Search results for "Cathodoluminescence"
showing 10 items of 61 documents
Cathodoluminescence and IR absorption of oxygen deficient silica – influence of hydrogen treatment
1999
Abstract The cathodoluminescence (CL) and IR absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, some samples have been treated in hydrogen at 800°C. Crystalline quartz was used for reference measurements and the CL data have been compared with those of X-ray excited luminescence (XL). The luminescence spectra of silica have a band at 1.85 eV due to non-bridging oxygens and the two bands at 2.7 and 4.4 eV due to twofold-coordinated silicons. The energetic yield for CL is about 0.1%, for XL it approaches 0.15%. Cathodoluminescence of quartz at temperatures >130 K exhibits the self-trapped exciton lumines…
Radiation induced defects in SiO 2
2002
The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) …
Cathodoluminescence mechanism of crystalline Gd2SiO5:Ce
1993
Complex luminescence decay kinetics have been observed in Gd2SiO5:Ce crystals under electron beam irradiation. Absorption and photoluminescence excitation spectra, decay kinetics in various excitation bands over a wide range of photon energies from 3.6 to 7.0 eV in the temperature region from 80 to 400 K as well as the spectra of the glow curve creation efficiency at 80 K are examined. It is shown that the free electronic excitations produced, depending on the absorbed photon energy, have different recombination mechanisms finally leading to the radiative transitions between the 5d2E configuration and the 4f configuration of the Ce3+ ion. At hvexc < 6.1 eV a single exponential decay caused …
UV cathodoluminescence of crystalline α-quartz at low temperatures
2004
Two luminescence bands in the UV range were detected in crystalline a-quartzunder electron beam excitation (6 kV, 3–5mA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (o10 ns) and a slow one in the range of 200ms. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline a-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation me…
Luminescent properties of GaN films grown on porous silicon substrate
2010
Abstract GaN films have been grown on porous silicon at high temperatures (800–1050 °C) by metal organic vapor phase epitaxy. The optical properties of GaN layers were investigated by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. PL spectra recorded at 5 K exhibit excitonic emissions around 3.36–3.501 eV and a broad yellow luminescence at 2.2 eV. CL analysis at different electron excitation conditions shows spatial non-uniformity in-depth of the yellow and the band-edge emissions. These bands of luminescence are broadened and red- or blue-shifted as the electron beam penetrates in the sample. These behaviors are explained by a change of the fundamental band gap due to re…
Exciton luminescence of boron nitride nanotubes and nano-arches
2006
We report photoluminescence (PL) and PL-excitation spectroscopy of BN nanotubes (nt-BN) mixed with some residual hexagonal crystalline (h-BN) starting material, and of pure h-BN microcrystalline powder. The nanotube phase exhibits a broad-band PL near 380 nm, in agreement with a published report of cathodoluminescence from a sample comprising >90% nanotubes. This emission is almost 3 eV lower in energy than unrelaxed exciton states found in recent all-electron theories of nt-BN and h-BN and about 1.4 eV lower than the lowest (perturbed dark?) exciton seen in absorption of nt-BN. This may suggest that excitons in nt-BN vibrationally relax to self-trapped states before emitting, a path found …
Cathodoluminescence and photoluminescence study of plastically deformed ZnTe bulk single crystals
2001
Samples of zinc telluride bulk single crystals, which were deformed in uniaxial compression, have been studied by photoluminescence (PL) and cathodoluminescence (CL). As a particular feature the deformed samples present a PL emission band peaked at 603 nm, whose intensity increases as the plastic deformation does. This band is related to the density of dislocations produced during the interaction of slip systems. This hypothesis is supported by CL images. which reveal the activation of the successive slip systems corresponding to different levels of deformation.
Fast Luminescence Studies of NaLaF4: Pr3+ Glass Ceramics
2021
Cathodoluminescence (CL) emission and photoluminescence (PL) emission and excitation spectra of $16\mathbf{Na}2\mathbf{O}-9\mathbf{NaF}-5\mathbf{LaF}_{3}-7\mathbf{Al}_{2}\mathbf{O}_{3}-63\mathbf{SiO}_{2}$ (mol%) activated with 3% $\mathbf{PrF}_{3}$ , hereinafter referred to as $\mathbf{NaLaF}_{4}:\mathbf{Pr}_{9}^{3+}$ have been investigated. In particular, CL spectra were measured with time resolution after excitation with a 120 keV electron beam. The characteristic Pr3+ ion emission with fast decay times $\tau_{1}=1.77$ ns and $\tau_{2}=52.97$ ns at peak intensity at 406 nm were observed, which correspond well to the emission bands of the $\mathbf{Pr}^{3+}$ ion in other luminescent materia…
Luminescence of fluorine doped silica glass
2003
Abstract The role of fluorine doping on silica properties was studied by luminescence methods. Non-doped samples of the same preparation technology possess an absorption band at 7.6 eV on the level of 2 cm−1. A trace of this band in the fluorine-doped sample is on the level of 0.1 cm−1. In both samples 7.6 eV photons as well as ionizing irradiation (X-ray, electron beam) excite photoluminescence of so-called oxygen deficient centers with a blue (2.7 eV) and a UV band (4.4 eV). The luminescence of the fluorine doped sample increases with dose many times from the initial low level for the same excitation. Also, thermally stimulated luminescence appears after irradiation. The energetic yield u…
Luminescence study of defects in synthetic as-grown and HPHT diamonds compared to natural diamonds
2005
The optically active defects in as-grown, high-pressure high-temperature-treated (HPHT), boron-doped, and synthetic diamonds (SD) grown with a nitrogen-getter, as well as of natural diamonds (ND), were characterized by absorption and luminescence spectroscopies using different excitation sources. The laser-excited photoluminescence (PL) spectra of SDs show numerous sharp lines characteristic for nickel-related centers, whereas NDs yield mainly broad PL bands. The emission from the nickel-related defects in NIR range increases and the maxima of the bands shift to lower energies with increasing temperature. Under UV and electron beam excitation, the yellow synthetic diamonds display green lum…