Alkali Metal Ions Research Articles

Structural Characterization of the Metalized Radical Cations of Adenosine ([Ade+Li-H]•+ and [Ade+Na-H]•+) by Infrared Multiphoton Dissociation Spectroscopy and Theoretical Studies.

Nucleoside radicals are key intermediates in the process of DNA damage, and alkali metal ions are a common group of ions in living organisms. However, so far, there has been a significant lack of research on the structural effects of alkali metal ions on nucleoside free radicals. In this study, we report a new method for generating metalized nucleoside radical cations in the gas phase. The radical cations [Ade+M-H]•+ (M = Li, Na) are generated by the 280 nm ultraviolet photodissociation (UVPD) of the precursor ions of lithiated and sodiated ions of 2-iodoadenine in a Fourier transform ion cyclotron resonance (FT ICR) cell. Further infrared multiphoton dissociation (IRMPD) spectra of both radical cations were recorded in the region of 2750-3750 cm-1. By combining these results with theoretical calculations, the most stable isomers of both radicals can be identified, which share the common characteristics of triple coordination patterns of the metal ions. For both radical species, the lowest-energy isomers undergo hydrogen transfer. Although the sugar ring in the most stable isomer of [Ade+Li-H]•+ is in a (South, syn) conformation similar to that of [Ado+Na]+, [Ade+Na-H]•+ is distinguished by the unexpected opening of the sugar ring. Their theoretical spectra are in good agreement with experimental spectra. However, due to the flexibility of the structures and the complexity of their potential energy surfaces, the hydrogen transfer pathways still need to be further studied. Considering that the free radicals formed directly after C-I cleavage have some similar spectral characteristics, the existence of these corresponding isomers cannot be ruled out. The findings imply that the structures of nucleoside radicals may be significantly influenced by the attached alkali metal ions. More detailed experiments and theoretical calculations are still crucial.

Unveiling of a puzzling dual ionic migration in lead‐ and iodide‐deficient halide perovskites (d‐HPs) and its impact on solar cell J–V curve hysteresis

AbstractHalide perovskite solar cells are characterized by a hysteresis between current–voltage (J–V) curves recorded on the reverse and on the forward scan directions, and the suppression of this phenomenon has focused great attention. In the present work, it is shown that a special family of 3D perovskites, that are rendered lead ‐and iodide‐ deficient (d‐HPs) by incorporating large organic cations, are characterized by a large hysteresis. The strategy of passivating defects by K+, which has been successful in reducing the hysteresis of 3D perovskite perovskite solar cells, is inefficient with the d‐HPs. By glow discharge optical emission spectroscopy (GD‐OES), the existence of the classic iodide migration in these layers is unveiled, which is efficiently blocked by potassium cation insertion. However, it is also shown that it co‐exists with the migration of the large organic cations characteristics of d‐HPs which are not blocked by the alkali metal ion. The migration of those large cations is intrinsically linked to the special structure of the d‐HP. It is suggested that it takes place through channels, present throughout the whole perovskite layer after the substitution of PbI+ units by the large cations, making this phenomenon intrinsic to the original structure of d‐HPs.

