscopy. All the compounds crystallize in space group I4/m with Z = 2 (UCr 4C4-type structure), forming highly condensed anionic networks of disordered (Al/Mg)N 4 and (Ga/Mg)N4 units, connected to each other by common edges and corners. M 2+ (M: Ca, Sr, Ba, Eu) is centered in vierer ring channels and cuboid-like coordinated by N. Eu 2+ doped samples of (VIIIa-c) exhibit nontypical luminescence properties including trapped exciton emission in the red spectral region. -(PUST, P.; HINTZE, F.; HECHT, C.; WEILER, V.; LOCHER, A.; ZITNANSKA, D.; HARM, S.; WIECHERT, D.; SCHMIDT, P. J.; SCHNICK*, W.; Chem. Mater. 26 (2014) 21, 6113-6119,
The highly efficient nitridosilicate phosphors M 2 Si 5 N 8 (M ) Sr, Ba, Eu) for phosphor-converted pcLEDs were synthesized at low temperatures using a novel precursor route involving metal amides M(NH 2 ) 2 . These precursors have been synthesized by dissolution of the respective metals in supercritical ammonia at 150°C and 300 bar. The thermal behavior and decomposition process of the amides were investigated with temperature programmed powder X-ray diffractometry and thermoanalytical measurements (DTA/ TG). These investigations rendered the amides as suitable intermediates for reaction with silicon diimide (Si(NH) 2 ). Thus, the desired nitridosilicate phosphors were obtained at relatively low temperatures around 1150-1400°C which is approximately 300°C lower compared to common synthetic approaches starting from metals or oxides. The influence of the thermal treatment on the phosphor morphology has been studied extensively. The accessibility of spherical phosphor particles represents another striking feature of this route since it improves light extraction from the crystallites due to decreasing light guiding and decreasing re-absorption inside the phosphor particle.
ABSTRACT:The alkaline earth nitridogallate Ba 3 Ga 3 N 5 was synthesized from the elements in a sodium flux at 760°C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba 3 Ga 3 N 5 (space group C2/c (No. 15), a = 16.801(3), b = 8.3301(2), c = 11.623(2) Å, β = 109.92(3)°, Z = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN 4 tetrahedra, each sharing two edges and at least one corner with neighboring GaN 4 units. There are three Ba 2+ sites with coordination numbers six or eight, respectively, and one Ba 2+ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu 2+ -doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm ). Ba 3 Ga 3 N 5 is the first nitridogallate for which parity allowed broadband emission due to Eu 2+ -doping has been found. The electronic structure of both Ba 3 Ga 3 N 5 as well as isoelectronic but not isostructural Sr 3 Ga 3 N 5 was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr 3 Ga 3 N 5 and 1.46 eV for Ba 3 Ga 3 N 5 .
Crystals of two new hexammoniates, namely, [Ga(NH3)6]I3·NH3 and [Ga(NH3)6]Br3·NH3, were grown from liquid ammonia solutions of GaI3 and GaBr3 in a wide temperature range. The known compound [Ga(NH3)5Cl]Cl2 and the new triammoniate of gallium fluoride Ga(NH3)3F3 were obtained ammonothermally during the synthesis of GaN from NH4Cl and NH4F, respectively. The compounds are characterized by crystallographic parameters derived from their X‐ray diffraction data. The crystal structures of all the ammoniates feature octahedrally coordinated Ga atoms in complex ions of the general form [Ga(NH3)6–nXn](3–n)+ (n = 0, 1, 2, 4; X = F, Cl, Br, I). The extensive N–H···X hydrogen bonding networks in these compounds are analyzed. The IR and Raman spectroscopy data for [Ga(NH3)6]X3·NH3 (X = Br, I) and Ga(NH3)2F3 are provided, and the IR spectrum of Ga(NH3)3F3 is compared with those published for the monoammoniate Ga(NH3)F3 and the diammoniate Ga(NH3)2F3. Finally, the thermal deamination features of [Ga(NH3)6]X3·NH3 (X = Br, I) and Ga(NH3)3F3 are also discussed.
The double nitride Mg 3 GaN 3 and binary nitride Mg 3 N 2 were synthesized from the elements by reaction with NaN 3 in a sodium flux. Reactions were carried out at 760 °C in welded shut tantalum ampules. Mg 3 GaN 3 was obtained as single crystals (space group R3̅ m (No. 166), a = 3.3939(5) Å and c = 25.854(5) Å, Z = 3, R1 = 0.0252, wR2 = 0.0616 for 10 refined parameters, 264 diffraction data points). This double nitride consists of an uncharged threedimensional network of MgN 4 and mixed (Mg/Ga)N 4 tetrahedra, which share common corners and edges. First-principles density functional theory (DFT) calculations predict Mg 3 GaN 3 to have a direct band gap of 3.0 eV, a value supported by soft X-ray spectroscopy measurements at the N K-edge. Eu 2+ -doped samples show yellow luminescence when irradiated with UV to blue light (λ max = 578 nm, full width at half maximum (fwhm) = 132 nm). Eu 2+ -doped samples of Mg 3 N 2 also show luminescence at room temperature when excited with ultraviolet (UV) to blue light. The maximum intensity of the emission band is found at 589 nm (fwhm = 145 nm).
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