Low-Dimensional Organic Metal Halide Hybrids with Excitation-Dependent Optical Waveguides from Visible to Near-Infrared Emission

Integrating Full-Color 2D Optical Waveguide and Heterojunction Engineering in Halide Microsheets for Multichannel Photonic Logical Gates

Ensuring information security has emerged as a paramount concern in contemporary human society. Substantial advancements in this regard can be achieved by leveraging photonic signals as the primary information carriers, utilizing photonic logical gates capable of wavelength tunability across various time and spatial domains. However, the challenge remains in the rational design of materials possessing space-time-color multiple-resolution capabilities. In this work, a facile approach is proposed for crafting metal-organic halides (MOHs) that offer space-time-color resolution. These MOHs integrate time-resolved room temperature phosphorescence and color-resolved excitation wavelength dependencies with both space-resolved ex situ optical waveguides and in situ heterojunctions. Capitalizing on these multifaceted properties, MOHs-based two-dimensional (2D) optical waveguides and heterojunctions exhibit the ability to tune full-color emissions across the spectra from blue to red, operating within different spatial and temporal scales. Therefore, this work introduces an effective methodology for engineering space-time-color resolved MOH microstructures, holding significant promise for the development of high-density photonic logical devices.

Flexible Crystal Heterojunctions of Low-Dimensional Organic Metal Halides Enabling Color-Tunable Space-Resolved Optical Waveguides

Molecular luminescent materials with optical waveguide have wide application prospects in light-emitting diodes, sensors, and logic gates. However, the majority of traditional optical waveguide systems are based on brittle molecular crystals, which limited the fabrication, transportation, storage, and adaptation of flexible devices under diverse application situations. To date, the design and synthesis of photofunctional materials with high flexibility, novel optical waveguide, and multi-port color-tunable emission in the same solid-state system remain an open challenge. Here, we have constructed new types of zero-dimensional organic metal halides (Au-4-dimethylaminopyridine [DMAP] and In-DMAP) with a rarely high elasticity and rather low loss coefficients for optical waveguide. Theoretical calculations on the intermolecular interactions showed that the high elasticity of 2 molecular crystalline materials was original from their herringbone structure and slip plane. Based on one-dimensional flexible microrods of 2 crystals and the 2-dimensional microplate of the Mn-DMAP, heterojunctions with multi-color and space-resolved optical waveguides have been fabricated. The formation mechanism of heterojunctions is based on the surface selective growth on account of the low lattice mismatch ratio between contacting crystal planes. Therefore, this work describes the first attempt to the design of metal-halide-based crystal heterojunctions with high flexibility and optical waveguide, expanding the prospects of traditional luminescent materials for smart optical devices, such as logic gates and multiplexers.

High Emission Efficiency and Thermal Stability in Zero-Dimensional Hybrid Zinc Halide as a Blue Light Emitter

Exploring highly efficient blue-emissive lead-free halide materials is a significant and challenging objective in the study of luminescent materials. This study reports the synthesis of a new zero-dimensional (0D) hybrid zinc halide of [CYP]ZnBr4 (CYP = 1-cyclohexylpiperazine) containing an isolated [ZnBr4]2- tetrahedron. [CYP]ZnBr4 exhibits strong blue light emission with a high photoluminescence quantum yield (PLQY) of 79.22%, surpassing all previously reported 0D zinc halide counterparts. According to the theoretical and experimental studies, the blue light emission is attributed to intrinsic self-trapped excitons resulting from strong electron-phonon coupling and structural deformation. Importantly, [CYP]ZnBr4 demonstrates excellent structural and luminescence stability toward high temperatures (180 °C) over at least half a month. High luminescence efficiency and stability enable [CYP]ZnBr4 to be an efficient blue phosphor to fabricate white light-emitting diodes (LEDs), which produces high-quality white light with a color rendering index (CRI) of 93.1 and a correlated color temperature (CCT) of 5304 K, closely resembling natural sunlight. This white LED also exhibits consistent performance and stability across different drive currents, suggesting the potential for high-power optoelectronic applications. Overall, this study paves the way for the utilization of 0D hybrid halides in advanced solid-state lighting applications.