Novel phenolate salts of bioactive agents: Cannabidiol phenolate salts

Bioactive phenolic compounds are commonly found in medications, with examples including apomorphine, estrone, thymol, estradiol, propofol, o-phenylphenol, l-Dopa, doxorubicin, tetrahydrocannabinol (THC), and cannabidiol (CBD). This study is the first to explore the creation and assessment of metal and ammonium phenolate salts using CBD as an example. CBD is used in medicine to treat anxiety, insomnia, chronic pain, and inflammation, but its bioavailability is limited due to poor water solubility. In this study exploit a synthetic route to convert CBD into anionic CBD-salts to enhance water solubility. Various CBD-salts with metal and ammonium counterions such as lithium (Li+), sodium (Na+), potassium (K+), choline hydroxide ([(CH3)3NCH2CH2OH]+), and tetrabutylammonium ([N(C4H9)4]+) have been synthesized and characterized. These salts are obtained in high yields, ranging from 74 % to 88 %, through a straightforward dehydration reaction between CBD and alkali metal hydroxides (LiOH, NaOH, KOH) or ammonium hydroxides (choline hydroxide, tetrabutylammonium hydroxide). These reactions are conducted in either ethanol, methanol, or a methanol:water mixture, maintaining a 1:1 molar ratio between the reactants. Comprehensive characterization using Fourier-Transform Infrared Spectroscopy (FT-IR), Nuclear Magnetic Resonance (NMR) spectroscopy, and elemental (CHN) analysis confirms the formation of CBD-salts, as evidenced by the absence of aromatic hydroxyl resonances or stretching frequencies. The molecular formulas of CBD salts were determined based on CHN analysis, and CBD quantification from acid regeneration experiments. Characterization data confirms that each CBD phenolate in a specific CBD salt was electrostatically stabilized by one of the either alkali metal or ammonium ion. The CBD-salts are highly susceptible to acidic conditions, readily reverting back to the original CBD. The percentage and purity of CBD in the CBD-metal/ammonium salts have been studied using High-Performance Liquid Chromatography (HPLC) analysis. Solubility studies indicate that the conversion of CBD into CBD salts significantly enhances its solubility in water, ranging from 110 to 1606 folds greater than pure CBD. Furthermore, the pharmacokinetic evaluation of oral administration of CBD-salts compared to CBD were determined in rats.

Ecofriendly alkali metal cations diffusion improves fabrication of mixed-phase titania polymorphs on fixed substrate by chemical vapor deposition (CVD) for photocatalytic degradation of azo dye

Controlling the nanoscale synthesis of semiconductor TiO2 on a fixed substrate has fascinated the curiosity of academics for decades. Synthesis development is required to give an easy-to-control technique and parameters for TiO2 manufacture, leading to advancements in prospective applications such as photocatalysts. This study, mixed-phase TiO2(B)/other titania thin films were synthesized on a fused quartz substrate utilizing a modified Chemical vapor depodition involving alkali-metal ions (Li+, Na+, and K+) solution pre-treatment. It was discovered that different cations promote dramatically varied phases and compositions of thin films. The films had a columnar structure with agglomerated irregular-shaped particles with a mean thickness of 800–2000 nm. Na+ ions can promote TiO2(B) more effectively than K+ ions, however Li+ ions cannot synthesize TiO2(B). The amounts of TiO2(B) in thin films increase with increasing alkali metal (K+ and Na+) concentration. According to experimental and DFT calculations, the hypothesized TiO2(B) production mechanism happened via the meta-stable intermediate alkaline titanate transformation caused by alkali-metal ion diffusion. The mixed phase of TiO2(B) and anatase TiO2 on the fixed substrate (1 × 1 cm2) obtained from Na+ pre-treated procedures showed significant photocatalytic activity for the degradation of methylene blue. K2Ti6O12, Li2TiO3, Rutile TiO2, and Brookite TiO2 phase formations produced by K+ and Li + pretreatment are low activity photocatalysts. Photocatalytic activities were more prevalent in NaOH pre-treated samples (59.1% dye degradation) than in LiOH and KOH pre-treated samples (49.6% and 34.2%, respectively). This revealed that our developed CVD might generate good photocatalytic thin films of mixed-phase TiO2(B)/anatase TiO2 on any substrate, accelerating progress in future applications.

Subnanocyclic Molecule of 15-Crown-5 Inhibiting Interfacial Water Decomposition and Stabilizing Zinc Anodes via Regulation of Zn2+ Solvation Shell.

Aqueous zinc ion batteries exhibit a promising application prospect for next-generation energy storage devices. However, the decomposition of active H2O molecules on the Zn anode induces drastic dendrite formation, thereby impairing the performance for entire devices. To solve this challenge, we introduce subnanocyclic molecules of 15-Crown-5 as an additive into ZnSO4 electrolyte to stabilize the Zn anode. Owing to the binding property of crown ethers with alkali metal ions and the size-fit rule, the 15-Crown-5 additives enable effective regulation of the solvation structure of hydrated Zn2+ and reduce the efficient contact between Zn anode and active H2O, which are validated by the experimental analysis and theoretical calculations. Under the assistance of the 15-Crown-5 additive, the as-assembled Zn-based batteries deliver superior performance compared with ZnSO4 and 18-Crown-6contaning ZnSO4 electrolytes. This work shows a bright direction toward progress in aqueous batteries.

