Controlled Modulation of the Structure and Luminescence Properties of Zero-Dimensional Manganese Halide Hybrids through Structure-Directing Metal-Ion (Cd2+ and Zn2+) Centers

Tunability of Photovoltaic Functions via Halogen Substitution [(Ade)2 CdX4](X = Cl, Br): A Class of Three-Dimensional Organic-Inorganic Hybrid Materials

Two new three-dimensional organic-inorganic hybrid crystalline materials, [(Ade)2 CdCl4] (1) and [(Ade)2 CdBr4] (2), were obtained by the slow evaporation of adenine (Ade) and cadmium chloride in aqueous solution at room temperature with hydrochloric acid and hydrobromic acid used as halogen sources. The structural, thermal, optical, and electrical properties were characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, variable-temperature-variable-frequency dielectric constant analysis, and electrochemical tests. With increasing the substitution of Cl by Br, the composition of the material changed and the space group shifted from P-1 to P21/m, with a significant blue-shift in the fluorescence emission. Changing the temperature induced the deformation of the three-dimensional framework structure formed by hydrogen bonding interactions, leading to dielectric anomalies. Cyclic voltammetry tests showed the good reversibility of the electrolysis process. The structural diversity of the complexes was realized by modulating the halogen composition, and a new method for designing novel organic-inorganic hybrids with controllable photoelectric functionality was proposed.

Achiral phosphonium induced remarkable circular polarized luminescence in a chiral cadmium(II) halide perovskite material

Circular polarized luminescence (CPL) sensitive two-dimensional organic inorganic halide perovskites have versatile applications in optical displays, encrypted transmission and quantum communications. Here, a new chiral hybrid [MePh3P]2CdCl4 (PCC) single crystal (SC) is synthesized using an achiral phosphonium cation by a solvent evaporation process at room temperature (rt). SC x-ray study reveals a non-centrosymmetric point group 23, with 21-screw optical axes providing a chiral Sohncke space group. Hirshfeld surface analysis suggests long-range H-bonding and ionic interactions (~ 3-9 kJ mol-1) and short-range Van der Waals and dispersion interactions (∼0.4-4 kJ mol-1). Both the PCC thin films and SCs exhibit prominent circular dichroism (CD) and remarkably superior CPL activity at rt (|gCD| ≈ 5 × 10-3 and |glum| ≈ 4.3 × 10-2).

Regulating the Optical Properties of Cs3MnBr5 Nanocrystals in Glasses for Narrow-Band Green Emission

Environmentally friendly phosphors with narrow-band green luminescence are in great demand for solid-state lighting and backlight display applications. Herein, all inorganic lead-free Cs3MnBr5 nanocrystals (NCs) are prepared in glass with dual-band luminescence and a high photoluminescence (PL) quantum yield of 60.2%. However, due to the short separation and strong coupling interaction between neighboring [ M n B r 4 ] 2 - units, Cs3MnBr5 NCs undergo energy transfer from a single [ M n B r 4 ] 2 - unit to coupled [ M n B r 4 ] 2 - clusters and give green-red dual-band PL. Incorporation of Zn into Cs3MnBr5 NCs therefore enlarges the average separation and reduces the interaction between neighboring [ M n B r 4 ] 2 - units to inhibit energy transfer from the green-emitting [ M n B r 4 ] 2 - unit to coupled [ M n B r 4 ] 2 - clusters, thus changing the dual-band PL into single-band green PL at 524 nm with a full width at half maximum of 47 nm and a maximal PL quantum yield of 50%. Low-temperature PL also demonstrates that partial replacement of Mn2+ ions by Zn2+ ions can further confine the exciton in the [ M n B r 4 ] 2 - unit and suppress the energy transfer. These Cs3MnBr5 NCs- and Zn/Cs3MnBr5 NCs-embedded glasses also possess good thermal, photo-, and chemical stabilities. These features demonstrate that these Cs3MnBr5 NCs- and Zn/Cs3MnBr5 NCs-embedded glasses have potential applications for efficient, environmental-friendly, and stable green phosphors in the fields of solid-state lighting and backlight display.

The Effects of Mono- and Bivalent Linear Alkyl Interlayer Spacers on the Photobehavior of Mn(II)-Based Perovskites

Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime-the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Improving the Chemical Stability of Narrow-Band Green-Emitting Manganese(II) Hybrid by Zn-Doping

Hybrid tetrahedral Mn(II)-based halides show great potential for narrow-band green emitters, which could be applied in the liquid crystal display field. However, the strategy to improve the chemical stability of tetrahedral Mn hybrids has not been fully investigated. Here, we demonstrate that Zn doping can be an effective route to significantly improve the stability of tetrahedral Mn hybrids under air conditions without compromising the luminous efficiency. A new bromide (ABI)₂MnBr₄ (ABI = 2-aminobenzimidazole) is synthesized, which exhibits a typical zero-dimensional structure with isolated [MnBr₄]^2- tetrahedra in the P1̅ space group. Under 450 nm excitation, a narrow-band green-emitting peak at 516 nm is observed with a full width at half maximum of 42 nm. It is indicated that spontaneous phase transition from the tetrahedral to octahedral motif occurs in this Mn hybrid driven by humidity, combined with the emission color change from green to red. Interestingly, this phase transition could be strongly suppressed by Zn doping with a very low doping amount (5%), leading to the significantly improved chemical stability of (ABI)₂MnBr₄ without reducing the photoluminescence quantum yield. Our work provides a simple and feasible strategy to enhance the chemical stability of the green-emitting (ABI)₂MnBr₄, and it may also be applicable for other tetrahedral Mn-based hybrids.