David Enseling

Synthesis and optical properties of Li3Ba2La3(MoO4)8:Eu3+ powders and ceramics for pcLEDs

A series of polycrystalline Li3Ba2La3−xEux(MoO4)8 samples were prepared by the conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction measurements. The luminescence spectra and decay curves were studied as a function of Eu3+ concentration and temperature. It turned out that the optical band gap of the undoped molybdates is at 3.65 eV. The quantum efficiency (QE) of the Eu3+ doped luminescent materials increases with increasing Eu3+ concentration and almost 100% QE was obtained for those samples doped with 70, 80, or 90% Eu3+. A sample containing 100% Eu3+ showed solely a slight decrease in quantum efficiency. The luminous efficacy (LE) was 330 and 312 lm Wopt−1 for the 10 and 100% Eu3+ doped samples, respectively. The decrease of LE values is caused by a slight shift of the colour point to the red spectral range with increasing Eu3+ content. Temperature dependent measurements revealed that Li3Ba2Eu3(MoO4)8 loses only 15% of efficiency up to 400 K, which demonstrates that the investigated phosphors are attractive for application in pcLEDs.

Solid State Complex Chemistry: Formation, Structure, and Properties of Homoleptic Tetracyanamidogermanates RbRE[Ge(CN2)4] (RE = La, Pr, Nd, Gd)

Tetracyanamidometallates with the general formula RbRE[T(CN2)4] (RE = La, Pr, Nd, Gd; T = Si, Ge) were prepared by solid state metathesis reactions starting from stoichiometric mixtures of RECl3, A2[TF6], and Li2(CN2). Reactions were studied by differential thermal analysis that showed ignition temperatures between 360 and 390 °C for the formation of RbGd[T(CN2)4] with T = Si and Ge. The powder diffraction patterns of RbRE[Ge(CN2)4] were indexed isotypically to the already known RbRE[Si(CN2)4] compound. IR spectra of RbLa[Ge(CN2)4] were measured and compared with those of RbLa[Si(CN2)4]. (73)Ge, (87)Rb, and (139)La solid state NMR measurements and density functional theory calculations were used to verify the novel homoleptic [Ge(CN2)4](4-) ion. Luminescence properties of Eu(3+), Ce(3+), and Tb(3+) doped samples are reported.

A ligand substituted tungsten iodide cluster: luminescence vs. singlet oxygen production

Octahedral tungsten iodide clusters equipped with apical ligands (L) are synthesized to implement substantial photophysical properties. The [W6I8(CF3COO)6]2- cluster reported herein is the first example of a family of ligand substituted [W6I8L6]2- clusters. Such compounds are expected to exhibit a rich photochemistry in which the apical ligands play a crucial role. The versatile solid state and solution phase photophysical properties of (TBA)2[W6I8(CF3COO)6] described herein parallel characteristics obtained in some photophysically active organic compounds, including a broad absorption in the UV/VIS region. Upon irradiation of this compound, a broad red emission is observed in the VIS/NIR region resulting from excited triplet states, and singlet oxygen (a1Δg) is generated in the presence of O2.

Synthesis of new structurally related cyanamide compounds LiM(CN{sub 2}){sub 2} where M is Al{sup 3+}, In{sup 3+} or Yb{sup 3+}

Abstract New ternary cyanamide compounds isostructural to LiY(CN 2 ) 2 were obtained by solid state metathesis reaction. The crystal structure of LiAl(CN 2 ) 2 was determined by single crystal X-ray diffraction, the structures of LiIn(CN 2 ) 2 and LiYb(CN 2 ) 2 were solved from X-ray powder diffraction data. Photoluminescence properties of Tb 3+ -doped LiIn(CN 2 ) 2 are reported too.