Zero-Dimensional Broadband Yellow Light Emitter (TMS)3Cu2I5 for Latent Fingerprint Detection and Solid-State Lighting.

We report a new hybrid organic-inorganic Cu(I) halide, (TMS)3Cu2I5 (TMS = trimethylsulfonium), which demonstrates high efficiency and stable yellow light emission with a photoluminescence quantum yield (PLQY) over 25%. The zero-dimensional crystal structure of the compound is comprised of isolated face-sharing photoactive [Cu2I5]3- tetrahedral dimers surrounded by TMS+ cations. This promotes strong quantum confinement and electron-phonon coupling, leading to a highly efficient emission from self-trapped excitons. The hybrid structure ensures prolonged stability and nonblue emission compared to unstable blue emission from all-inorganic copper(I) halides. Substitution of Cu with Ag leads to (TMS)AgI2, which has a one-dimensional chain structure made of edge-sharing tetrahedra, with weak light emission properties. Improved stability and highly efficient yellow emission of (TMS)3Cu2I5 make it a candidate for practical applications. This has been demonstrated through utilization of (TMS)3Cu2I5 in white light-emitting diode with a high Color Rendering Index value of 82 and its use as a new luminescent agent for visualization of in-depth latent fingerprint features. This work illuminates a new direction in designing multifunctional nontoxic hybrid metal halides.

Magnetic structures and excitations in sawtooth olivine chalcogenides Mn2SiX4 (X = S, Se).

The Mn lattice in olivine chalcogenide Mn2SiX4 (X = S, Se) compounds forms a sawtooth, which is of special interest in magnetism owing to the possibility of realizing flat bands in magnon spectra, a key component in magnonics. In this work, we investigate the Mn2SiX4 olivines using magnetic susceptibility, and X-ray and neutron diffraction. We have determined the average and local crystal structures of Mn2SiS4 and Mn2SiSe4 using synchrotron X-ray, neutron diffraction, and X-ray total scattering data followed by Rietveld and pair distribution function analyses. It is found from the pair distribution function analysis that the Mn triangle that constitutes the sawtooth is isosceles in Mn2SiS4 and Mn2SiSe4. The temperature evolution of magnetic susceptibility of Mn2SiS4 and Mn2SiSe4 shows anomalies below 83 K and 70 K, respectively, associated with magnetic ordering. From the neutron powder diffraction measurements the magnetic space groups of Mn2SiS4 and Mn2SiSe4 are found to be Pnma and Pnm'a', respectively. We find that the Mn spins adopt a ferromagnetic alignment on the sawtooth in both Mn2SiS4 and Mn2SiSe4 but along different crystallographic directions for the S and the Se compounds. From the temperature evolution of Mn magnetic moments obtained from refining neutron diffraction data, the transition temperatures are accurately determined as TN(S) = 83(2) K and TN(Se) = 70.0(5) K. Broad diffuse magnetic peaks are observed in both the compounds, and are prominently seen close to TN, suggesting the presence of a short-range magnetic order. The magnetic excitations studied using inelastic neutron scattering reveal a magnon excitation with an energy corresponding to approximately 4.5 meV in both S and Se compounds. Spin correlations are observed to persist up to 125 K much above the ordering temperature and we suggest the possibility of short-range spin correlations responsible for this.

Investigation of the Solution Chemistry of Hybrid Organic-Inorganic Indium Halides for New Material Discovery.

Recently, metal halide perovskites (MHPs) have emerged as a new class of materials for optical and electronic applications such as solar cells and ionizing radiation detectors. Although the solution-processability of MHPs is among their greatest advantages, the solution chemistries of most metal halide systems and their relationship with the observed structural and chemical diversity are poorly understood. In this work, we study the solution chemistry of a model indium halide system, methylammonium (MA)-In-Br, using a combination of the UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS) measurements, small-angle X-ray scattering (SAXS), and density functional theory (DFT) calculations. Our results show that indium could form either octahedral [InBr63-] or tetrahedral [InBr4-] anions in solution or a combination of both, depending on the loading ratios of MABr and InBr3 reactants. Understanding the solution chemistry of this system and recognizing the optical fingerprints of these polyanions allow for targeted crystallization of two novel compounds: MAInBr4 featuring tetrahedral [InBr4-] anions and MA2InBr5 containing both octahedral [InBr63-] and tetrahedral [InBr4-] anions. Further increase of the MABr content leads to the formation of previously reported MA4InBr7, containing only octahedral [InBr63-] anions separated by Br- anions. Our results suggest that understanding the solution chemistry of multinary metal halide systems could be a valuable tool for discovering functional materials for practical applications.

Zero-Dimensional Hybrid Organic-Inorganic Indium Bromide with Blue Emission.

Low-dimensional hybrid organic-inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic-inorganic halide, RInBr4, featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R+) cations and nonemissive InBr4- tetrahedral anions. The crystal structure of RInBr4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l'Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

(NH4)2AgX3 (X = Br, I): 1D Silver Halides with Broadband White Light Emission and Improved Stability.

Recently, ternary copper(I) halides have emerged as alternatives to lead halide perovskites for light emission applications. Despite their high-efficiency photoluminescence (PL) properties, most copper(I) halides are blue emitters with unusually poor tunability of their PL properties. Here, we report the impact of substitution of copper with silver in the high-efficiency blue-emitting Cu(I) halides through hydrothermal synthesis and characterization of (NH4)2AgX3 (X = Br, I). (NH4)2AgX3 are found to exhibit contrasting light emission properties compared to the blue-emitting Cu(I) analogues. Thus, (NH4)2AgBr3 and (NH4)2AgI3 exhibit broadband whitish light emission at room temperature with PL maxima at 394 and 534 nm and full width at half-maximum values of 142 and 114 nm, respectively. Based on our combined experimental and computational results, the broadband emission in (NH4)2AgX3 is attributed to the presence of high-stability self-trapped excitons and defect-bound excitons. (NH4)2AgBr3 and (NH4)2AgI3 both have significantly improved air and moisture stability as compared to the related copper(I) halides, which are prone to degradation via oxidation. Our results suggest that silver halides should be considered alongside their copper analogues for high-efficiency light emission applications.