Size-Dependent Color Tuning of Efficiently Luminescent Germanium Nanoparticles

It is revealed that rigorous control of the size and surface of germanium nanoparticles allows fine color tuning of efficient fluorescence emission in the visible region. The spectral line widths of each emission were very narrow (<500 meV). Furthermore, the absolute fluorescence quantum yields of each emission were estimated to be 4–15%, which are high enough to be used as fluorescent labeling tags. In this study, a violet-light-emitting nanoparticle is demonstrated to be a new family of luminescent Ge. Such superior properties of fluorescence were observed from the fractions separated from one mother Ge nanoparticle sample by the fluorescent color using our developed combinatorial column technique. It is commonly believed that a broad spectral line width frequently observed from Ge nanoparticle appears because of an indirect band gap nature inherited even in nanostructures, but the present study argues that such a broad luminescence spectrum is expressed as an ensemble of different spectral lines and can be separated into the fractions emitting light in each wavelength region by the appropriate postsynthesis process

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

Synchrotron X-ray, Photoluminescence, and Quantum Chemistry Studies of Bismuth-Embedded Dehydrated Zeolite Y

For the first time, direct experimental evidence of the formation of monovalent Bi (i.e., Bi⁺) in zeolite Y is provided based on the analysis of high-resolution synchrotron powder X-ray diffraction data. Photoluminescence results as well as quantum chemistry calculations suggest that the substructures of Bi⁺ in the sodalite cages contribute to the ultrabroad near-infrared emission. These results not only enrich the well-established spectrum of optically active zeolites and deepen the understanding of bismuth related photophysical behaviors, but also may raise new possibilities for the design and synthesis of novel hybrid nanoporous photonic materials activated by other heavier p-block elements

Synchrotron X-ray, Photoluminescence, and Quantum Chemistry Studies of Bismuth-Embedded Dehydrated Zeolite Y

For the first time, direct experimental evidence of the formation of monovalent Bi (i.e., Bi⁺) in zeolite Y is provided based on the analysis of high-resolution synchrotron powder X-ray diffraction data. Photoluminescence results as well as quantum chemistry calculations suggest that the substructures of Bi⁺ in the sodalite cages contribute to the ultrabroad near-infrared emission. These results not only enrich the well-established spectrum of optically active zeolites and deepen the understanding of bismuth related photophysical behaviors, but also may raise new possibilities for the design and synthesis of novel hybrid nanoporous photonic materials activated by other heavier p-block elements

EDTA-assisted phase conversion synthesis of (Gd_0.95RE_0.05)PO₄ nanowires (RE = Eu, Tb) and investigation of photoluminescence

<p>Hexagonal (Gd_0.95RE_0.05)PO₄·<i>n</i>H₂O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd_0.95RE_0.05)₂(OH)₅NO₃·<i>n</i>H₂O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH₄H₂PO₄) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires. The hydrothermal products obtained up to 180 °C are of a pure hexagonal phase, while monoclinic phosphate evolved as an impurity at 200 °C. The nanowires undergo hexagonal→monoclinic phase transformation upon calcination at ≥600 °C to yield a pure monoclinic phase at ~900 °C. The effects of calcination on morphology, excitation/emission, and fluorescence decay kinetics were investigated in detail with (Gd_0.95Eu_0.05)PO₄ as example. The abnormally strong ⁵D₀→⁷F₄ electric dipole Eu³⁺ emission in the hexagonal phosphates was ascribed to site distortion. The process of energy migration was also discussed for the optically active Gd³⁺ and Eu³⁺/Tb³⁺ ions.</p