Charge Transfer Phenomena Research Articles

Unraveling the Optimal Cerium Content for Boosting the Photoresponse Activity of Mixed-Metal Zr/Ce-Based Metal-Organic Frameworks through a Photodynamic and Photocurrent Correlation: Implications on Water Splitting Efficiency.

Mixed-metal-organic frameworks (MMOFs) have emerged as promising photocatalyst candidates in multiple reactions. For instance, the doping of Zr-UiO-type MOFs with Ce atoms increases their photoactivity owing to a better overlap between the organic linker and Ce orbitals. However, it is not clear which is the ideal content of Ce to reach the optimal photocatalytic performance. Herein, a series of MMOFs isostructural to UiO-66 and with napthalene-2,6-dicarboxylate (NDC) as a linker were synthesized and characterized. The Ce content was varied from 0 to 100% and their corresponding structural, chemical, photodynamic, and photoresponse properties were investigated. Powder X-ray diffraction shows that when the content of Ce is 12% onward, in addition to the UiO-type structure, a second crystalline structure is cosynthesized (NDC-Ce). Steady-state and femtosecond (fs) to millisecond (ms) spectroscopy studies reveal the existence of two competing processes: a linker excimer formation and an ultrafast ligand-to-cluster charge transfer (LCCT) phenomenon from the organic linker to Zr/Ce metal clusters. The ultrafast (fs-regime) LCCT process leads to the formation of long-lived charge-separated states, which are more efficiently photoproduced when the content of Ce reaches 9%, suggesting that the related material would show the highest photoactivity. Photoaction spectroscopic measurements corroborate that the sample with 9% of Ce exhibits the maximum photocatalytic efficiency, which is reflected in a 20% increment in overall water splitting efficiency compared with the monometallic Zr-based MOF. The current study demonstrates the relationship between the photodynamical properties of the MMOFs and their photocatalytic performance, providing new findings and opening new ways for improving the design of new MOFs with enhanced photocatalytic activities.

Photophysical Characterization of Ru Nanoclusters on Nanostructured TiO2 by Time-Resolved Photoluminescence Spectroscopy.

Despite the promising performance of Ru nanoparticles or nanoclusters on nanostructured TiO2 in photocatalytic and photothermal reactions, a mechanistic understanding of the photophysics is limited. The aim of this study is to uncover the nature of light-induced processes in Ru/TiO2 and the role of UV versus visible excitation by time-resolved photoluminescence (PL) spectroscopy. The PL at a 267 nm excitation is predominantly due to TiO2, with a minor contribution of the Ru nanoclusters. Relative to TiO2, the PL of Ru/TiO2 following a 267 nm excitation is significantly blue-shifted, and the bathochromic shift with time is smaller. We show by global analysis of the spectrotemporal PL behavior that for both TiO2 and Ru/TiO2 the bathochromic shift with time is likely caused by the diffusion of electrons from the TiO2 bulk toward the surface. During this directional motion, electrons may recombine (non)radiatively with relatively immobile hole polarons, causing the PL spectrum to red-shift with time following excitation. The blue-shifted PL spectra and smaller bathochromic shift with time for Ru/TiO2 relative to TiO2 indicate surface PL quenching, likely due to charge transfer from the TiO2 surface into the Ru nanoclusters. When deposited on SiO2 and excited at 532 nm, Ru shows a strong emission. The PL of Ru when deposited on TiO2 is completely quenched, demonstrating interfacial charge separation following photoexcitation of the Ru nanoclusters with a close to unity quantum yield. The nature of the charge-transfer phenomena is discussed, and the obtained insights indicate that Ru nanoclusters should be deposited on semiconducting supports to enable highly effective photo(thermal)catalysis.

Modelling TiO2 photoanodes for PEC water splitting: Decoupling the influence of intrinsic material properties and film thickness

Semiconductor metal oxides are intensively studied in electrodes for photoelectrochemical (PEC) water splitting. On a series of nanoparticulate TiO2 photoanodes, we analyze specific fabrication variables by means of data fitting. First, the experimental outcome is gathered using PEC characterization techniques, mostly cyclic voltammetry and transient photocurrent measurements. Subsequently, we apply models to gain insights into the involved charge trapping and transfer phenomena. We find that capacitance coefficients and the switch-on transient kinetics depend on the TiO2 layer thickness, respectively indicating surface mechanisms and stationary regimes that are mediated by light accessibility. On the contrary, exponential factors of capacitance are independent of thickness, but reflect changes in the density of electron states with different sintering atmospheres. Also, the transfer resistance in the electrolyte side is indirectly influenced by sintering. Through meticulous quantitative analysis of trends, we stablish simple mathematical relationships that connect thickness-dependent parameters. This knowledge delves into fundamental mechanisms governing the TiO2 photoelectrode behaviour, and aims to facilitate further improvements in the efficiency of materials and electrodes for green hydrogen production.