Location of Carbonate Ions in Metal-Doped Carbonated Hydroxylapatites

The environment model for the description of the location of carbonate ions in apatites predicts that approximately half of the carbonate occupies the apatite channel. This model relies on the influence of entities surrounding the carbonate on its IR spectrum and can be used to determine how various substituents affect the location and structure of that ion. Careful deconvolution (peak-fitting) of the asymmetric carbonate IR region was used to determine the percentage of A-type (channel) ions, A′-type (channel with either a Ca2+ vacancy or substitution of Na+ for Ca2+) ions, and B-type (substitution for phosphate) ions. In our previous applications of this model, we have looked at the effect of alkali metal ions, such as sodium, lithium, and potassium, the ammonium ion, and the rare earth europium ion. In the present work, we explore the incorporation of the first-row transition metal ions and find that they have little effect on the location of the carbonate ion. Like the un-substituted carbonated apatite, these apatites contain about half of the carbonate in the channel, at least in derivatives that contain up to half a mole of the metal ion per mole of apatite. Attempts to incorporate greater amounts of metal ions by aqueous ion-combination reactions generally lead to lower-resolution XRD patterns and IR spectra that produce greater uncertainties in the peak-fitting modeling.

Rare Earth Nitrate Hybrid Double Perovskites [Me4N]2[MLn(NO3)6] (M = Na-Cs; Ln = La-Gd, ex. Pm).

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A2B'BX6 (A = organocation, B' = M+, B = M3+, X = molecular bridging anion) that include X = NO3- and B' = alkali metal is reported, complementing earlier studies of the [Me4N]2[KB(NO3)6] (B = Am, Cm, La-Nd, Sm-Lu, Y) (Me4N = (CH3)4N+) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B'-site. Herein, we report three new series of the form [Me4N]2[B'B(NO3)6] (B = La-Nd, Sm-Gd; B' = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R3̅ to the high-symmetry, cubic space group Fm3̅m. The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm3̅m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

ZnS/SnS2 Heterostructures Encapsulated in N-Doped Carbon Nanofibers for High-Performance Alkali Metal-Ion Batteries.

Heterogeneous composite ZnS/SnS2 is designed to meet various requirements for alkali metal-ion batteries. The composite is prepared using an electrostatic spinning method and encapsulated in N-doped carbon fibers after high-temperature vulcanization. The special structure of the composite provides a dependable interconnection and fast conductive network for alkali metal ions. The conductive carbon network shortens the diffusion path and greatly improves the migration efficiency of the alkali metal ions in the electrode. As expected, when the current density is 0.1 A g-1, the ZnS/SnS2@NCNFs maintain a high discharge capacity of more than 1437.5, 1321.2, and 861.6 mA h g-1 for lithium-ion, sodium-ion, and potassium-ion batteries, respectively. What is more, a full cell using a prelithiated composite anode and a LiFePO4 cathode is tested and shows excellent electrochemical performance. This work provides new perspectives for the development of novel anodes that can efficiently store alkali metal ions, as well as for the fine-structure design of materials.

Photocatalytic degradation of alkyl imidazole ionic liquids by TiO2 nanospheres under simulated solar irradiation: Transformation behavior, DFT calculations and promoting effects of alkali and alkaline earth metal ions

In this study, TiO2 nanospheres prepared by the sol-gel method were found to efficiently catalyze the photodegradation of 1-butyl-2,3-dimethylimidazolium bromide salt ([BMMIm]Br) under simulated solar irradiation through the main attack of hydroxyl radicals (•OH). The promoting effect of alkali metal (Li+→Cs+) and alkaline earth metal ions (Mg2+→Ba2+) was particularly emphasized. In-situ EPR tests showed that the introduction of alkali and alkaline earth metal ions could enhance the formation of •OH thus leading to a 7%−30.3% increase in the degradation efficiency of. [BMMIm]+. Moreover, the removal efficiency of [BMMIm]+ still reached > 96.19% in four real waters. A total of 23 products of [BMMIm]Br were detected, and hydroxyl substitution, bond breaking, direct oxidation and ring opening were considered as the main reactions during the photocatalytic degradation process. The results of toxicity evaluation showed that hydroxylation was a reaction process of increasing toxicity, while the bond breaking reaction had great detoxification capacity for [BMMIm]+. These findings may enhance our understanding on the effects of alkali or alkaline earth metal ions on the photocatalytic activity of TiO2, which could also provide reference for the efficient and green removal of alkylimidazolium ionic liquids in waters.

