0000000000115571
AUTHOR
José ÁNgel García
Recombination processes in unintentionally doped GaTe single crystals
Emission spectra of GaTe single crystals in the range of 1.90–1.38 eV have been analyzed at different temperatures and excitation intensities by photoluminescence, photoluminescence excitation, and selective photoluminescence. A decrease in band gap energy with an increase in temperature was obtained from the redshift of the free exciton recombination peak. The energy of longitudinal optical phonons was found to be 14±1 meV. A value of 1.796±0.001 eV for the band gap at 10 K was determined, and the bound exciton energy was found to be 18±0.3 meV. The activation energy of the thermal quenching of the main recombination peaks and of the ones relating to the ionization energy of impurities and…
Re-evaluation of moisture sources for the August 2002 extreme rainfall episode in central Europe: Evaporation from falling precipitation included in a mesoscale modeling system
Summary Discriminating moisture sources with precision is an important requirement to better understand the processes involved in extreme rainfall episodes. In a previous contribution by Gangoiti et al. (2011b), an innovative technique was presented to assess surface moisture sources contributing to a target precipitation within a Lagrangian framework. The technique was based in transporting parcels of vapor, representing the target precipitation, across a set of nested grids covering a large area at different resolutions. A mesoscale model estimated the meteorological variables to transport and redistribute the vapor back into its original sources, all of them assumed to be at the surface.…
Photoluminescence study of radiative transitions in ZnTe bulk crystals
Abstract This paper focuses on photoluminescence (PL) and selective photoluminescence (SPL) of ZnTe bulk crystals grown by the cold traveling heater method. The crystals exhibit a PL response with a much more intense excitonic zone than the one due to free-to-bound and donor–acceptor bands, denoting a good sample quality. In particular, we have investigated the Y 1 and Y 2 peaks which, in epitaxial layers, have usually been associated with structural defects. On bulk samples they have not been detected so far because of different masked mechanisms. SPL measurements show that the electrons are the most likely involved carriers for this emission. Additionally, the analysis of the PL variation…
Correlation between Zn vacancies and photoluminescence emission in ZnO films.
Photoluminescence and positron annihilation spectroscopy have been used to characterize and identify vacancy-type defects produced in ZnO films grown on sapphire by metal-organic chemical-vapor deposition. The photoluminescence of the samples in the near band edge region has been studied, paying particular attention to the emission at 370.5 nm (3.346 eV). This emission has been correlated to the concentration of Zn vacancies in the films, which has been determined by positron annihilation spectroscopy. Jesus.Zuniga@uv.es Vicente.Munoz@uv.es
Near band edge recombination mechanisms in GaTe
GaTe samples of p-type have been investigated by analyzing the photoluminescence (PL) response for different excitation intensities at energies higher than the band gap. The PL intensity variation of recombination peaks as a function of the excitation intensity has been measured and fitted by a power law. The results show some particular features that do not appear in other III-V and II-VI compound semiconductors. These features can be interpreted by means of the recombination dynamics of the carriers in the band-gap edges. The expressions for the coefficients associated with different recombination rates and the relations between them are derived and used for understanding the recombinatio…
Cathodoluminescence and photoluminescence study of plastically deformed ZnTe bulk single crystals
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.
Interpenetrated Luminescent Metal-Organic Frameworks based on 1H-Indazole-5-carboxylic Acid
Herein we report the formation and characterization of two novel Zn-based multifunctional metal-organic frameworks (MOFs) based on 1H-indazole-5-carboxylic acid and bipyridine-like linkers, synthesized by soft solvothermal routes. These materials possess isoreticular 2-fold interpenetrated three-dimensional structures that afford a flexible character and allow porosity modulation of the MOFs as confirmed by CO2 sorption measurements. Apart from this attractive structural feature, the MOFs exhibit fascinating luminescent properties involving both luminescence thermometry and long-lasting phosphorescence.
