NMR, ESR, and Luminescence Characterization of Bismuth Embedded Zeolites Y

Thermal treatment of bismuth-embedded zeolite Y yields luminescent Bi⁺ substructures without the formation of metallic nanoparticles. The structural and photophysical features of the resulting zeolite Y have been thoroughly characterized by using extensive experimental techniques including nuclear magnetic resonance (NMR), electron spin resonance (ESR), 2-dimentional excitation–emission and absorption spectra. NMR and ESR results indicate that some Al and oxygen are expelled from the zeolite Y framework after undergoing thermal treatment. The detailed analyses of luminescence and absorption spectra, coupled with TDDFT calculations, suggest that all Bi⁺ substructures (i.e., Bi₄⁴⁺, Bi₃³⁺, Bi₂²⁺, and Bi⁺) are optically active in the near-infrared (NIR) spectral range. It is found that Bi⁺, Bi₂²⁺, Bi₃³⁺, and Bi₄⁴⁺ units result in NIR emissions peaking at ca. 1050, 1135, 1145, and 1240/1285 nm, respectively. The emission lineshapes under diverse excitation wavelengths greatly depend on the Bi concentration and annealing temperature, as a result of the change in the relative concentration and the spatial distribution, as well as local structural features of Bi active species. Specifically, the above analyses imply that the reducing agents for Bi³⁺ are water molecules as well as framework oxygen. These findings represent an important contribution to the understanding of the processes involved in the formation of Bi⁺ and of the luminescence mechanisms of Bi⁺ substructures in zeolite Y frameworks, which are not only helpful for the in-depth understanding of experimentally observed photophysical properties in other Bi-doped materials but also important for the development of novel photonic material systems activated by other p-block elements

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

Ce-Doped La₃Si_6.5Al_1.5N_9.5O_5.5, a Rare Highly Efficient Blue-Emitting Phosphor at Short Wavelength toward High Color Rendering White LED Application

Phase pure nondoped and Ce doped La₃Si_6.5Al_1.5N_9.5O_5.5 (Al containing La N-phase) samples have been obtained by solid-state reaction synthesis for the first time. 1% Ce-doped La₃Si_6.5Al_1.5N_9.5O_5.5 phosphor displays a broad excitation band ranging from UV to 410 nm, with a maximum at 355 nm. UV light excitation results in a narrow Ce³⁺ 5d-4f emission band (fwhm = 68 nm) centered at 418 nm. The emission can be tuned from 417 nm at 0.5% Ce to 450 nm at 50% Ce. A high internal quantum efficiency up to 84% is achieved for a 1% Ce doped sample, which has CIE chromaticity coordinates of <i>x</i> = 0.157 and <i>y</i> = 0.069, close to the NTSC blue standard (<i>x</i> = 0.155; <i>y</i> = 0.070). Compared to La₃Si₈O₄N₁₁:Ce phosphor, the quantum efficiency and thermal stability have been enhanced for La₃Si_6.5Al_1.5N_9.5O_5.5:Ce phosphor without shifting the emission peak wavelength. La₃Si_6.5Al_1.5N_9.5O_5.5:Ce shows less thermal quenching than La₃Si₈O₄N₁₁:Ce and no shift or change in the shape of emission spectra with increasing the temperature from 4 to 573 K. These results show that La₃Si_6.5Al_1.5N_9.5O_5.5:Ce is more efficient than any other (oxy-)­nitride phosphor with an emission in the short wavelength blue region (400–450 nm). A white LED was fabricated using the La₃Si_6.5Al_1.5N_9.5O_5.5:5Î as a blue phosphor. The high color rendering index (Ra = 93.2, R9 = 91.4, and R12 = 89.5) obtained shows that the phosphor is a very promising conversion phosphor for white LEDs

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