Models of the self-trapped exciton and nearest-neighbor defect pair in SiO2

Promotion in solid phase reaction of Pt/SiOx bilayer film by electron-orbital-selective-excitation

A thermally impossible positive free energy reaction can proceed by electron-orbital-selective excitation. When the Si 2p core level is photo-excited in Pt/SiO_x bilayer films, Coulomb repulsion at the final two-hole state localized in the valence band by an interatomic Auger transition induces dissociation of the O atom and formation of a Si–Pt bond. Consequently, Pt₂Si silicide is formed by a positive free energy reaction. Under a single particle excitation of the valence band, low probability of the coexistence of the two-hole state for picosecond order suppresses to allow the reaction to proceed.

A thermally impossible positive free energy reaction can proceed by electron-orbital-selective excitation.

IR femtosecond laser micro-filaments in diamond visualized by inter-band UV photoluminescence

Single microscale filaments were produced in monocrystalline Ia-type diamond by 1030 nm, 300 fs laser pulses tightly focused at NA = 0.3 and different peak powers, visualized by transverse imaging and spectrally characterized by longitudinal micro-spectroscopy, using intrinsic UV A-band photoluminescence (PL) with its peak at about 430 nm. Power-dependent scaling relationships for the local PL yield and diameters of the accompanying luminous micro-channels of recombining electron-hole plasma indicate a transition from three-photon absorption to free-carrier plasma absorption, as the consequent energy deposition mechanisms at increasing peak laser power. Power-dependent elongation of the luminous micro-channels versus peak laser power fitted by a Marburger formula yields, on average a diffraction-based estimate of 0.6 MW critical power for self-focusing within the diamond at the pump laser wavelength of 1030 nm.

Nanoscale Transformations in Metastable, Amorphous, Silicon-Rich Silica

Electrically biasing thin films of amorphous, substoichiometric silicon oxide drives surprisingly large structural changes, apparent as density variations, oxygen movement, and ultimately, emission of superoxide ions. Results from this fundamental study are directly relevant to materials that are increasingly used in a range of technologies, and demonstrate a surprising level of field-driven local reordering of a random oxide network.

Luminescence properties of the pink emitting persistent phosphor Pr3+-doped La3GaGe5O16

The pink persistent phosphor La₃GaGe₅O₁₆:Pr³⁺ was prepared successfully via a traditional solid state reaction method.

One-step Melt Synthesis of Water Soluble, Photoluminescent, Surface-Oxidized Silicon Nanoparticles for Cellular Imaging Applications

We have developed a versatile, one-step melt synthesis of water-soluble, highly emissive silicon nanoparticles using bi-functional, low-melting solids (such as glutaric acid) as reaction media. Characterization through transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy shows that the one-step melt synthesis produces nanoscale Si cores surrounded by a silicon oxide shell. Analysis of the nanoparticle surface using FT-IR, zeta potential, and gel electrophoresis indicates that the bi-functional ligand used in the one-step synthesis is grafted onto the nanoparticle, which allows for tuning of the particle surface charge, solubility, and functionality. Photoluminescence spectra of the as-prepared glutaric acid-synthesized silicon nanoparticles show an intense blue-green emission with a short (ns) lifetime suitable for biological imaging. These nanoparticles are found to be stable in biological media and have been used to examine cellular uptake and distribution in live N2a cells.

New Polaronic-Type Excitons in Ferroelectric Oxides: INDO-Calculations and Experimental Manifestation

The current experimental and theoretical knowledge of new polaronic-type excitons in ferroelectric oxides – charge transfer vibronic excitons (CTVE) – is discussed. It is shown that Hartree-Fock-type INDO calculations as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE-concept. Single CTVE as well as a new phase of strongly correlated CTVEs are analysed.

Self-trapped excitons in silicon dioxide: mechanism and properties

Irradiating silica produces self-trapped excitons (STEs) that spontaneously create atomic-scale distortions on which they localize themselves. Despite enduring interest in STEs and subsequent defects in this key technological material, the trapping mechanism and geometry remain a mystery. Our ab initio study of STEs in alpha-quartz using a many-electron Green's function approach answers both questions. The STE comprises a broken O-Si bond with the hole localized on the defected oxygen and the electron on the defected silicon atom in a planar sp2 conformation. The results further explain quantitatively the measured STE spectra.

Optical emission from C60-molecule-coupled Si nanocrystallites

Using C60 molecule as a kind of surface-passivated agent to modify the electronic structure of Si nanocrystallites in porous silicon, we disclose that this kind of C60/nanocrystalline Si coupling system can show a strong blue emission at approximately 460 nm when stored in air for more than one year. After a full characterization of the photoluminescence properties, we propose a luminescent center in the SiOx layer at the surface of a Si nanocrystallite. It is a pair consisting of an oxygen vacancy and an interstitial oxygen. The interstitial oxygen also forms a peroxy linkage with a neighboring lattice oxygen. Radiative recombination of carriers photogenerated from Si nanocrystallite cores in the luminescent centers results in the observed blue photoluminescence. Neutron irradiation experiments support our assignment of the blue emission mechanism. This work improves the understanding of the origin of blue emission from silicon/oxygen-related nanostructured materials.