Ultrafast Electronic Coupling Estimators: Neural Networks versus Physics-Based Approaches.

Fast and accurate estimation of electronic coupling matrix elements between molecules is essential for the simulation of charge transfer phenomena in chemistry, materials science, and biology. Here we investigate neural-network-based coupling estimators combined with different protocols for sampling reference data (random, farthest point, and query by committee) and compare their performance to the physics-based analytic overlap method (AOM), introduced previously. We find that neural network approaches can give smaller errors than AOM, in particular smaller maximum errors, while they require an order of magnitude more reference data than AOM, typically one hundred to several hundred training points, down from several thousand required in previous ML works. A Δ-ML approach taking AOM as a baseline is found to give the best overall performance at a relatively small computational overhead of about a factor of 2. Highly flexible π-conjugated organic molecules like non-fullerene acceptors are found to be a particularly challenging case for ML because of the varying (de)localization of the frontier orbitals for different intramolecular geometries sampled along molecular dynamics trajectories. Here the local symmetry functions used in ML are insufficient, and long-range descriptors are expected to give improved performance.

Determination of the Electrical Parameters of Iodine-Doped Polymer Solar Cells at the Macro- and Nanoscale for Indoor Applications

In this work, macro- and nanodiagnostic procedures for working, third-generation photovoltaic devices based on a modified polymer:fullerene (P3HT:PCBM) absorber were conducted using atomic force microscopy (AFM) and impedance spectroscopy (IS) equipment. All experiments were performed both in the dark and under irradiation with a specific light wavelength. Photoactive Kelvin probe force microscopy (p-KPFM) and impedance spectroscopy (p-IS) experiments were conducted on half- and whole-solar cell devices. Based on the p-KPFM measurements, the surface potential (SP) and surface photovoltage (SPV) on top of the active layer at the micro/nanoscale were estimated for various light wavelengths (red, green, blue, and white). For light in the red spectrum range, which was associated with an optical absorption edge and acceptor states that occurred in the band gap of the P3HT material after doping the donor polymer with iodine, the SPV was measured at levels of 183 mV, 199 mV, and 187 mV for the samples with 0%, 5% and 10% iodine doping, respectively. In addition, a macroscale investigation enabling the determination of the electrical parameters of the studied organic solar cells (OSCs) was carried out using p-IS. Based on the data obtained during p-IS experiments, it was possible to propose a series electrical equivalent circuit to define and describe the charge transfer phenomenon in the OSCs. Estimations of data obtained from the fitting of the experimental results of p-IS under white light allowed us to evaluate the average diffusion time of electric charges at 8.15 µs, 16.66 µs, and 24.15 µs as a function of organic layer thickness for the device without doping and with 5% and 10% iodine doping. In this study, we demonstrated that correlating information obtained at the macro- and nanoscale enabled a better understanding of the electrical charge distribution of OSCs for indoor applications.

Solid-state emissive Zn2+ directed metallo-supramolecular polymers of bis-terpyridine appended aryl substituted buta-1,3-diene derivatives: Synthesis, photo-physical and electrochemical properties

