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Single crystals of a new family of layered lanthanide oxychlorides, Ba3Ln2O5Cl2(Ln = Gd–Lu), have been synthesized from a molten barium flux. This family crystallizes in the space group I4/mmm(No. 139; Z= 2) with lattice parameters a= 4.3384(1)–4.4541(1) Å and c= 24.5108(7)–24.8448(9) Å. Ba3Ln2O5Cl2phases are built up of two different blocks: a perovskite double layer of stoichiometry Ba2Ln2O5formed by corner-connected LnO5tetragonal bipyramids and a puckered rock-salt-like interlayer of composition BaCl2. A complete structural study along with bond-valence-sum calculations shows that, for lanthanides larger than gadolinium, the structure becomes unstable. Density functional theory calculations show that the valence-band edge is dominated by oxygen orbitals, whereas the conduction band forms from Ba 5d orbitals. The synthesis of this family suggests a route to other potential multianion phases.

Organic–inorganic hybrid metal halide perovskites have emerged as a highly promising class of light emitters, which can be used as phosphors for optically pumped white light-emitting diodes (WLEDs). By controlling the structural dimensionality, metal halide perovskites can exhibit tunable narrow and broadband emissions from the free-exciton and self-trapped excited states, respectively. Here, we report a highly efficient broadband yellow light emitter based on zero-dimensional tin mixed-halide perovskite (C4N2H14Br)4SnBrxI6–x(x= 3). This rare-earth-free ionically bonded crystalline material possesses a perfect host-dopant structure, in which the light-emitting metal halide species (SnBrxI6–x4–, x= 3) are completely isolated from each other and embedded in the wide band gap organic matrix composed of C4N2H14Br–. The strongly Stokes-shifted broadband yellow emission that peaked at 582 nm from this phosphor, which is a result of excited state structural reorganization, has an extremely large full width at half-maximum of 126 nm and a high photoluminescence quantum efficiency of ∼85% at room temperature. UV-pumped WLEDs fabricated using this yellow emitter together with a commercial europium-doped barium magnesium aluminate blue phosphor (BaMgAl10O17:Eu2+) can exhibit high color rendering indexes of up to 85.