In the world of semiconductors, organic–inorganic hybrid (OIH) halide perovskite is a new paradigm. Recently, a zealous effort has been made to design new lead-free perovskite-like OIH halides, such as perovskitoids and antiperovskites, for optoelectronic applications. In this context, we have synthesized a perovskitoid compound (Piperidinium)MnCl3 (compound 1) crystallizing in an orthorhombic structure with infinite one-dimensional (1D) chains of MnCl6 octahedra. Interestingly, this compound shows switchable dielectric property governed by an order–disorder structural transition. By controlling the stoichiometry of piperidine, we have synthesized an antiperovskite (Piperidinium)3Cl[MnCl4] (compound 2), the inverse analogue of a perovskite, consisting of zero-dimensional (0D) MnCl4 tetrahedra. This type of organic–inorganic hybrid antiperovskite halide is unique and scarce. Such a dissimilarity in lattice dimensionality and Mn2+ ion coordination ensues fascinating photophysical and magnetic properties. Compound 1 exhibits red emission with a photoluminescence quantum yield (PLQY) of ∼28%. On the other hand, the 0D antiperovskite compound 2 displays green emission with a higher PLQY of 54.5%, thanks to the confinement effect. In addition, the dimensionality of the compounds plays a vital role in the exchange interaction. As a result, compound 1 shows an antiferromagnetic ground state, whereas compound 2 is paramagnetic down to 1.8 K. This emerging structure–property relationship in OIH manganese halides will set the platform for designing new perovskites and antiperovskites.

We report a large Stokes shift and broad emission band in a Mn-based organic–inorganic hybrid halide, (guanidinium)6Mn3Br12 [GuMBr], consisting of trimeric units of distorted MnBr6 octahedra representing a zero-dimensional compound with a liquid like crystalline lattice. Analysis of the photoluminescence (PL) line width and Raman spectra reveals the effects of electron–phonon coupling, suggestive of the formation of Frenkel-like bound excitons. These bound excitons, regarded as the self-trapped excitons (STEs), account for the large Stokes shift and broad emission band. The excited-state dynamics was studied using femtosecond transient absorption spectroscopy, which confirms the STE emission. Further, this compound is highly emissive with a PL quantum yield of ∼50%. With chloride ion incorporation, we observe enhancement of the emissive properties and attribute it to the effects of intrinsic quantum confinement. Localized electronic states in flat bands lining the gap and their strong coupling with phonons are confirmed with first-principles calculations.

We report five new manganese and copper organic–inorganic hybrid (OIH) halides based on 1,4-diazabicyclo[2.2.2]­octane (DABCO: C6H12N2). The materials obtained have general formula (H2DABCO)­MX4·nH2O where M = Mn and Cu, X = Cl and Br, and n = 0, 1, and 4. The compounds (H2DABCO)­MnX4·4H2O (X = Cl and Br) crystallize in a chiral P212121 structure with unique zero-dimensional (0D) manganese octahedra, whereas anhydrous (H2DABCO)­MnBr4 exhibits a monoclinic crystal structure (space group P21/c) with isolated MnBr4 tetrahedra. While (H2DABCO)­MnCl4·4H2O is nonluminescent, the bromine analogue displays red emission with a photoluminescence quantum yield (PLQY) of 10.8%. Interestingly, anhydrous (H2DABCO)­MnBr4 demonstrates intense green emission due to the tetrahedral coordination of Mn2+ ion. The PLQY for (H2DABCO)­MnBr4 is 52.16%, and it shows a longer lifetime of the photoexcited electrons than the hydrated compound. In contrast, the copper OIH halides (X = Cl and Br) reveal an identical 0D tetrahedral structure crystallizing with one water molecule in the P21/c space group. Both manganese and copper OIH halides exhibit a magnetocaloric effect at low temperatures.

We report on the synthesis, structure, and photophysical properties of a lead-free organic−inorganic hybrid halide, (Piperidinium) 2 MnBr 4 (PipMBr). It crystallizes in a monoclinic P2 1 / n structure, with isolated MnBr 4 tetrahedra representing a zerodimensional compound. It undergoes a reversible isostructural transition at 422/417 K in the heating/cooling cycle owing to the hydrogen-bonding rearrangement mediated by ring puckering of piperidinium cations. This compound exhibits green emission with a photoluminescence quantum yield of 51%. Interestingly, strong electron-longitudinal optical phonon coupling with γ LO of 237 meV is evidenced from the broadening of the temperature-dependent emission linewidth and the Raman spectrum. Such strong electron−phonon coupling and a relatively low Debye temperature (137 K) suggest the self-trapped exciton emission in this compound.

Rare-earth ion-activated oxide phosphors are beneficial to overcome the problems like photobleaching, reduced lifetime, and the blinking of organic dyes and quantum dots for bioimaging applications. In this work, we...