Herein, two solid-state emissive monomers (TBBTP and ABTP) of bisterpyridine (bis-tpy) appended with twisted aryl substituted buta-1,3-diene central core have been designed and developed to investigate metal directed assembly to metallo-supramolecular homopolymers, TBBTP-Zn and ABTP-Zn and a copolymer, ATBBTP-Zn with zinc ion. The formation as well as purities of the monomers have been checked by NMR, FT-IR spectroscopy and mass spectrometry studies and the polymers have been characterised via NMR and FT-IR studies. Prior to optical studies, density functional theory (DFT) studies have been performed to rationalize the electronic distributions in HOMOs and LUMOs of monomers and their corresponding Zn complexes to unveil the phenomenon of intramolecular charge transfer. Absorption and emission studies performed in solution as well as in solid state have indicated that the monomers and its metallo-supramolecular polymers are emissive in solution as well as in solid state. However, the emission maxima at 608 nm, 576 nm and 590 nm of the metallo-supramolecular polymers, TBBTP-Zn, ABTP-Zn and ATBBTP-Zn respectively are clearly red shifted from monomers (466 nm for TBBTP and 490 nm for ABTP) and the fluorescence lifetime values measured by time-correlated single photon counting (TCSPC) are increased in solution as well as in solid state after coordination with Zn2+ ion owing to the charge-transfer processes from the central butadiene part to zinc coordinated terpyridine moiety. The HOMO and LUMO energies, band gaps of monomers (2.95 eV for TBBTP and 2.85 eV for ABTP) and polymers (2.73 eV, 2.84 eV and 2.73 eV for TBBTP-Zn, ABTP-Zn and ATBBTP-Zn respectively) have been estimated via electrochemical methods and it reveals that both monomers as well as polymers may be used in optoelectronic application.

Polarity and viscosity-sensitive fluorescence probes for lipid droplet imaging in cancer cells

Fluorescent probes sensitive to microenvironments have constantly been attractive, due to their significant benefits in monitoring changes in the pathophysiological microenvironment and their use in the early detection of associated disorders. In this work, we explored three new molecular rotors that could be potential candidates for detecting lipid droplets (LDs) in cancer cells based on coumarin derivatives connected with electron-donating polycyclic units including, tetraphenylethylene (LD-TPE), pyrene (LD-PYR), and 4,5-diphenylimidazole (LD-DIP). Gratifyingly, LD-PYR showed exceptional polarity and viscosity sensitivity and demonstrated bright fluorescence in highly viscous environments due to the suppression of the twisted intramolecular charge transfer (TICT) phenomenon and intramolecular rotation. Moreover, microenvironment-guided specific LD bioimaging by LD-PYR exhibited a reasonable ability to distinguish between cancer and noncancer cells. These data suggested that LD-PYR has interesting clinical diagnostic and microenvironment-related biological applications.

General Charge Transfer Dipole Model for AMOEBA-Like Force Fields.

The development of highly accurate force fields is always an importance aspect in molecular modeling. In this work, we introduce a general damping-based charge transfer dipole (D-CTD) model to describe the charge transfer energy and the corresponding charge flow for H, C, N, O, P, S, F, Cl, and Br elements in common bio-organic systems. Then, two effective schemes to evaluate the charge flow from the corresponding induced dipole moment between the interacting molecules were also proposed and discussed. The potential applicability of the D-CTD model in ion-containing systems was also demonstrated in a series of ion-water complexes including Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Zn2+, Pt2+, F-, Cl-, Br-, and I- ions. In general, the D-CTD model demonstrated good accuracy and good transferability in both charge transfer energy and the corresponding charge flow for a wide range of model systems. By distinguishing the intermolecular charge redistribution (charge transfer) under the influence of an external electric field from the accompanying intramolecular charge redistribution (polarization), the D-CTD model is theoretically consistent with current induced dipole-based polarizable dipole models and hence can be easily implemented and parameterized. Along with our previous work in charge penetration-corrected electrostatics, a bottom-up approach constructed water model was also proposed and demonstrated. The structure-maker and structure-breaker roles of cations and anions were also correctly reproduced using Na+, K+, Cl-, and I- ions in the new water model, respectively. This work demonstrates a cost-effective approach to describe the charge transfer phenomena. The water and ion models also show the feasibility of a modulated development approach for future force fields.

Enhanced efficiency of DSSCs by co-sensitizing dyes with complementary absorption spectra

In order to understand the mechanism of molecular improvement by dye co-sensitization at the microscale, a co-sensitized molecular system is simulated using density functional theory and time-dependent density functional theory. The single molecules AJ502 and TZ101 are first evaluated globally, with AJ502 having better spectral response performance and higher light absorption efficiency. The AJ502 molecule has a strong electron accept ability and intramolecular charge transfer phenomenon. These factors make the short circuit current density and photoelectric conversion efficiency of AJ502 have a very prominent performance. At the same time, the co-sensitization properties of AJ502 and TZ101 are investigated, finding that the overall molar extinction coefficient and charge transfer phenomenon of the co-sensitized system are enhanced. Most importantly, a detailed comparison of the effects of the two co-sensitized conformations on dye-sensitized solar cell devices shows that the H-H conformation is the most advantageous due to its more robust structure, pronounced red shift in the absorption spectrum and larger amount of intermolecular charge transfer.

