Morphologiekontrollierte Synthese von organometallischen Halogenidperowskiten mit inverser Opalstruktur

Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations: (CH3 NH3 )1-2y (NH3 (CH2 )2 NH3 )2y Pb1-y I3 (0≤y≤0.25)

Tuning the optical properties of MAPbI₃ (MA=methylammonium) is a key requirement to increase the efficiency of perovskite solar cells (PSCs). Simple precipitation from solution allows the partial substitution of MA in MAPbI₃ by H₃ NCH₂ CH₂ NH₃ (H₂ en). Surprisingly, there is 1:1 exchange of the monovalent cation MA by the dication H₂ en. The charge compensation results from a deficit of Pb²⁺ , leading to a series MA_1-2y (H₂ en)_2y Pb_1-y I₃ with 0≤y≤0.25. This model has been supported by single-crystal measurements and NMR investigations. The substitution results in a continuous shift of the band gap from 1.51 to 2.1 eV and a color change from black to orange-red. The H₂ en content stabilizes the cubic high-temperature (HT) form of MAPbI₃ . There is a linear correlation between band gap and unit cell volume. The substitution enables controlled band gap tuning because the extent of substitution is closely related to the applied MA:H₂ en ratio in solution.

A Two-Dimensional Ruddlesden-Popper Perovskite Nanowire Laser Array based on Ultrafast Light-Harvesting Quantum Wells

Miniaturized nanowire nanolasers of 3D perovskites feature a high gain coefficient; however, room-temperature optical gain and nanowire lasers from 2D layered perovskites have not been reported to date. A biomimetic approach is presented to construct an artificial ligh-harvesting system in mixed multiple quantum wells (QWs) of 2D-RPPs of (BA)₂ (FA)_n-1 Pb_n Br_3n+1 , achieving room-temperature ASE and nanowire (NW) lasing. Owing to the improvement of flexible and deformable characteristics provided by organic BA cation layers, high-density large-area NW laser arrays were fabricated with high photostability. Well-controlled dimensions and uniform geometries enabled 2D-RPPs NWs functioning as high-quality Fabry-Perot (FP) lasers with almost identical optical modes, high quality (Q) factor (ca. 1800), and similarly low lasing thresholds.

Facile Synthesis of Lanthanide (Ce, Eu, Tb, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm)-Doped LnF3 and LnOF Porous Sub-Microspheres with Multicolor Emissions

Monodisperse YF₃ and YOF porous sub-microspheres were synthesized by using a novel sacrificing template method with amorphous Y(OH)CO₃ ⋅x H₂ O as the precursors and the template. It was found that the size and shape were well maintained, and the condensed precursor was transformed into uniform porous structures after fluoridation. By fine-tuning the feed of the fluorine source, the final product could be converted from YF₃ to YOF. A possible growth mechanism is proposed for the uniform porous YF₃ structure and the porous yolk-shell-like YOF structure. The luminescence properties showed that the as-synthesized YF₃ :Ln³⁺ (Ln=Eu, Tb, Ce, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm) products exhibited strong multicolor emissions, which included down-/upconversion and energy-transfer processes. Additionally, YOX (X=Cl and Br) could be obtained if a different halogen source was used during calcination. However, the spheres were almost completely destroyed. Our novel synthetic route can also be extended to other lanthanide fluorides (REF₃ , RE=Gd, Lu), which may open a facile way to fabricate novel porous nanostructures.