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The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na–Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na0.9Li0.1LuF4–Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future. [ABSTRACT FROM AUTHOR]

The luminescence and scintillation properties of Ce3+ doped alkali phosphate glasses 56P 2 O 5 :8Gd 2 O 3 :5Al 2 O 3 :1CeBr 3 :30XCl (PGAC:X, X = Li/Na/K/Rb/Cs) were studied for their potential applications in gamma and alpha detection. In the Fourier Transform Infrared Spectroscopy (FTIR), X-ray Luminescence (XRL), Photoluminescence (PL), and transmittance spectra, the red shift was found and explained by the concept of optical basicity. Broad Ce3+ emission and energy transfer from Gd3+ to Ce3+ were observed in XRL and PL measurements. Scintillation performance was studied by irradiating the samples under 137Cs gamma and 241Am alpha sources. The fast, intermediate, and slow decay components under gamma and alpha excitation were found around 30, 200 and 3000 ns, respectively. The decay time increased slightly from PGAC:Li to PGAC:Cs, indicating the less effective transition from Gd3+ to Ce3+. The alpha decay time was longer than the gamma decay time, revealing the Pulse Shape Discrimination (PSD) capability of the glasses for particle identification. The XRL intensity reduced significantly from PGAC:Li to PGAC:Cs samples did not reflect the scintillation tendency. By successfully detecting gamma and alpha scintillation signals, the scintillation performance of all samples was found to be similar. In general, all samples can be used for gamma and alpha detection. Using Rb+ or Cs+ ions is favorable in terms of high density and light yield, while Li+ ions enhance the transmittance and homogeneity. Furthermore, a correlation between P–O–H groups within the glass matrix and scintillation performance was also observed. [ABSTRACT FROM AUTHOR]

The mineral raw Egyptian kaolinite was used as a precursor in the synthesis of two sodalite phases (sodium sodalite (Na.SD) and potassium sodalite (K.SD)) according to the low alkali fusion technique. The synthesized Na.SD phase demonstrates enhanced total basicity (6.3 mmol OH/g), surface area (232.4 m2/g), and ion exchange capacity (126.4 meq/100 g) compared to the K.SD phase (217.6 m2/g (surface area), 96.8 meq/100 g (ion exchange capacity), 5.4 mmol OH/g (total basicity). The catalytic performance of the two sodalite phases validates the higher activity of the sodium phase (Na.SD) than the potassium phase (K.SD). The application of Na.SD resulted in biodiesel yields of 97.3% and 96.4% after 90 min and 60 min, respectively, while the maximum yield using K.SD (95.7%) was detected after 75 min. Robust base-catalyzed reactions using Na.SD and K.SD as catalysts were suggested as part of an operated transesterification mechanism. Moreover, these reactions exhibit pseudo-first order kinetics, and the rate constant values were estimated with consideration of the change in temperature. The estimated activation energies of Na.SD (27.9 kJ.mol−1) and K.SD (28.27 kJ.mol−1) reflected the suitability of these catalysts to be applied effectively under mild conditions. The essential thermodynamic functions, such as Gibb's free energy (65.16 kJ.mol−1 (Na.SD) and 65.26 kJ.mol−1 (K.SD)), enthalpy (25.23 kJ.mol−1 (Na.SD) and 25.55 kJ.mol−1 (K.SD)), and entropy (−197.7 J.K−1.mol−1 (Na.SD) and −197.8 J.K−1.mol−1 (K.SD)), display the endothermic and spontaneous nature of the two transesterification systems. [ABSTRACT FROM AUTHOR]

The effect of alkali ions (Na+ and K+) on the hydrothermal synthesis of olivine lithium metal phosphates in the P excess system was investigated by taking the synthesis of LiMn0.8Fe0.19Mg0.01PO4 as a case study. It is found that the coexisting Na+ can compete with Li+ to partly form NaMnPO4 as an impurity when the Na+/Li+ ratio exceeds the critical value, and this is not the case for the coexisting K+. These behaviors should be related to the difference in the ionic size of the alkali ions which also leads to a very different process of LiMn0.8Fe0.19Mg0.01PO4 formation. The samples derived from the K+‐coexisting reaction system can deliver much higher reversible capacities as compared with the sample derived from the Na+‐coexisting reaction system. This study provides new insights into the chemistry of the hydrothermal synthesis of olivine lithium metal phosphates, with an important implication for controllable synthesis and property manipulation. [ABSTRACT FROM AUTHOR]

