Theoretical Insights into the ²⁷Al NMR Parameters of Binary Aluminosilicate Glass and Their Relationship to the Atomic and Electronic Structure

Al-rich 60Al2O3–40SiO2 glass is a candidate for technological applications in electronic and optical devices. Though the amorphous structure of the glass has been studied using solid-state NMR and simulation approaches, the atomic and electronic structure have not been fully revealed. Solid-state 27Al NMR spectra reflect the 27Al environment, though a comprehensive understanding of the spectra and local structure is challenging when interpreting the broadened peak shapes of the amorphous state. Here, an accurate atomic structure of 60Al2O3–40SiO2 glass was modeled using ab initio molecular dynamics (AIMD) simulations containing 418 atoms and employing the melt-quenching route with 15 K/ps. This simulation approach reproduced X-ray diffraction data better than classical molecular dynamics (CMD) simulations. The structure of the polyhedra formed by O bonded to Al was quantitatively analyzed by evaluating bond-angle distributions and the degree of symmetry using spherical harmonic functions. The relationship between chemical shifts and charge-balancing mechanisms was explored through the analysis of electronic structures obtained from AIMD-derived structures. Interestingly, the Al partial charge and the spatial electron distribution of Al–O bonds were independent of the Al coordination number, implying that valence electrons are not localized to specific atoms but are rather distributed throughout the glass network. The theoretical distribution of 27Al NMR parameters was obtained through statistical analysis of theoretically calculated NMR parameters for 100 AIMD-derived structures. By comparing the experimental 27Al NMR data with the theoretical distribution, the previously unclear relationship between 27Al NMR parameters and local structure was elucidated

Theoretical Insights into the ²⁷Al NMR Parameters of Binary Aluminosilicate Glass and Their Relationship to the Atomic and Electronic Structure

Al-rich 60Al2O3–40SiO2 glass is a candidate for technological applications in electronic and optical devices. Though the amorphous structure of the glass has been studied using solid-state NMR and simulation approaches, the atomic and electronic structure have not been fully revealed. Solid-state 27Al NMR spectra reflect the 27Al environment, though a comprehensive understanding of the spectra and local structure is challenging when interpreting the broadened peak shapes of the amorphous state. Here, an accurate atomic structure of 60Al2O3–40SiO2 glass was modeled using ab initio molecular dynamics (AIMD) simulations containing 418 atoms and employing the melt-quenching route with 15 K/ps. This simulation approach reproduced X-ray diffraction data better than classical molecular dynamics (CMD) simulations. The structure of the polyhedra formed by O bonded to Al was quantitatively analyzed by evaluating bond-angle distributions and the degree of symmetry using spherical harmonic functions. The relationship between chemical shifts and charge-balancing mechanisms was explored through the analysis of electronic structures obtained from AIMD-derived structures. Interestingly, the Al partial charge and the spatial electron distribution of Al–O bonds were independent of the Al coordination number, implying that valence electrons are not localized to specific atoms but are rather distributed throughout the glass network. The theoretical distribution of 27Al NMR parameters was obtained through statistical analysis of theoretically calculated NMR parameters for 100 AIMD-derived structures. By comparing the experimental 27Al NMR data with the theoretical distribution, the previously unclear relationship between 27Al NMR parameters and local structure was elucidated

N‑Dopant Site Formulation for White-Light-Emitting Carbon Dots with Tunable Chromaticity

Multicolor emissions from carbon dots (CDs) are vital for light-emitting diodes (LEDs), particularly for direct, white-light emission (WLE), which enables a replacement of rare earth (RE)-doped phosphors. However, the difficulty of synthesizing single-component WLE CDs with full-spectrum emission severely hinders further investigation of their emission mechanisms and practical applications. Here, we demonstrate rational design and synthesis of chromatically tunable CDs with cyan-, orange-, and white-light emission, precisely tunable along the blackbody Planckian locus by controlling the ratio of different nitrogen dopant sites. We adopted 15N solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to identify and quantify N-dopants in different sites and environments, and we explain their influence on emission properties of these CDs. This study provides guiding principles to achieve spectrally tuned emissions, enabling us to design WLE from CDs. This study also clarifies which chemical reagents and their proportions should be used for solvothermal synthesis to realize well-defined WLE from single-component CDs and adjustable, correlated color temperature (CCT) from 6500 to 3500 K. We also demonstrate a soft lighting device by adopting an optical haze film composed of cellulose fibers with excellent light-tailoring characteristics. The proposed methodology for synthesizing WLE CDs by engineering the N-doping sites will boost the development of lighting devices with readily available materials toward realization of low-cost, environmentally friendly WLEDs, solar cells, UV-blockers, counterfeit inks, and display applications

Dynamic Breathing of CO₂ by Hydrotalcite

The carbon cycle of carbonate solids (e.g., limestone) involves weathering and metamorphic events, which usually occur over millions of years. Here we show that carbonate anion intercalated layered double hydroxide (LDH), a class of hydrotalcite, undergoes an ultrarapid carbon cycle with uptake of atmospheric CO₂ under ambient conditions. The use of ¹³C-labeling enabled monitoring by IR spectroscopy of the dynamic exchange between initially intercalated ¹³C-labeled carbonate anions and carbonate anions derived from atmospheric CO₂. Exchange is promoted by conditions of low humidity with a half-life of exchange of ∼24 h. Since hydrotalcite-like clay minerals exist in Nature, our finding implies that the global carbon cycle involving exchange between lithosphere and atmosphere is much more dynamic than previously thought

Naked-Eye Discrimination of Methanol from Ethanol Using Composite Film of Oxoporphyrinogen and Layered Double Hydroxide

Methanol is a highly toxic substance, but it is unfortunately very difficult to differentiate from other alcohols (especially ethanol) without performing chemical analyses. Here we report that a composite film prepared from oxoporphyrinogen (OxP) and a layered double hydroxide (LDH) undergoes a visible color change (from magenta to purple) when exposed to methanol, a change that does not occur upon exposure to ethanol. Interestingly, methanol-induced color variation of the OxP-LDH composite film is retained even after removal of methanol under reduced pressure, a condition that does not occur in the case of conventional solvatochromic dyes. The original state of the OxP-LDH composite film could be recovered by rinsing it with tetrahydrofuran (THF), enabling repeated usage of the composite film. The mechanism of color variation, based on solid-state ¹³C–CP/MAS NMR and solution-state ¹³C NMR studies, is proposed to be anion transfer from LDH to OxP triggered by methanol exposure