Alkali metal ion-mediated ice nucleation

Understanding the effects of ion specificities on ice nucleation is essential for atmospheric science and biology. Although valence and concentration changes of ions can regulate ice nucleation, it is unclear if alkali metal ions of different species with the same valence can regulate ice nucleation. This study investigated the behavior of ice nucleation on alkali metal ion-modified surfaces with atomic-scale roughness and (sub)nanometer thickness to decouple the effect of alkali metal ions on ice nucleation. The results showed that modulating the type of alkali metal ion could regulate ice nucleation. Additionally, it was found that different hydration shells of alkali metal ions may influence the structure of interfacial water and the thermodynamic phase transition to play a key role in regulating ice nucleation. This study shed light on a long-standing problem of the mechanism of alkali metal ions in ice nucleation and provided a strategy for effectively regulating ice nucleation .

Influence of alkali metal ions (Li+, Na+, and K+) on the redox thermodynamics and kinetics of organic electrode materials for rechargeable batteries

Organic electrode materials have been widely applied in rechargeable Li, Na, and K batteries. However, one of the key scientific issues—the influence of Li+, Na+, and K+ ions on the redox thermodynamics and kinetics is still unclear. Herein, by using n-type poly(anthraquinonyl sulfide) (PAQS) and polyimide (PI) and p-type polytriphenylamine (PTPAn) as examples, we have systematically and deeply studied this problem though elaborate electrochemical tests and theoretical calculations. By employing three-electrode cells, the thermodynamic potentials of Li, Na, K metal electrodes as well as the PAQS, PI, and PTPAn organic electrodes have been accurately measured. They follow the order of Li+ > Na+ > K+ for PAQS and PI, and keep unchanged for PTPAn. As an application of this discovery, PAQS–PTPAn dual-ion full-cells show the highest output voltage and low-temperature performance with K+ ion. To explain the tendency, universal thermodynamic models have been established and the theoretical calculations reveal that with the increase of ionic radius, the interactions of metal ion with electrolyte solvent and discharged n-type organic (N–) become weaker, which lower down the thermodynamic potential and enhance the redox kinetics. This work provides a significant guidance for the design of high-performance organic batteries.

On the Influence of Counter-Ion Nature on Properties of Perfluorosulfonic Acid Membranes with Long and Short Side Chain

In this work, the study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in H+, Li+, Na+, and K+ forms and solutions of inorganic electrolytes is presented. The properties of the commercial Aquivion E87-05S and Nafion 212 membranes, as well as the membranes prepared from the dispersions of Nafion 212 in the solvents of different nature (N,N-dimethylformamide, 1‑methyl-2-pyrrolidone, isopropyl alcohol–water mixtures in volume ratio of 80–20) were investigated. The influence of the number of functional groups, the length of the side chains of the polymer macromolecules, and the polymer morphology in the membranes on their equilibrium and transport properties depending on the counter-ion nature was revealed. The effect of the relaxation and electrophoretic factors on the alkali metal ion transfer through the system of pores and channels of the perfluorosulfonic acid membranes was discussed. The slope of the concentration dependencies of the Donnan potential for all highly hydrated membranes in the H+ form was close to the Nernstian one, while the selectivity to the alkali metal ions increased for the membranes with the highest ion-exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of the co-ions from the membrane phase.

Bioderived Ionic Liquids with Alkaline Metal Ions for Transient Ionics (Small 36/2023)

Bioderived Ionic Liquids with Alkaline Metal Ions for Transient Ionics (Small 36/2023)

Luminescence and temperature-sensing properties of Li+, Na+, or K+, Tm3+, and Yb3+ co-doped Bi2WO6 phosphors