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na+ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO 4 2− in the pore solution of SSC can inhibit the diffusion of OH−. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alkali ions pre-intercalated enlarges the interlayer distance of Ti 3 C 2 T x MXene. • DFT calculation shows that Na-MXene has the lowest Na+ diffusion energy barrier. • Na-MXene significantly improves sodium storage performance. Two-dimensional (2D) materials, Ti 3 C 2 T x MXene, have great potential for rapidly and stabilized sodium storage because of their excellent electrical conductivity and rich redox active sites. However, affected by the interaction of hydrogen bonds and van der Waals forces, Ti 3 C 2 T x MXene nanosheets are prone to collapse and re-stacking, which is not conducive to the ions diffusion and electrons transport, affects the electrochemical performance. Herein, we prepared 3D wrinkled Ti 3 C 2 T x MXene architectures with alkali ions (Na+, K+, Li+) pre-intercalation by continuous stirring treatment of Ti 3 C 2 T x MXene in aqueous borohydride (NaBH 4 , KBH 4 , LiBH 4) solution for sodium storage. This structure effectively enlarges the interlayer distance of Ti 3 C 2 T x MXene nanosheets and shortens the sodium ion diffusion path. Benefitting from the superiority of the structure, Na+ pre-intercalated Ti 3 C 2 T x MXene has the most excellent sodium storage performance, high reversible capacity of 256 mA h g−1 at 100 mA g−1 after 100 cycles, and amazing long-cycle stability of 168 mA h g−1 at 2000 mA g−1 after 6000 cycles. The density functional theory (DFT) calculation shows that the Ti 3 C 2 T x MXene pre-intercalating with Na+ significantly reduces the diffusion energy barrier, greatly improves the embedding and diffusion kinetics of Na+. This novel three-dimensional wrinkled Ti 3 C 2 T x MXene structure with alkali ions pre-intercalated can better broaden the application prospects of MXene-based materials in energy storage fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Study of alkali ions approaching an electrode surface. • The energetics follow the Hofmeister series. • Li+ and Na+ show signs of structure making. • K+ and Cs+ shows signs of structure breaking. The approach of alkali ions from an aqueous solution towards a gold electrode has been studied by biased molecular dynamics. In accord with the Hofmeister series, Li+ and Na+ show signs of structure making, K+ and Cs+ of structure breaking. For all ions the potential of mean force at first rises, when the ion approaches the surface, passes through a maximum and then drops again to a local minimum. For the structure breaking ions Cs+ and K+ the solvation energies in the minima are the same as in the bulk, for Na+ and Li+ they are a little higher. [ABSTRACT FROM AUTHOR]

Adsorption and exchange of ions on clay mineral surfaces are the fundamental processes which control the elemental partition in soil or marine sediments and the geological storage of toxic and radioactive waste. The distribution of ions at the surface has been modeled as an electric double layer. Due to the specificity of ions, simple theoretical models are hard to well predict ionic behaviors. Molecular dynamic simulations with empirical force fields to describe ionic interactions seem to be a delicate approach. However, different force fields for alkali ions were used when simulating clay mineral/water solution systems. It raises the question whether the empirical force field is reliable. We perform simulations with four generally used force fields for alkali ions (Na+, K+, and Cs+) to study cationic exchanges on the muscovite mica surface. Through comparing results to experimental thermodynamic data, we determine that the Horinek+SPC/E force field delivers the most consistent results. The adsorption and hydration structure of ions do not vary much as different force fields are used. However, it is this small variation in structure which explains the cationic affinity difference. This study sheds light on how to verify an ionic force field with which to reveal the clay surface phenomena and how to optimize force field parameters. • Simulations with different force fields for alkali ions to reveal ion exchanges on mica surface were performed. • The Horinek+SPC/E force field delivers the most consistent results with experiments. • Small variation in structure explains the cationic affinity difference with different force fields. • This study sheds light on force field development for studying clay surface phenomena. [ABSTRACT FROM AUTHOR]