Linear relationship between emission quantum yield and Stokes shift in 3-styryl aza-coumarin based dyes in the presence of cyclodextrins

The effect of the cyclodextrins inclusion on the Stokes shifts and emission quantum yield of three 3-styryl aza-coumarin dyes (SACs) was experimentally and theoretically studied. Preliminary results show a relationship between the emission quantum yield and the calculated binding constants. Supramolecular inclusion was supported by changes in the fluorescence spectra, high-resolution mass spectrometry and molecular dynamics studies. 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) presented higher binding constants than β-cyclodextrin (β-CD), along with up to a 6-fold increase in emission quantum yield for the SACs. Additionally, a linear negative correlation was obtained between the Stokes shift and the emission quantum yield. This linear and empirical relationship was explained by the action of a unique intramolecular rotation and charge transfer phenomenon in the dyes, which was modulated by cyclodextrins, and supported by calculations based on density functional theory.

Structural studies of a novel tautomeric Schiff base derived from 4-(N,N’-diethylamino)salicylaldehyde and 2-amino-4-methyl phenol: An experimental and theoretical study

A novel Schiff base, LMAP synthesized from 4-(N,N’-diethylamino)salicylaldehyde and 2-amino-4-methyl phenol has been characterized by single crystal X-ray diffraction and spectroscopic methods. DFT methods is used to investigate the enol-imine (EI) ⇄ keto-amine (KA) tautomeric behavior with respect to phase and in solvent media. The synthesized Schiff base crystallizes in the keto-amine (KA) form in the orthorhombic lattice and Pna21space group with four atoms per unit cell (Z = 4). Bond length analysis indicates that the KA form possesses significant zwitter ionic character. Study of electronic absorption and emission properties was conducted in the solid state as well as in different solvents. The UV–Vis result reveals the varied structural preference of the compound depending on the solvent media: polar protic solvents stabilize the KA form, while nonpolar and polar aprotic solvents favor the EI form. Quantum mechanical computations using DFT and TD-DFT also confirm these findings. Fluorescence emission spectra show multiple emission bands which indicate both excited state intramolecular proton transfer (ESIPT) and charge transfer (CT) phenomena occur simultaneously within the molecule. DFT predicted NLO responses of KA and EI were compared and found that the NLO response of KA is superior to that of EI.

Ultrafast Charge Transfer Mechanism in Van der Waals Heterostructures of Topological Insulators with 2D Materials

Hybridizing topological materials (TM) with two-dimensional (2D) materials has resulted in interesting structures, such as van der Waals heterostructures (vdW), having potential in optoelectronics. However, the performance of devices made out of such structures relies on the charge carrier interactions among the layers, which establishes the basic trade-off between the kinetically controlled charge carrier dynamics at the interface and the performance of vdW-based devices. In this perspective, three vdW are fabricated using a wet transfer technique, and the structures are probed to study the charge carrier and phonon dynamics among the TM (a few layered Bi2Te3) and 2D systems. The three different vdW fabricated in this article are graphene/Bi2Te3 (G/BT), fluorographene/Bi2Te3 (FG/BT), and monolayer MoS2/Bi2Te3 (MS/BT). Raman spectroscopy establishes the formation of all of these vdW and indicates the occurrence of the charge transfer (CT) phenomenon among them, which is further probed using ultrafast pump–probe spectroscopy. The charge carrier and phonon dynamics reveal the presence of the occurrence of the CT mechanism in all of the vdW. These spectra are further used to model the bands between different types of heterointerfaces, such as the Schottky junction between graphene and Bi2Te3 and the type II heterojunction between FG/BT and MS/BT. With the help of band alignment and charge carrier and phonon dynamics studies presented, a unique CT mechanism and excitonic peak tunability in vdW are proven, where such information is essential in developing highly sensitive optoelectronic and spintronic devices

First-principles rationalization of self-reduction and lanthanide defect levels in SrB4O7

The ``abnormal'' self-reduction of several trivalent lanthanides in borates has been reported for a couple of decades, especially in ${\mathrm{SrB}}_{4}{\mathrm{O}}_{7}$, but only a phenomenological explanation has been given. Our calculations of the formation energies of lanthanide-doped and intrinsic defects in ${\mathrm{SrB}}_{4}{\mathrm{O}}_{7}$ provide an explanation for the mechanisms of self-reduction phenomena. Furthermore, we also give the trends of the $4f$ and $5d$ host referred binding energies of divalent lanthanides, which well fits and supports the result based on the extrapolation of the experimental data with the semiempirical chemical shift model [P. Dorenbos, Phys. Rev. B 85, 165107 (2012)]. Our results show that the calculations based on the supercell method by employing the projector augmented wave pseudopotentials are capable of interpreting the reduction and charge-transfer phenomena, and can provide a basis for the design of lanthanide-doped optical materials.

