Search results for "Photoluminescence"
showing 10 items of 811 documents
Ceria/polymer nanocontainers for high-performance encapsulation of fluorophores
2019
We report the synthesis of high-performance organic–inorganic hybrid fluorescent nanocapsules comprising a polymer shell armored with an inorganic layer and a liquid core containing a fluorophore. The polymeric capsules are synthesized by free radical miniemulsion polymerization and contain covalently bound carboxylate surface functionalities that allow for the binding of metal ions through electrostatic interaction. A cerium(IV) oxide nanoparticle layer, formed in situ at the surface of the hybrid nanocapsules, acts as oxygen scavenger and keeps external reactive molecular oxygen from entering into the capsules, eventually resulting in a reduction of the photooxidation of encapsulated fluo…
Quantum chemical modelling of electron polarons and green luminescence in PbTiO3perovskite crystals
2002
In an extension of our previous study on the electron polarons and excitons in KNbO3, KTaO3 and BaTiO3 (Kotomin E A, Eglitis R I and Borstel G 2000 J. Phys. Condens. Matter 12 L557; Eglitis R I, Kotomin E A and Borstel G 2002 J. Phys. Condens. Matter 14 3735) by the semiempirical Hartree–Fock method we present here results for free electron polarons in the PbTiO3 perovskite crystal. We discuss the origin of the intrinsic visible band emission of PbTiO3 perovskite oxides (so-called 'green luminescence') which has remained a topic of high interest during the last quarter of a century. We present a theoretical calculation modelling this emission in the framework of a concept of charge transfer…
Inhomogeneous free-electron distribution in InN nanowires: Photoluminescence excitation experiments
2010
Photoluminescence excitation (PLE) spectra have been measured for a set of self-assembled InN nanowires (NWs) and a high-crystalline quality InN layer grown by molecular-beam epitaxy. The PLE experimental lineshapes have been reproduced by a self-consistent calculation of the absorption in a cylindrical InN NW. The differences in the PLE spectra can be accounted for the inhomogeneous electron distribution within the NWs caused by a bulk donor concentration $({N}_{D}^{+})$ and a two-dimensional density of ionized surface states $({N}_{ss}^{+})$. For NW radii larger than 30 nm, ${N}_{D}^{+}$ and ${N}_{ss}^{+}$ modify the absorption edge and the lineshape, respectively, and can be determined f…
Radiation induced generation of non-bridging oxygen hole center in silica: Intrinsic and extrinsic processes
2007
Abstract The generation of non-bridging oxygen hole center ( Si–O ) was investigated in a wide variety of natural (fused quartz) and synthetic silica samples exposed to different γ- and β-irradiation doses by looking at its optical bands. We distinguish two different generation processes: intrinsic associated with the cleavage of Si–O bond and characterized by a sublinear law and extrinsic due to the conversion of OH precursor characterized by a growth curve with a saturating tendency. The interplay between the two processes and the role of H are discussed.
Multiexciton complex from extrinsic centers in AlGaAs epilayers on Ge and Si substrates
2013
The multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device. © 2013 AIP Publishing LLC.
Indium surfactant effect on AlN/GaN heterostructures grown by metal-organic vapor-phase epitaxy: Applications to intersubband transitions
2006
We report on a dramatic improvement of the optical and structural properties of AlN/GaN multiple quantum wells (MQWs) grown by metal-organic vapor-phase epitaxy using indium as a surfactant. This improvement is observed using photoluminescence as well as x-ray diffraction. Atomic force microscopy shows different surface morphologies between samples grown with and without In. This is ascribed to a modified relaxation mechanism induced by different surface kinetics. These improved MQWs exhibit intersubband absorption at short wavelength (2 mu m). The absorption linewidth is as low as 65 meV and the absorption coefficient is increased by 85%.
Mid-infrared intersubband absorption in lattice-matched AlInN/GaN multiple-quantum wells
2005
We report the observation of midinfrared intersubband (ISB) absorption in nearly lattice-matched AlInNGaN multiple-quantum-wells. A clear absorption peak is observed around 3 μm involving transitions from the conduction band ground state to the first excited state. In addition to ISB absorption, photoluminescence experiments were carried out on lattice- matched AlInNGaN single quantum wells in order to determine the spontaneous polarization discontinuity between GaN and Al0.82 In0.18 N compounds. The experimental value is in good agreement with theoretical predictions. Our results demonstrate that the AlInNGaN system is very promising to achieve crack-free and low dislocation density struct…
Luminescence of different modifications of crystalline silicon dioxide: Stishovite and coesite
2003
Abstract Luminescence of very small samples of single crystals of coesite and stishovite has been studied. The spectra were detected under ionizing radiation (X-ray and electron beam) and the decay kinetics of cathodoluminescence in the range of time from 10 ns to 3 ms was measured. The coesite luminescence possesses a broad band at 3 eV with exponential decay about 680 μs at 80 K. The nature of this luminescence was explained as a self-trapped exciton creation in tetrahedron framework. The stishovite luminescence possesses two bands—blue (2.8 eV) and UV (4.7 eV). The UV band intensity grows more than 20 times with irradiation dose from initial level. This shows that the corresponding lumin…
EXCITONS, LOCALIZED STATES IN SILICON DIOXIDE AND RELATED CRYSTALS AND GLASSES
2000
The excitons, localized states in crystalline and glassy silicon dioxide, germanium dioxide were studied by photoluminescent and photoelectric experimental methods. Results were compared with analogous investigations of related crystals, such as aluminum and gallium orthophosphates, and of related glasses, such as silica, sodium silicates, germanates, lead and phosphates glasses. Special attention was made to the influence of oxygen deficiency on localized states of glasses, in general, and to the nature of the 7.6 eV band in reduced silica, in particular.
Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals
2006
Abstract The luminescence of GeO 2 rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N 2 laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses…