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Defect Centers (defect + center)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Defect structure and spectroscopic characteristics of codoped Hf: Er: LiNbO3 crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2009
Liang Sun
Abstract Codoped Hf: Er: LiNbO3 crystals have been grown by the Czochralski technique. Defect structures of the crystals were analyzed by IR absorption spectra, and the compositions of the crystals were measured by X-ray fluorescent spectrograph. A new OH, -associated vibrational peak at 3492 cm,1 was revealed in 6 mol % Hf: 1 mol % Er: LiNbO3 crystal. It was attributed to (HfNb), -OH, -(ErNb)2, defect centers. The Er3+ concentrations in crystals gradually decreased with the increase of the codoped Hf4+ concentrations in the melts. The emission characteristics of the crystals were investigated by the fluorescence spectrum. It was found that the luminescent intensity in codoped 6 mol % Hf: 1 mol % Er: LiNbO3 crystal was 3.5 times stronger than that in single doped 1 mol % Er: LiNbO3 crystal. The luminescent enhancement effect was successfully explained on the basis of defect structure of the crystals. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and photoluminescence properties of silicon nanowires treated by high-pressure water vapor annealing

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007
B. Salhi
Abstract This paper reports on silicon nanowires (SiNWs) growth on porous silicon (PS) template using vapor-liquid-solid (VLS) technique and the effect of high-pressure water vapor annealing (HWA) on their optical properties. Gold nanoparticles (Au NPs) with average mean diameter of 50 and 20 nm were used as catalysts. The SiNWs were obtained by thermal decomposition of silane gas (SiH4) at high temperature (540 °C) catalyzed by the Au NPs. The resulting nanostructures display comparable diameter to the initial gold catalysts and are few microns long without a preferential growth direction. We have next examined the optical properties of the 20 nm diameter SiNWs. As-prepared SiNWs display a weak photoluminescence (PL), which is related to the recombination emissions from defect centers. High-pressure water vapor annealing (HWA) at 260 °C and 2.6 MPa of the SiNWs led to an increase of the PL by a factor 10 without significant changes in the emission band. TEM analysis of the HWA-treated SiNWs showed a crystalline silicon core surrounded by an amorphous oxide layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cathodoluminescence properties of zinc oxide nanoparticles

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2004
M. R. Phillips
Abstract Zinc oxide nano-particles (25 nm) have been investigated by cathodoluminescence spectroscopy (300 nm,1700 nm) at 80 K and 300 K following thermal annealing in high purity H2/N2, N2, O2 and Ar gaseous atmospheres. The intensity of the ZnO near band edge peak was significantly increased after heat treatment in hydrogen. Conversely, thermal annealing in the other gas types decreased this emission. This effect is attributed to hydrogen passivation of competitive non-radiative defect centers, most likely bulk zinc vacancy centers. The appearance of a strong green emission centered at 2.4 eV following thermal annealing in all gas atmospheres is ascribed to the formation of bulk oxygen vacancy defects. A strong red shift of the near band edge emission with increasing beam current at 300 K is accredited to electron beam heating rather than to an increase in the carrier density. Electron beam heating is evidenced by the occurrence of a strong black body emission in the near infrared spectral region. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermoluminescence of LiF and F2 color centers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
G. Baldacchini
Abstract Light emitted when heating crystalline materials previously exposed to ionizing radiation is commonly known as thermoluminescence. The resultant glow curve is related to the material, the impurities and the defect centers generated by the irradiation. Several efforts have been made in the past to associate glow peaks with specific defect centers. Recently, in the case of LiF we established a link between F3+ and F3 centers and the temperature region of the glow curve below 200 °C. This result was obtained by using especially treated samples with known concentration of color centers in first place, and annealing measurements in second place. By continuing these studies, it has been possible to establish a further link between F2 centers and a prominent feature of the glow curve near 260 °C. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electron beam induced defects in Ge-implanted SiO2 layers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
Roushdey Salh
Abstract Scanning electron microscopy (SEM) and cathodoluminescence (CL) have been used to investigate the irradiation-sensitive defect structure of pure and Ge+ -implanted amorphous silicon dioxide layers. CL emission spectra at specimen temperatures between liquid nitrogen (LNT) and room temperature (RT) are identified with particular defect centers including the nonbridging oxygen-hole center (NBOHC: ,Si,O,) associated with the red luminescence at 650 nm (1.9 eV), the self trapped exciton (STE) with the yellow-green luminescence at 580 nm (2.1 eV) and the Si related oxygen deficient center (SiODC) with the blue (460 nm; 2.7 eV) and ultraviolet UV band (295 nm; 4.2 eV). In Ge doped SiO2 an additional emission band is identified at (410 nm; 3.1 eV). This band corresponds to the Ge related oxygen deficient center (GeODC). The annealing process of Ge+ -implanted layer leads first to a strong increase of the violet luminescence due to formation of Ge dimers, trimers and higher aggregates, finally to destruction of the luminescence centers by further growing to Ge nanoclusters. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]