Sensor Performance and Structural Characteristics of CrxFe3−xO4 Ferrofluids

The CrxFe[Formula: see text]O4 ferrofluids have been successfully synthesized using natural iron sand through co-precipitation method as a voltage sensor. The use of chromium dopants is intended to increase the ferrofluids response when used as a voltage sensor. A series of characterizations were carried out to support this justification, including structure, morphology, functional groups, optical properties, and sensor performance of the CrxFe[Formula: see text]O4 ferrofluids. The increase in the Cr[Formula: see text] molar fraction has an impact on decreasing in structural parameters of the CrxFe[Formula: see text]O4 ferrofluids. Visually, the particles show an agglomeration phase by the presence of interparticle forces. The study of functional groups showed that the CrxFe[Formula: see text]O4 ferrofluids had been successfully formed, marked by the appearance of all precursor functional groups. Analysis of optical properties based on absorption shows the phenomenon of intervalence charge transfer and causes a decrease in the value of the gap energy. Interestingly, the CrxFe[Formula: see text]O4 ferrofluids sensor sensitivity shows a good and prospective response making them suitable for new sensor candidates in the future.

Sustainable natural chlorogenic acid as a functional molecular sensor toward viscosity detection in liquids.

Liquids are perishable at ease during the long-term transportation and storage processes, non-invasive and in situ inspection method is urgent to be developed. In consideration of the important role of viscosity, one kind of sustainable natural product chlorogenic acid (CA) extracted from honeysuckle has been used as a versatile optical sensor for viscosity determination during the liquid spoilage process. The natural molecule was conducted by the O-diphenyl and carboxylic acid ester groups in coincidence, a typical twisted intramolecular charge transfer phenomenon was formed. This sensor features wide adaptability, high selectivity, good sensitivity, and excellent photo stability in various liquids. And CA displays a larger Stokes shift, high viscosity sensitive coefficient (0.62), and narrower energy band. The rotatable conjugate structure can be acted as the recognition site, and the bright fluorescent signal of CA is specifically activated when in the high viscous micro-environment. Inspired by this objective phenomenon, CA has been applied to detect the thickening efficiency of various food thickeners. More importantly, the viscosity fluctuations during the deterioration stage of liquids can be screened through non-invasive and in situ monitoring. We expected that more natural products can be developed as molecular tools for liquids safety investigation, and fluorescent analytical methods can be expanded toward interdisciplinary research.

Surface stabilisation of the high-spin state of Fe(II) spin-crossover complexes.

Temperature dependent X-ray photoemission spectroscopy (XPS) has been employed to examine the Fe 2p and N 1s core levels of the studied Fe(II) spin crossover (SCO) complexes of interest, namely: Fe(phen)2(NCS)2, [Fe(3-Fpy)2{Ni(CN)4}], and [Fe(3-Fpy)2{Pt(CN)4}]. The changes in the Fe 2p core-level spectra with temperature indicate spin state transitions in these SCO complexes, which are consistent with one's expectations and the existing literature. Additionally, the temperature dependence of the binding energy of the N 1s core-level provides further physical insights into the ligand-to-metal charge transfer phenomenon in these molecules. The high-spin fraction versus temperature plots reveal that the surface of each of the molecules studied herein is found to be in the high-spin state at temperatures both in the vicinity of room temperature and below their respective transition temperature alike, with the stability of the high-spin state of these molecules varying with the choice of ligand.

Exploitation of mixed-valency chemistry for designing a monolayer with double ferroelectricity and triferroic couplings.

