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Low-dimensional halide perovskites exhibit intriguing excitonic properties and emerge as an important class of self-activated luminescent materials. However, the ability to manipulate and optimize their luminescent properties is limited by the lack of the microscopic understanding of the exciton relaxation and emission and the inconsistency in the theoretical results in the literature. In this work, based on first-principles calculations, we studied excitons in 1D lead halide perovskites, C4N2H14PbBr4 and C4N2H14PbCl4, which are both bright visible-light emitters. We find that, in both compounds, the polaron-pair exciton (EX-PP) is more stable than the onsite exciton (EX-OS) and only the EX-PP emission energy from the calculation is close to the main photoluminescence (PL) peak observed in the experiment. The EX-OS is found to emit UV light in both compounds. Therefore, the EX-PP is responsible for the experimentally observed visible light emission in both C4N2H14PbBr4 and C4N2H14PbCl4. Furthermore, the calculated small energy difference between the EX-PP and EX-OS in C4N2H14PbBr4 suggests that the metastable EX-OS can be thermally populated at room temperature (RT); the calculated EX-OS emission energy agrees well with the energy of a minor PL peak observed at RT but not at 77 K. The validity our approach in the exciton calculation is supported by the benchmark of the calculated exciton emission energies against the experimental results in 13 0D and 1D metal halides. The discrepancies between this work and a recent theoretical study in the literature are also discussed. [ABSTRACT FROM AUTHOR]

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue‐emitting all‐inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A2AgX3 (A = Rb, Cs; X = Cl, Br, I) through solid‐state synthesis is reported. In contrast to the Cu(I) analogs, A2AgX3 are broad‐band emitters sensitive to A and X site substitutions. First‐principle calculations show that defect‐bound excitons are responsible for the observed main PL peaks in Rb2AgX3 and that self‐trapped excitons (STEs) contribute to a minor PL peak in Rb2AgBr3. This is in sharp contrast to Rb2CuX3, in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A2AgX3 significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A2AgX3 are prepared and successfully used in anti‐counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A2AgX3 suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have recently enabled power conversion efficiency comparable to established technologies such as silicon and cadmium telluride. Ongoing efforts to improve the stability of halide perovskites in ambient air has yielded promising results. However, the presence of toxic heavy element lead (Pb) remains a major concern requiring further attention. Herein, we report three new Pb‐free hybrid organic–inorganic perovskite‐type halides based on gold (Au), (CH3NH3)AuBr4⋅H2O (1), (CH3NH3)AuCl4⋅H2O (2), and (CH3NH3)AuCl4 (3). Hydrated compounds 1 and 2 crystallize in a brand‐new structure type featuring perovskite‐derived 2D layers and 1D chains based on pseudo‐octahedral AuX6 building blocks. In contrast, the novel crystal structure of the solvent‐free compound 3 shows an exotic non‐perovskite quasi‐2D layered structure containing edge‐ and corner‐shared AuCl6 octahedra. The use of Au metal instead of Pb results in unprecedented low band gaps below 2.5 eV for single‐layered metal chlorides and bromides. Moreover, at room temperature the three compounds show a weak blue emission due to the electronic transition between Au‐6s and Au‐5d, in agreement with the density function theory (DFT) calculation results. These findings are discussed in the context of viability of Au‐based halides as alternatives for Pb‐based halides for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and characterization is reported of (C9NH20)2SnBr4, a novel organic metal halide hybrid with a zero‐dimensional (0D) structure, in which individual seesaw‐shaped tin (II) bromide anions (SnBr42−) are co‐crystallized with 1‐butyl‐1‐methylpyrrolidinium cations (C9NH20+). Upon photoexcitation, the bulk crystals exhibit a highly efficient broadband deep‐red emission peaked at 695 nm, with a large Stokes shift of 332 nm and a high quantum efficiency of around 46 %. The unique photophysical properties of this hybrid material are attributed to two major factors: 1) the 0D structure allowing the bulk crystals to exhibit the intrinsic properties of individual SnBr42− species, and 2) the seesaw structure enabling a pronounced excited state structural deformation as confirmed by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

In this work the Bridgman crystal growth and scintillation properties of both undoped and Tl-doped Cs 3 Cu 2 I 5 are presented. This material is very attractive for gamma and X-ray detection applications, with a density of 4.53 g/cm3 and effective atomic number of 51.9. Undoped Cs 3 Cu 2 I 5 had a light yield of 41,500 photons/MeV, with an energy resolution of 4.4% at 662 keV. Thallium doping at 0.5 mol % resulted in a much-improved scintillation response, in which light yield increased to 98,200 photons/MeV and energy resolution reduced to 3.3% at 662 keV. The X-ray excited emission is centered at 442 nm for the undoped and 500 nm for the Tl-doped crystals. The undoped emission is broad, typical of excitonic emission, while thallium doping results in an even broader band with features of both the undoped and thallium defect-mediated emissions. • Transparent single crystals of undoped Cs 3 Cu 2 I 5 and Cs 3 Cu 2 I 5 (Tl) were grown via the Bridgman technique. • Phase purity was established via powder XRD analysis. • Undoped Cs 3 Cu 2 I 5 has 41,500 photons/MeV and 4.4% energy resolution at 662 keV. • Tl doping at 0.5 mol% improves light yield to 98,200 photons/MeV and energy resolution to 3.3%. [ABSTRACT FROM AUTHOR]