All-in-One Optoelectronic Logic Gates Enabled by Bipolar Spectral Photoresponse of CdTe/SnSe Heterojunction

Optoelectronic logic gate devices (OLGDs) have attracted significant attention in high-density information processors; however, multifunctional logic operation in a single device is technically challenging due to the unidirectional electrical transport. In this work, we deliberately design all-in-one OLGDs based on self-powered CdTe/SnSe heterojunction photodetectors. The SnSe nanorod (NR) array is grown on the sputtered CdTe film via a glancing-angle deposition technique to form a heterojunction device. At the interface, the photovoltaic (PV) effect in the CdTe/SnSe heterojunction and the photothermoelectric (PTE) effect from the SnSe NRs are combined together to induce the reversed photocurrent, leading to a unique bipolar spectral response. The competition between PV and PTE in different spectral ranges is thus employed to control the photocurrent polarity, and five basic logic gates of OR, AND, NAND, NOR, and NOT can be performed just with a single heterojunction. Our findings indicate the large potentials of the CdTe/SnSe heterojunctions as logic units in next-generation sensing-computing systems.

One-Dimensional Organic-Inorganic Lead Bromide Hybrids with Excitation-Dependent White-Light Emission Templated by Pyridinium Derivatives

Organic-inorganic hybrid metal halides have attracted widespread attention due to their excellent tunability and versatility. Here, we have selected pyridinium derivatives with different substituent groups or substitution positions as the organic templating cations and obtained six 1D chain-like structures. They are divided into three types: type I (single chain), type II (double chain), and type III (triple chain), with tunable optical band gaps and emission properties. Among them, only (2,4-LD)PbBr₃ (2,4-LD = 2,4-lutidine) shows an exciton-dependent emission phenomenon, ranging from strong yellow-white to weak red-white light. By comparing its photoluminescence spectrum with that of its bromate (2,4-LD)Br, it is found that the strong yellow-white emission at 534 nm mainly came from the organic component. Furthermore, through a comparison of the fluorescence spectra and lifetimes of (2,4-LD)PbBr₃ and (2-MP)PbBr₃ (2-MP = 2-methylpyridine) with similar structures at different temperatures, we confirm that the tunable emission of (2,4-LD)PbBr₃ comes from different photoluminescent sources corresponding to organic cations and self-trapped excitons. Density functional theory calculations further reveal that (2,4-LD)PbBr₃ has a stronger interaction between organic and inorganic components compared to (2-MP)PbBr₃. This work highlights the importance of organic templating cations in hybrid metal halides and the new functionalities associated with them.

Blue-Emitting Zero-Dimensional Inorganic-Organic Hybrids Constructed from Beta-Diketonate Ligands and Bulky Organic Cations

Two zero-dimensional inorganic-organic hybrids, namely, [C₄mim][Cd(TCDPPA)₃] (1) and [C₄mpy][Cd(TCDPPA)₃] (2), where (TCDPPA)^- = 2,2,2-trichloro-N-(di(pyrrolidin-1-yl)phosphoryl)acetamide, (C₄mim)⁺ = 1-butyl-3-methylimidazolium, and (C₄mpy)⁺ = 1-butyl-4-methylpyridinium, have been synthesized via metathesis reactions and characterized systematically. These ionic cadmium-containing inorganic-organic hybrid compounds are assembled from a bulky organic cation and a complex anion constructed from the chelation of three TCDPPA ligands to one cadmium ion. These compounds possess wide band gaps and emit in the deep-blue region intensely with a quantum yield as high as 34.04%. The success of this work provides a new method for the design and fabrication of high-efficiency blue-emitting materials.