Abstract A series of Li+, Na+, or K+, Tm3+, and Yb3+ co-doped Bi2WO6 upconversion phosphors were prepared by a high-temperature solid-phase method at 800°C for 3 h. X-ray diffraction showed that Li+, Na+, K+, Tm3+, and Yb3+ doping did not affect the orthorhombic structure of the Bi2WO6 matrix. Scanning electron microscopy images of the Bi2WO6:1% Tm3+, 6% Yb3+ and 1% Li+, 1% Na+, or 1% K+-doped Bi2WO6:1% Tm3+, 6% Yb3+ samples reveal irregular particles with a 0.5–5 µm particle size range; upon Na+ or K+ doping, the particle size increases and the particle surface becomes smooth. EDS analysis shows that the above ions are well incorporated into the powder particles. At 298 K, the relative temperature sensitivities are 0.00144, 0.0016, 0.0024, and 0.0018 K−1 for the 1% Tm3+, 6% Yb3+:Bi2WO6 samples without alkali metal ions and doped with 1% Li+, 1% Na+, or 1% K+ based on the thermally coupled energy level 3F3/3F2 characterization temperature. However, under the same conditions, when using the nonthermally coupled level 3F3/1G4 characterization temperature, the relative temperature sensitivities of these four samples are 0.0378, 0.0166, 0.046, and 0.0257 K−1, increasing by 26.3, 10.3, 19.1, and 13.9 times, respectively. The relative temperature sensitivities of the 1% Na+, 1% Tm3+, and 6% Yb3+:Bi2WO6 samples are the highest at 298 K.

Modification of Misfit-Layered Cathode Materials for Improving Electrocatalyic Activity in Reversible Protonic Ceramic Cells

The demand for sustainable regeneration energies such as solar and wind has been continuously increasing by the rise of environmental issues. However, several major technical issues such as intermittent electricity production and high system construction cost are major obstacles to large-scale commercialization for regeneration energies [1]. Reversible protonic ceramic cells (RPCCs) can be an alternative choice because of their high efficiency, long-term durability at intermediate temperatures, and bifunctionality for producing both hydrogen and electricity in an electrochemical device [2]. Until now, perovskite-structured cathode (air/steam electrode) materials have been in spotlight due to their fast oxygen reaction kinetics in RPCCs [3]. However, in spite of their high electrocatalytic activity for oxygen electrode reactions (oxygen evolution and reduction), low phase stability in humid atmospheres, thermal expansion mismatch to common proton electrolytes, and relatively low proton conductivity of RPCCs are still major obstacles to enter the era of hydrogen economy [4, 5]. Hence, we demonstrate novel misfit-layered structure Ca3Co4O9+δ (CCO)-based materials to overcome these technical issues with superior catalytic activity for high performance RPCCs. The thermal expansion coefficient value of CCO is 10-12×10−6 K−1, which is relatively similar to that of the BaCeO3-based proton electrolytes, implying that the CCO-based materials are thermo-mechanically stable during cell operations [6]. In addition, the needle-like morphology of the CCO-based materials is quite valuable in the supply of steam (or air) to the catalytic active sites and elimination the water produced by the electrochemical reaction. Furthermore, with the doping of alkali metal ion (Li, Na, and K) into Ca-site, CCO generates extra charge carrier species with the modified Co oxidation state. This triggers the proton uptake and diffusion properties of CCO-based materials with the improved electrical conductivity. As a result, 5 mol% Na-doped CCO-cell shows exceptionally high performance in both protonic ceramic fuel cell and electrolysis cell modes for RPCCs.

Unexpected Potential Dependent HER Behaviors of Cationic Phosphorus Doped WO3 Nanosheets

