Search results for "doping"
showing 10 items of 801 documents
The luminescence properties of ZnO nanopowders
2007
Pure and Al3+ doped ZnO nanopowders were studied by means of time-resolved luminescence spectroscopy. The powders were synthesized by hydrothermal and plasma methods. These powders were used as a raw material for vaporization-condensation process inside the Solar reactor. The commercially available ZnO nanopowder was studied for a comparison. Exciton to defect band luminescence intensity ratio was estimated in different types of ZnO nanopowders. It was found that nanopowders with whiskers morphology show superlinear luminescence intensity depending on excitation density. The observed effect depends on the average nanoparticle size and on the powder morphology.
Supercontinuum generation in Ge-doped Y-shaped microstructured tapered fiber
2011
We have investigated the generation of supercontinuum in tapered Y-shaped fibers in the nanosecond pump regime. This fiber used to fabricate the tapers has, in addition, a Ge-doped core which enhances the nonlinearity of the material and the Raman gain. The fiber was pumped at 1064 nm in the ns pump regime (0.6 ns pulses and up to 3.2 kW peak power). The taper had a uniform waist of 0.9 μm diameter and 130 mm length, and the adiabatic transitions were 110 mm long. A flat spectrum spanning from 420 nm to 1870 nm was obtained using a single tapered fiber.
Up-conversion process in erbium doped lithium fluoride bulk crystal, lithium borate glass and glass ceramics
2007
In our research the up-conversion processes in Er doped bulk LiF crystal, lithium borate oxyfluoride glass and lithium borate oxyfluoride glass ceramics were studied: up- conversion and traditional photoluminescence spectra, the up-converted signal as a function of the laser power are presented. It was found that sharp luminescence bands in the visible part of the spectrum appear when the bulk crystal is subjected to IR irradiation at 980 nm by a laser diode. After the heat treatment of the glass submicron crystallites were detected by SEM technique. The presence of LiF crystalline phase in the oxyfluoride glass ceramics was proved by XRD method. The questions about the synthesis of the oxy…
Anomalous behaviour of periodic domain structure in Gd-doped LiNbO3single crystals
2007
Atomic force microscopy studies of etching patterns, stability of regular domain structure, and anomalies of electrical characteristics in the 300 - 385 K range of a series of Gddoped lithium niobate single crystals grown under equal conditions are reported.
Absence of element specific ferromagnetism in Co doped ZnO investigated by soft X-ray resonant reflectivity
2010
On the quest for the intrinsic origin of ferromagnetism (FM) in ZnO doped with a few percent transition metal, we show detailed X-ray resonant magnetic reflectivity (XRMR) measurements, performed at the Co L2,3 and the O K edges of pulsed laser deposition (PLD) prepared samples. These samples show ferromagnetism at room temperature (RT) (QUID: about 2μB /Co). But in contrast to the QUID measurements, element specific reflection measurements as a function of angle (θ-2θ scans) and energy (const. qz) do not show any sign of ferromagnetism. Therefore, we can exclude without doubt Co as a possible origin for FM in this system. Our results are in perfect agreement with earlier published XMCD dat…
Optical active centres in ZnO samples
2006
Abstract In recent years, there has been a resurgence in the interest in the use of ZnO (Eg ∼ 3.37 eV) as a material for a wide range of opto-emitter applications spanning visible and short wavelengths. Bulk, thin films and nanomaterials obtained using different synthesis methods have been investigated for optoelectronic and biotechnological device applications. Nominally undoped bulk samples typically present a myriad-structured near-band-edge recombination, mainly due to free/bound excitons and donor–acceptor pair transitions. Furthermore, deep level emission due to intrinsic defects and extrinsic impurities, such as transition metal ions, are commonly observed in different grades of bulk…
Multicolor Up-Conversion Luminescence in Rare-Earth Doped NaLaF4
2011
In this work we tried to achieve multicolor up-conversion luminescence in low phonon energy material NaLaF4 doped with different Er3+ Tm3+ and Yb3+ concentrations. Up-conversion luminescence was measured and main luminescence bands from Er3+ and Tm3+ in red, green and blue spectral regions were observed. The relative intensities of the luminescence bands could be changed by changing the doping levels of rare-earth ions. Changes in the up-conversion luminescence color could be achieved by applying different infrared pump power density. The color coordinates of the multicolor up-conversion luminescence depending on doping level as well as on the pump power density were presented in CIE (x, y)…
Magnetic properties of MoS 2 nanotubes doped with lithium
2003
DC magnetization measurements of lithium-doped molybdenum sulfide nanotubes (LixMoS2, 2.2 10 kOe, the nonlinear part in H<5 kOe with saturation at approximately 10 kOe can be observed. This suggests a formation of ferromagnetic clusters even at room temperature. No magnetic phase transition between 2 and 300 K has been detected.
Theoretical EHT study of oxidative coupling of methane on pure MgO and MgO doped with Li and Na
1991
Abstract On the basis of Extended Huckel Theory, empirical studies on the oxidative coupling of methane with MgO pure and MgO doped with Li and Na are presented. The results obtained from the two-dimensional energy surfaces calculated for the interaction between linear clusters of these oxides and the methane molecule show a qualitative agreement with the experimental behaviour reported for these catalysts. The calculated activation energy barriers are in accord with the relative activities of these oxides (Li/MgO > Na/ MgO > MgO) and are of the same order of magnitude as the experimentally determined activation energies.
On the interest of ambipolar materials for gas sensing
2017
International audience; Based on the electrochemical properties of a series of metallophthalocyanines this article shows that the phthalocyanine bearing four alkoxy groups and twelve fluorine atoms behaves approximately as those with eight fluorine atoms. This indicates that the electron-donating effect of one alkoxy group balances the electro-withdrawing effect of one fluorine atom. We engaged three metallophthalocyanines, namely the octafluoro copper phthalocyanine, Cu(F8Pc), an octaester metallophthalocyanine and a phthalocyanine bearing four alkoxy groups and twelve fluorine atoms, Zn(T4F12Pc), in building original conductometric transducers that are Molecular Semiconductor – Doped Insu…