Mixed-valence compounds possess both intriguing chemical and physical properties such as the intervalence charge transfer band and thus have been excellent model systems for the investigation of fundamental electron- and charge-transfer phenomena. Herein, we show that valence stratification can be a source of symmetry breaking and generating ferroelectricity in two-dimensional (2D) materials. We present ab initio computation evidence of the monolayer Cu2Cl3 structure with Cu ions being stratified into two separated layers of Cu(I) and Cu(II). Chemically, this unique monolayer not only entails lower formation energy than the bulk CuCl + CuCl2, but also enables the swapping of two valences through vertical ferroelectric switching, leading to a hitherto unreported chemical valencing phenomenon. Notably, the Jahn-Teller distortion of the Cu(II) layer results in another source of symmetry breaking and thus in-plane ferroelectricity. Apart from the valence swapping and self-contained double ferroelectricity, the monolayer's ferroelasticity is also coupled with in-plane ferroelectricity, while the monolayer's ferromagnetism is coupled with vertical polarization owing to the distinct magnetization of each Cu(I) and Cu(II) layer, thereby evoking the long-sought 2D triferroicity as well as triferroic couplings.

Pressure induced weakness of electrostatic interaction and solid decomposition in Cs-I compounds.

This work utilized first-principles calculations and the CALYPSO structure search technique to systematically investigate the crystal structure stability of CsxIy compounds under high pressures ranging from 0 to 500 GPa. Several new phases with both conventional and unconventional stoichiometries were predicted. Interestingly, we discovered a counter-intuitive phenomenon where Cs-I compounds decompose into Cs and I elemental solids under pressure. To understand the physical mechanism behind this pressure-induced decomposition, we examine the phenomenon from two distinct perspectives: enthalpy of formation and interatomic interactions. Our results suggest that the main cause is the weakening of electrostatic interactions leading to the decomposition, while the weak covalent interaction plays a minor role. From an energy perspective, the decrease in the formation of enthalpy (ΔH) is primarily due to a reduction in the difference of internal energy (ΔU). These findings provide valuable insights into the decomposition mechanism and high-pressure properties of alkali metal halides. The counterintuitive phenomenon of high-pressure charge transfer and decomposition may inspire new ideas and perspectives in the fields of geology and the study of alkali metal halides under extreme conditions.

Solvatochromic behaviour of cyclic dithioether-functionalized triphenylamine ligands and their mechano-responsive Cu(I) coordination polymers.

Cu(I)-based coordination polymers (CPs) are known as efficient emissive materials providing an eco-friendly and cost-effective platform for the development of various functional materials and sensors. In addition to the nature of the metal center, organic ligands also play a crucial role in controlling the emissive properties of coordination polymers. Herein, we report on the synthesis of dithiane- and dithiolane-substituted triphenylamine ligands L1 and L2. These ligands were found to be emissive both in the solid state and in solution. In addition, these ligands exhibit solvatochromic behaviour due to the twisted intramolecular charge transfer (TICT) phenomenon. Next, coordination behaviour of these ligands was explored with Cu(I)X salts (X = Br and Cl) and four new 1D coordination polymers [{Cu(μ2-X)2Cu}(μ2-L)]n, CP1 (X = Br, L = L1), CP2 (X = Cl, L = L1), CP3 (X = Br, L = L2), and CP4 (X = Cl, L = L2) were synthesized and crystallographically characterized. The emission behaviour of all the CPs suggests ligand-centered transitions. On mechanical grinding, emission maxima (λem) for CP1 and CP2 were blue-shifted, whereas for CP3 and CP4 red-shifts were observed. All CPs were found to emit at 448 nm with increased intensity after grinding. It is supposed that grinding is responsible for a change in the spatial arrangement (dihedral angles) of the phenyl groups of triphenylamine, causing the observed emission shifts. Furthermore, the higher emission intensity after grinding suggests the occurrence of a similar phenomenon as an aggregation-induced quenching in these CPs.

The phenomena of radiative association and charge transfer observed in Ar H and Ar H collisions

The aim of the present theoretical work is the characterization of argonium, namely, the molecular ions and , revealed in the last decade in the Crab Nebula and the PKS 1823-211 galaxy. The intent is to scrutinize the radiative processes of association, , and charge transfer, . To accomplish these two tasks, the corresponding potential-energy curves and dipole moments are chosen to construct the ground and the two first excited molecular states. Once all the required curves are well established and their physical and spectroscopic values are contrasted with previous published data, the cross sections, for the formation of the ionic dimer by radiative association and for the radiative charge transfer in the collisions, are computed quantum-mechanically at lower and higher energies. Finally, the temperature-dependent rate coefficients are calculated, and the numerical results are discussed and fitted to a selected analytical expression.