Search results for "Doping"
showing 10 items of 801 documents
Evolution of Free Volumes in Polycrystalline BaGa2O4 Ceramics Doped with Eu3+ Ions
2021
H.K. and Y.K. would like to thank A. Ingram for assistance in PAL experiments. The authors thank E.A. Kotomin and M. Brik for the many useful discussions. The research was (partly) performed in the Institute of Solid State Physics, University of Latvia ISSP UL. ISSP UL as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project.
Photocatalytic and photothermocatalytic applications of cerium oxide-based materials
2020
Abstract Cerium dioxide (CeO2) presents unique properties as the special electronic and optical properties of the 4f electrons, the capacity to form nonstoichiometric oxygen-deficient CeO2 − x oxides, the high oxygen mobility, and the reversible transformation between Ce4 + and Ce3 + that make it interesting for photocatalytic applications. CeO2 is a wide bandgap semiconductor (3.0–3.4 eV), but different approaches as combination with oxides, deposition of noble metals, doping with metal and nonmetal species, and the formation of surface defects have been adopted to extend its absorption towards the visible region with the aim to improve its photocatalytic performance. Cerium oxide-based ma…
Infrared study of the MoO3 doping efficiency in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP)
2013
AbstractElectrochemical doping produces clear changes in the vibrational spectra of organic semiconductors as we show here for the system molybdenum oxide (MoO3) doped into the charge transport material 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP). Based on density-functional theory (DFT) calculations of vibrational spectra, the new spectral features can be attributed to the CBP cation that forms as a result of electron transfer from CBP to MoO3. The intensity of the new vibrational lines is a direct measure for the probability of charge transfer. MoO3 agglomerating within the CBP matrix limits the active interface area between the two species. The appearance of a broad electronic transition …
Nanoscale ear drum: graphene based nanoscale sensors.
2012
The difficulty in determining the mass of a sample increases as its size diminishes. At the nanoscale, there are no direct methods for resolving the mass of single molecules or nanoparticles and so more sophisticated approaches based on electromechanical phenomena are required. More importantly, one demands that such nanoelectromechanical techniques could provide not only information about the mass of the target molecules but also about their geometrical properties. In this sense, we report a theoretical study that illustrates in detail how graphene membranes can operate as nanoelectromechanical mass-sensor devices. Wide graphene sheets were exposed to different types and amounts of molecul…
A new monomeric interpretation of intrinsic optical bistability observed in Yb3+-doped bromide materials
2003
We present a mechanism able to show intrinsic bistable behaviour involving single Yb3+ ions embedded into bromide lattices, in which intrinsic optical bistability (IOB) has been observed. The mechanism is based on the experimentally found coupling between the Yb3+ ion and the totally symmetric local mode of vibration of the [YbBr6]3- coordination unit. The model reproduces the IOB observed in CsCdBr3:1% Yb3+ and allows to understand the experimentally found presence of the phenomenon in the other bromides, but its absence in Cs3Lu2Cl9:Yb3+.
A hollow tetrahedral cage of hexadecagold dianion provides a robust backbone for a tuneable sub-nanometer oxidation and reduction agent via endohedra…
2007
We show, via density functional theory calculations, that dianionic Au16(2-) cluster has a stable, hollow, Td symmetric cage structure, stabilized by 18 delocalized valence electrons. The cage maintains its robust geometry, with a minor Jahn-Teller deformation, over several charge states (q = -1,0,+1), forming spin doublet, triplet and quadruplet states according to the Hund's rules. Endohedral doping of the Au16 cage by Al or Si yields a geometrically robust, tuneable oxidation and reduction agent. Si@Au16 is a magic species with 20 delocalized electrons. We calculate a significant binding energy for the anionic Si@Au16/O2- complex and show that the adsorbed O2 is activated to a superoxo-s…
First-principles study of nitrogen doping in cubic and amorphous Ge2Sb2Te5
2011
We investigated the structural, electronic and vibrational properties of amorphous and cubic Ge(2)Sb(2)Te(5) doped with N at 4.2 at.% by means of large scale ab initio simulations. Nitrogen can be incorporated in molecular form in both the crystalline and amorphous phases at a moderate energy cost. In contrast, insertion of N in the atomic form is very energetically costly in the crystalline phase, though it is still possible in the amorphous phase. These results support the suggestion that N segregates at the grain boundaries during the crystallization of the amorphous phase, resulting in a reduction in size of the crystalline grains and an increased crystallization temperature.
Recombination processes in rare-earth doped MAl2O4(M = Ca, Sr) persistent phosphors investigated by optically-detected magnetic resonance
2007
Single crystalline MAl 2 O 4 (M = Ca and Sr) persistent phosphors, which are nominally pure or additionally doped with Eu and Nd or Dy, respectively, were investigated for their recombination luminescence (RL) and microwave-induced changes in the RL at low temperatures. The analysis of the optically-detected electron paramagnetic resonance (EPR) spectra, recorded after ultraviolet excitation at 4.2 K, shows that intrinsic donor and acceptor centres are involved in the recombination process. Spectral dependent RL-EPR measurements on undoped CaAl 2 O 4 (CAO) and SrAl 2 O 4 (SAO) show that we deal with only one donor but at least two different acceptors. The g value of the donor is 1.99 in CAO…
Eu2+ Stabilization in YAG Structure: Optical and Electron Paramagnetic Resonance Study
2016
A set of Eu-doped Y3Al5O12 (YAG) phosphors in the powder form was successfully synthesized by multiple-step solid-state reaction under the reducing Ar:5%H2 atmosphere. Their physical properties were investigated by means of X-ray diffraction, time-resolved luminescence spectroscopy, and electron paramagnetic resonance (EPR). Special attention was given to well-grounded confirmation of Eu2+ occurrence in the YAG structure. X-ray diffraction confirmed the presence of a major YAG phase in all samples. The influence of Eu concentration, form of doping (EuS, EuF2, or Eu2O3) and number/form of annealing steps was studied. Corresponding characteristics were measured and evaluated in a broad temper…
Oxygen influence on luminescence properties of rare-earth doped NaLaF 4
2016
Abstract Luminescence properties of erbium and europium doped NaLaF4 with different oxygen content have been studied. Vacuum ultraviolet (VUV) excitation luminescence spectroscopy technique has been applied by using synchrotron radiation excitation. It was found that oxygen impurity leads to significant degradation of Er3+ or Eu3+ emission under VUV excitation. The intensive O2−–Er3+ charge transfer excitation band has been detected from oxygen abundant NaLaF4 in the 150–165 nm spectral range. This band reveals a competing absorption mechanism in oxygen containing NaLaF4. It is clearly demonstrated that one reason for the Er3+ emission degradation in oxygen abundant NaLaF4 is strong suppres…