The structural, optical, and magnetic properties of the vacancy-ordered quadruple perovskites Cs 4 CdBi 2 Cl 12 and Cs 4 MnBi 2 Cl 12 and their solid solution have been investigated. Both compounds crystallize with the R3̅ m space group symmetry that arises from the ordering of Bi 3+ , Mn 2+ /Cd 2+ , and cation vacancies into layers that run perpendicular to the ⟨111⟩ direction of the cubic perovskite structure. Cs 4 MnBi 2 Cl 12 is paramagnetic down to 2 K with a Weiss constant of −2.88(3) K and an effective moment of 5.840(1) μ B . This compound exhibits weak orange-red luminescence, which involves Bi 3+ ions absorbing near-UV photons, followed by energy transfer to Mn 2+ ions and finally radiative decay that is attributed to a spin-forbidden 4 T 1 (G) → 6 A 1 (S) d−d transition. The emission peak is centered near 605 nm with a fullwidth at half-maximum of ∼90 nm and a photoluminescence quantum yield (PLQY) of ∼4%. The isostructural Cs 4 CdBi 2 Cl 12 is neither magnetic nor does it show detectable PL at room temperature. Replacing Mn 2+ with Cd 2+ to form Cs 4 Cd 1−x Mn x Bi 2 Cl 12 leads to a zero-dimensional electronic structure that inhibits energy migration to defect sites where nonradiative decay can occur, increasing the room temperature PLQY to 57% in the x = 0.27 sample. Cs 4 Cd 1−x Mn x Bi 2 Cl 12 phosphors are easily synthesized from solution, do not contain rare-earth ions, and possess emission spectra that compare favorably to narrow band, red phosphors containing Eu 2+ .

Here, we present the synthesis and crystal structure of Rb3InCl6 prepared from air stable reagents via a two-step process that proceeds through the intermediate Rb2InCl5·H2O. Rb3InCl6 crystallizes with the Rb3YCl6 structure type (C2/c), which can be derived from the double perovskite structure by noncooperative tilting of isolated [InCl6]3– octahedra. Despite this lowering of symmetry, the optical properties are similar to the cubic double perovskite Cs2NaInCl6. Partial substitution of In3+ with Sb3+ in Rb3InCl6 results in intense cyan-green photoluminescence originating from localized 5s2 to 5s15p1 electronic transitions of [SbCl6]3– polyatomic anions. In comparison with the cubic double perovskite phosphor Cs2NaInCl6:Sb3+, the octahedral tilting distortion increases the electronic isolation of the In/Sb-centered octahedra thus facilitating electron and hole localization on Sb3+ sites, leading to bright photoluminescence. The distorted crystal structure also leads to a larger Stokes shift (1.29 eV) and a corresponding red shift of the emission peak (λmax = 522 nm) compared to the more symmetric Cs2NaInCl6:Sb3+ (Stokes shift ≈ 0.94 eV, λmax = 445 nm).

The structural and optical properties of the halide substitutions of Br − and I − into Cs 4 M II M III 2 Cl 12 (M II = Cd 2+ , Mn 2+ ; M III = Bi 3+ , Sb 3+ ) have been investigated. All compositions adopt the ⟨111⟩ layered vacancy-ordered quadruple perovskite structure with R3̅ m space group symmetry. Through incremental halide substitution reactions, we show that significant bromide incorporation is possible (>25% for Cd 2+ -containing structures). The larger halide ions (Br − or I − ) preferentially occupy the anion sites adjacent to the cation-vacancy layer. In those compositions where M II is Cd 2+ , incorporation of bromide ions leads to substantial M II /vacancy antisite disorder, which is accompanied by a more even distribution of bromide substitution over the two chemically distinct anion sites. The Cs 4 CdM III 2 Cl 12 compounds can incorporate over twice the amount of bromide as analogous Mn 2+ -containing compounds, with a maximum of 29(2)% bromide substitution found for Cs 4 CdSb 2 Cl 12 . Iodide incorporation is more limited, with a maximum of ∼6% halide substitution for Cs 4 CdBi 2 Cl 12 . The incorporation of the heavier, less electronegative Br − and I − ions results in a red shift of the onset of optical absorption in a Vegard's Law type fashion. The effect is largest for Cs 4 CdBi 2 Cl 12−z X z , where the absorption onset shifts from 3.20(1) eV to 2.99(1) eV as the composition changes from Cs 4 CdBi 2 Cl 12 to Cs 4 CdBi 2 Cl 8.9 Br 3.1 . As discussed in the paper, these results offer some insights into the factors that stabilize the vacancy-ordered quadruple perovskite structure.

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A symmetry mode analysis yields 47 symmetrically distinct patterns of octahedral tilting in hybrid organic–inorganic layered perovskites that adopt the n = 1 Ruddlesden–Popper (RP) structure. The crystal structures of compounds belonging to this family are compared with the predictions of the symmetry analysis. Approximately 88% of the 140 unique structures have symmetries that agree with those expected based on octahedral tilting alone, while the remaining compounds have additional structural features that further lower the symmetry, such as asymmetric packing of bulky organic cations, distortions of metal-centered octahedra or a shift of the inorganic layers that deviates from the a/2 + b/2 shift associated with the RP structure. The structures of real compounds are heterogeneously distributed amongst the various tilt systems, with only 9 of the 47 tilt systems represented. No examples of in-phase ψ-tilts about the a and/or b axes of the undistorted parent structure were found, while at the other extreme ∼66% of the known structures possess a combination of out-of-phase ϕ-tilts about the a and/or b axes and θ-tilts (rotations) about the c axis. The latter combination leads to favorable hydrogen bonding interactions that accommodate the chemically inequivalent halide ions within the inorganic layers. In some compounds, primarily those that contain either Pb2+ or Sn2+, favorable hydrogen bonding interactions can also be achieved by distortions of the octahedra in combination with θ-tilts.