TMOs are generally considered as catalytically inert for hydrogen evolution reaction (HER).[1] This unique property has promoted a wide variety of applications of TMOs, such as aqueous-based lithium ionic batteries, electrochromic smart windows, electrocatalysts and/or catalyst supports. However, hydrogen evolution as an undesired side reaction is commonly observed when they are used in aqueous-based supercapacitors and battery applications.[2] The unexpected HER mechanism for intrinsic TMOs has not been studied until very recently by McKone and Mpourmpakis groups.[3] With careful theoretical calculations, they clearly demonstrated that intrinsic WO3 is not HER active. Bulk hydrogen (H) intercalation into WO3 is a prerequisite for its catalytic activity toward HER. Applying electrochemical potential to WO3 primarily sets the bulk H stoichiometry of thus formed hydrogen bronzes HxWO3. The level of intercalation (x), precisely to say, the density of the intercalated hydrogen in the WO3, in turn determines the formation of W-H*, the bonding strength of W-H*, and their consumption to H2 (HER). Significant HER is only seen at potentials negative enough when x > 0.5. Beyond this intercalation level, HER is no longer dictated by potential-dependent activation energies, instead, is controlled by the density of the hydrogen intercalation on the surface of WO3 catalysts. In line with this extensive theoretical study, Augustyn group very recently experimentally demonstrated the dependence of HER activity of WO3 materials on their electrochemical insertion characteristics.[4] By including crystal water between the WO3 sheets, proton intercalation is greatly facilitated likely with a Grotthuss mechanism. Accordingly, the HER kinetics is largely improved with a large positive shift of the HER on-set potential. On the other hand, by inclusion of molecular pillars in the WO3 lattice to physically block proton intercalation, the HER activity of WO3 was largely inhibited. Recently, we developed a facile approach to cationically dope WO3 nanosheets with red phosphorus. The proton interaction and the associated HER behavior as a function of electrochemical potentials were carefully studied with multiple electrochemical techniques. Interestingly, we found that proton interaction is largely suppressed even without including molecular pillars in the P-doped WO3 lattice. At lower intercalation levels before the so-called “potential independent regime”, the HER kinetics is largely decreased, as expected, compared to the non-doped WO3 control sample. While in the “potential independent regime”, the HER kinetics is largely enhanced. Furthermore, including alkaline metal ions into the electrolyte, the HER kinetics is further suppressed as demonstrated by largely negatively shifted onset potentials and the increased Tafel slopes. Interestingly, in the “potential independent regime”, the HER kinetics is further drastically enhanced. Extensive structural characterization and theoretical calculations are undergoing to reveal the mechanism behind these interesting tunable potential dependent - proton interaction and HER behavior, which will be reported in this work. Understanding how heteroatomic doping could modulate proton interaction and HER behaviors of TMOs at atomic levels would provide practical guidance for designing more efficient and selective electrochemical catalysts for various catalytic reduction reactions, such as carbon dioxide reductions and nitrogen/nitrate reductions to valuable compounds.[1] Zhang, S.; Zhang, X.; Rui, Y.; Wang, R.; Li, X., Recent advances in non-precious metal electrocatalysts for pH-universal hydrogen evolution reaction. Green Energy & Environment 2021, 6 (4), 458-478.[2] Wang, R.; Mitchell, J. B.; Gao, Q.; Tsai, W.-Y.; Boyd, S.; Pharr, M.; Balke, N.; Augustyn, V., Operando Atomic Force Microscopy Reveals Mechanics of Structural Water Driven Battery-to-Pseudocapacitor Transition. ACS Nano 2018, 12 (6), 6032-6039.[3] Miu, E. V.; McKone, J. R.; Mpourmpakis, G., The Sensitivity of Metal Oxide Electrocatalysis to Bulk Hydrogen Intercalation: Hydrogen Evolution on Tungsten Oxide. Journal of the American Chemical Society 2022, 144 (14), 6420-6433.[4] Spencer, M. A.; Fortunato, J.; Augustyn, V., Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides. The Journal of Chemical Physics 2022, 156 (6), 064704. Figure 1

Novel Mn4+-activated fluoride red phosphors induced by alkaline metal ions replacement: Green synthesis, luminescence enhancement, high stability and application in warm WLED

Red-emitting Mn4+-doped fluoride phosphors are promising fluorescent material for use in high-performance warm white light emitting diodes (WLEDs). However, low stability and non-green synthesis method limit the development and commercialization of such phosphor. Herein, a series of novel (Li/Na/Cs)0.4Ba0.8SiF6:Mn4+ phosphors with optimized fluorescence properties induced by alkaline metal ions replacement are successfully synthesized via a green and eco-friendly approach. Under the irradiation of 460 nm blue light, Cs0.4Ba0.8SiF6:Mn4+ red phosphor with narrow band emission peak has the best optical performance. The optimal doping concentration of Mn4+ in Cs0.4Ba0.8SiF6 host and the reason for concentration quenching are systematically analyzed. Furthermore, the moisture resistance and thermal stability of this phosphor are discussed. After being soaked in deionized water for 90 min, the PL intensity of Cs0.4Ba0.8SiF6:Mn4+ phosphor can maintain at 40% of that in air, which is 4 times higher than commercial K2SiF6:Mn4+. At the operating temperature of LED (423 K), Cs0.4Ba0.8SiF6:Mn4+ red phosphor can exhibit stable light output intensity and color. A warm WLED with low correlated color temperature of 4336 K, high color rendering index of 88.4 and high lumen efficiency of 105.96 lm/W is fabricated via using Cs0.4Ba0.8SiF6:Mn4+ phosphor as a component of red-light, and the warm WLED can maintain stable output even at high driving currents. Overall, the alkali metal ion replacement and green synthesis strategies have opened up a new perspective for the synthesis of efficient Mn4+-doped fluoride phosphors, which has dual benefits for optimizing the performance of WLED and environmental protection.