Organic Cation-Directed Modulation of Emissions in Zero-Dimensional Hybrid Tin Bromides

Zero-dimensional hybrid metal halides (0D HMHs) are attractive due to their intriguing self-trapped exciton (STE) emission properties. However, the effect of organic cations on the emission of 0D HMHs is relatively underexplored. Herein, we report two types of 0D hybrid tin bromides, (BMe)₂SnBr₆ (BMe = C₈N₂H₁₈) and (MeH)₂SnBr₆ (MeH = C₇N₂H₁₆), which share similar structural features with different hydrogen bonding (HB) interactions between [SnBr₆]^4- anions and organic cations. The (BMe)₂SnBr₆ with weak HB interactions exhibits only STE emission, while the (MeH)₂SnBr₆ exhibits both STE and charge transfer exciton emissions owing to the strong HB interactions, resulting in an excitation-dependent emission at cryogenic conditions. Detailed structural analyses and Hirshfeld surface calculations confirm that the enhanced HB interactions are essential to obtain the multiple emissions in (MeH)₂SnBr₆.

Excitation-Dependent Luminescence of 0D ((CH3)4N)2ZrCl6 across the Full Visible Region

Herein, we report a novel hybrid organic-inorganic Zr(IV) metal halide ((CH₃)₄N)₂ZrCl₆, which demonstrates fascinating excitation-dependent luminescence across the full visible region. The single crystal of ((CH₃)₄N)₂ZrCl₆ showed an unexpected high degree of symmetry and formed a unique 0D structure with isolated [ZrCl₆]^2- octahedrons. Amazingly, three different emission groups emerged under changeable excitation light. The first emission group peaked at 462 nm with a ns lifetime and a μs lifetime, which is assigned to free-exciton fluorescence and thermally activated delayed fluorescence (TADF). The second group of emissions featured elaborate multipeak light-emitting components, which is ascribed to the d-d transitions of Zr(IV). The third emission group centered at 660 nm was attributed to the typical self-trapped exciton (STE) emission. To our best knowledge, this work for the first time reports a 0D organic-inorganic metal halide with distinctive excitation-dependent full-visible-spectrum luminescence via four different emission mechanisms.

A Long Short-Term Memory Neural Network Based Simultaneous Quantitative Analysis of Multiple Tobacco Chemical Components by Near-Infrared Hyperspectroscopy Images

Near-infrared (NIR) spectroscopy has been widely used in agricultural operations to obtain various crop parameters, such as water content, sugar content, and different indicators of ripeness, as well as other potential information concerning crops that cannot be directly obtained by human observation. The chemical compositions of tobacco play an important role in the quality of cigarettes. The NIR spectroscopy-based chemical composition analysis has recently become one of the most effective methods in tobacco quality analysis. Existing NIR spectroscopy-related solutions either have relatively low analysis accuracy, or are only able to analyze one or two chemical components. Thus, a precise prediction model is needed to improve the analysis accuracy of NIR data. This paper proposes a tobacco chemical component analysis method based on a neural network (TCCANN) to quantitatively analyze the chemical components of tobacco leaves by using NIR spectroscopy, including nicotine, total sugar, reducing sugar, total nitrogen, potassium, chlorine, and pH value. The proposed TCCANN consists of both residual network (ResNet) and long short-term memory (LSTM) neural network. ResNet is applied to the feature extraction of high-dimension NIR spectroscopy, which can effectively avoid the gradient-disappearance issue caused by the increase of network depth. LSTM is used to quantitatively analyze the multiple chemical compositions of tobacco leaves in a simultaneous manner. LSTM selectively allows information to pass through by a gated unit, thereby comprehensively analyzing the correlation between multiple chemical components and corresponding spectroscopy. The experimental results confirm that the proposed TCCANN not only predicts the corresponding values of seven chemical components simultaneously, but also achieves better prediction performance than other existing machine learning methods.