Temperature- and illumination-induced charge-state change in divacancies of GaTe
Temperature-dependent positron annihilation lifetime spectroscopy measurements have been performed in GaTe samples, with and without illumination. The average lifetime shows a monotonous temperature evolution but the lifetime decomposition shows a rich behavior. It is produced by two types of vacancy defects. The vacancy-type defects characterized by their shorter lifetime change their charge state below 100 K and when illuminating with light of an energy of 0.8 eV.
Effect of plastic deformation on photoluminescence of ZnTe bulk monocrystals
Abstract In this work ZnTe bulk single crystals have been deformed by axial compression with the aim of analyzing the luminescence properties related to intrinsic structural defects like dislocations. Plastic deformation greatly decreases the overall PL response, near-band-edge luminescence as well as deep level-related emissions. Results indicate a close relationship between the so-called Y1 and Y2 bands and the density of generated dislocations. Plastic deformation also produces an emission band at 603 nm whose intensity is proportional to the amount of introduced deformation.
Influence of thermally induced structural transformations on the magnetic and luminescence properties of tartrate-based chiral lanthanide organic-frameworks
This work reports on the synthesis and characterization of five enantiomeric pairs of isostructural 3D metal-organic frameworks (MOFs) with the general formula {[Ln2(μ4-tar)2(μ-tar)(H2O)2]·xH2O}n [where Ln(iii) = Tb (Tb-L and Tb-D), Dy (Dy-L and Dy-D), Ho (Ho-L and Ho-D), Er (Er-L and Er-D) and Tm (Tm-L and Tm-D); tar = tartrate (d- or l-) and x = 3 or 4 depending on the counterpart], which possess interesting luminescence and magnetic properties. These MOFs undergo progressive and reversible dehydration processes upon controlled heating yielding three crystalline phases (Ln-L′, Ln-L′′ and Ln-L′′′). Alternating current magnetic measurements on Tb, Dy and Er-based compounds exhibit field ind…
Deep center luminescence versus surface preparation of ZnSe single crystals
A close relationship between the photoluminescence emissions labeled Y and S, related to dislocations and extended structural defects, and the preparation of the surface state of ZnSe single crystals before PL (photoluminescence) measurements has been established. The samples were obtained by solid-phase recrystallization under different pressure conditions. An easy method for achieving good quality surfaces with a very significant reduction of such Y and S PL emissions is proposed.
Observation of a charge delocalization from Se vacancies inBi2Se3: A positron annihilation study of native defects
By means of positron annihilation lifetime spectroscopy, we have investigated the native defects present in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, which belongs to the family of topological insulators. We experimentally demonstrate that selenium vacancy defects $({\text{V}}_{\text{Se1}})$ are present in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ as-grown samples, and that their charge is delocalized as temperature increases. At least from 100 K up to room temperature both ${\text{V}}_{\text{Se1}}^{0}$ and ${\text{V}}_{\text{Se1}}^{+}$ charge states coexist. The observed charge delocalization determines the contribution of ${\text{V}}_{\text{Se1}}$ defects to the $n$-type conductivity of ${\mathrm{…
Annealing-induced Changes in the Electronic and Structural Properties of ZnTe Substrates
The aim of this study is to demonstrate that the electronic and structural properties of II–VI substrates, here ZnTe, can be dramatically affected by thermal heating at temperatures in the range of those typically used in the epitaxial metalorganic chemical vapor deposition processes. Photoluminescence response shows that annealing at these temperatures produces a reduction of the sample crystalline quality, decreasing the free exciton emission relative to the deep level related one. Some factors, like the change in the charge and stress state of dislocations, Cu diffusion, and oxygen incorporation, could be responsible for changes in the substrate properties, which can produce stresses and…
Determination of defect content and defect profile in semiconductor heterostructures
In this article we present an overview of the technique to obtain the defects depth profile and width of a deposited layer and multilayer based on positron annihilation spectroscopy. In particular we apply the method to ZnO and ZnO/ZnCdO layers deposited on sapphire substrates. After introducing some terminology we first calculate the trend that the W/S parameters of the Doppler broadening measurements must follow, both in a qualitative and quantitative way. From this point we extend the results to calculate the width and defect profiles in deposited layer samples.