The preparation of
cerium-substituted barium lutetium borate, Ba2Lu5B5O17:Ce3+,
is achieved using high temperature solid state synthesis. This compound
crystallizes in the Ba2Y5B5O17-type structure and shows an efficient blue emission (λmax = 447 nm) when excited by UV-light (λex = 340 nm) with a photoluminescent quantum yield near 90%, a fast
luminescence decay time (<40 ns), and a thermal quenching temperature
of 452 K. Further, preparing a solid solution following Ba2(Y1–x
Lu
x
)5B5O17:Ce3+ (x = 0, 0.25, 0.50, 0.75, 1) confirms that all compounds
are isostructural and follow Vegard’s law. Substituting Y3+ for Lu3+ yields a nearly constant emission spectrum
that blue-shifts by only 9 nm and has a consistent luminescence lifetime
across the range prepared. The photoluminescent quantum yield (PLQY)
and thermal quenching (T
50) of the solid
solution, however, are dramatically impacted by the composition, with
the PLQY decreasing to ≈70% and the T
50 dropping 49 K going from x = 1 to x = 0. These significant changes in the optical properties
likely stem from enhanced structural rigidity as the larger, more
polarizable Y3+ is substituted for the smaller, harder
Lu3+ cation. These results highlight the importance of
optimizing chemical bonding to improve a phosphor’s optical
properties.
The quinary members of the complex boride series Sc 2 FeRu 5−x Ir x B 2 were synthesized by arc melting the elements and characterized by powder and single-crystal X-ray diffraction as well as metallographic and energy-dispersive Xray analyses. The use of a 4d/5d mixture allows distinguishing these elements with X-ray diffraction methods, thus enabling the study of site preference and its influence on the magnetic properties. The magnetic measurements reveal several changes of magnetic ordering within the series: from antiferromagnetism (Sc 2 FeRu 5 B 2 ) to ferromagnetism (Sc 2 FeRuIr 4 B 2 ) and finally to metamagnetism (Sc 2 FeIr 5 B 2 ). Within the quinary series, the magnetic moments continuously increase with increasing amounts of Ir in one (8j) of two possible Wyckoff sites. The members with x = 2 and 3 represent the first hard magnetic borides of transition metals.
Now we are six: Planar B6 rings embedded in one‐dimensional Ti7 wheels have been found in the crystal structure of a solid‐state phase (Ti7Rh4Ir2B8) for the first time. First‐principles calculations indicated strong BB bonding but also significant interactions with the surrounding titanium atoms (see picture).
The
crystal structure of a novel barium yttrium borate, Ba2Y5B5O17, was determined using
a combination of ab initio global optimization algorithms and density
functional theory calculations along with Rietveld refinement of high-resolution
synchrotron X-ray powder diffraction data. Synthesized using a high-temperature
solid-state route, the structure consists of edge- and corner-sharing
Y- and Ba-centered polyhedra along with BO3 trigonal planes.
Ba and Y occupy four crystallographically independent sites with two
fully occupied by Y and two having a statistical mixture of Y and
Ba. Substituting Ce3+ into the structure for Y3+ yields blue photoluminescence (λem = 443 nm) upon
excitation with UV (λem = 365 nm) light. The emission
of this new compound is efficient with an external quantum yield of
70% and is stable as a function of temperature with a quenching temperature
of ≈400 K.
Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.
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