Compositionally engineered vacancy-ordered double-perovskite nanocrystals for photovoltaic application

Lead-free double perovskites, in particular tin-based perovskites, have emerged to be a promising photo-absorber in solar cells for attaining protruding efficiency and stability. However, the tin-based double perovskite nanocrystals are yet to be investigated in photovoltaics. There are several advantages of nano-crystals over their bulk counterpart, including tunable band gap, higher fluorescence, and higher carrier lifetime, to name a few. In this work, we synthesized vacancy-ordered Cs2SnI6 nanocrystals (NC) and explored their potential in solar cell applications as a photo-absorber for the first time. Due to the 4+ oxidation state of Sn, this perovskite has a high stability against oxidation and hydrolysis during manufacturing and device operation. We also incorporated alkali-metal ion Rb+ in the Cs2SnI6 NCs for a possible enhancement of efficiency and stability in photovoltaic cells. Better carrier extraction was found through this incorporation as the optical band gap of the NCs is narrowed down to 1.39 eV. The Density Functional Theory (DFT) study revealed the change in the electronic band gap and density of states (DOS) of the NCs upon Rb-doping. The photovoltaic device fabricated with the FTO/TiO2/(Cs1−xRbx)2SnI6 NC/CuI/Au architecture has achieved a maximum efficiency of 0.71% with an inspiring short-circuit current (Jsc) of ∼5 mA/cm2. The champion cell has also shown remarkable stability after ∼40 days in an ambient atmosphere. This work, therefore, provides new insights into the alkali-metal ion regulated lead-free fully inorganic perovskite NCs for stable photovoltaic application.

Influence of Alkali Metal Ions on the Structural and Spectroscopic Properties of Sm3+-Doped Silicate Glasses

In the present work, the influence of alkali ions (Li, Na, K) on the structural and spectroscopic properties of silica glasses doped with Sm3+ was investigated. Infrared and Raman spectroscopy techniques were used to investigate the structural properties of the alkali silicate glasses. The optical absorption showed bands characteristic of Sm3+ ions in alkali silicate glasses, and this was investigated. The Judd–Ofelt theory was applied to evaluate the phenomenological intensity parameters (Ω2, Ω4, and Ω6) of the optical absorption measurements. The multi-channel visible and near infrared emission transitions originating from the 4G5/2-emitting state of the Sm3+ in alkali silicate glasses with a maximum phonon energy of ~1050 cm−1 were investigated. From the evaluated Judd–Ofelt parameters, radiative parameters such as spontaneous emission probabilities, radiative lifetimes, branching ratios, and stimulated emission cross-sections were calculated. The recorded luminescence spectra regions revealed intense green, orange, red, and near-infrared emission bands, providing new traces for developing tunable laser and optoelectronic devices.

Structure and compositional trends in alkali-metal containing titanium and vanadium oxide chalcogenides and the new van der Waals phase Ti2Te2O

We report the solid-state synthesis of all eighteen layered oxide chalcogenides in the structural family AM2Q2O (A = K/Rb/Cs; M = Ti/V; Q = S/Se/Te), allowing the determination of trends in composition and reactivity within the series. All materials are isostructural, crystallising in the primitive tetragonal space group P4/mmm as reported previously for five compounds in the series. The titanium or vanadium ions have intermediate valency on a single crystallographic site, leading to temperature-independent paramagnetism and correlated electronic behaviour which is influenced by the compositional variation. Furthermore, the alkali metal ions in ▪ and ▪ can be removed by oxidative deintercalation using ▪ at room temperature to produce a new metastable van der Waals layered phase, ▪. During the deintercalation reaction the oxide chalcogenide layers undergo a relative shift by (0.5,0.5) in the ab plane such that ▪ is body-centered with space group I4/mmm.