Search results for "Exciton"
showing 10 items of 317 documents
Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots
2012
We have investigated the temperature dependent recombination dynamics in two bimodally distributed InAs self assembled quantum dots samples. A rate equations model has been implemented to investigate the thermally activated carrier escape mechanism which changes from exciton-like to uncorrelated electron and hole pairs as the quantum dot size varies. For the smaller dots, we find a hot exciton thermal escape process. We evaluated the thermal transfer process between quantum dots by the quantum dot density and carrier escape properties of both samples. © 2012 American Institute of Physics.
Time‐resolved absorption and luminescence following electron‐hole pair creation in ZnO
2008
We report transient absorption induced by electron-hole excitation in undoped ZnO. A laser pump/continuum probe method covers 2–300 ps, and an electron pulse with lamp transmission covers 8–300 ns. The broad absorption spectrum increases monotonically with wavelength from 900 to 1600 nm. Following a reasonable hypothesis that the free-carrier-like induced infrared absorption is proportional to the total number of free carriers, excitons, and shallow-trapped carriers in the sample, these data allow setting an upper limit on the quantum efficiency of a specified lifetime component of luminescence. For the undoped commercial ZnO studied in this report, the quantum efficiency of room temperatur…
Energy transfer from colour centres to the dopant in alkali halides
1997
Abstract Energy transfer from F centres to the dopant ions in photostimulated processes is examined. It was found that in alkali halide systems the radiation defects are disposed in near vicinity of the dopants. Recombination of defects also takes place to a limited extent near the dopant with a fast and high-yield energy transfer to the latter. Role of unrelaxed H centres in the formation of donor-acceptor pairs is discussed. Some special exciton energy transfer mechanisms are analysed as well.
Residual strain effects on the two-dimensional electron gas concentration of AlGaN/GaN heterostructures
2001
Ga-face AlGaN/GaN heterostructures with different sheet carrier concentrations have been studied by photoluminescence and Raman spectroscopy. Compared to bulk GaN, an energy shift of the excitonic emission lines towards higher energies was observed, indicating the presence of residual compressive strain in the GaN layer. This strain was confirmed by the shift of the E2 Raman line, from which biaxial compressive stresses ranging between 0.34 and 1.7 GPa were deduced. The spontaneous and piezoelectric polarizations for each layer of the heterostructures have been also calculated. The analysis of these quantities clarified the influence of the residual stress on the sheet electron concentratio…
Transport properties of nitrogen doped p‐gallium selenide single crystals
1996
Nitrogen doped gallium selenide single crystals are studied through Hall effect and photoluminescence measurements in the temperature ranges from 150 to 700 K and from 30 to 45 K, respectively. The doping effect of nitrogen is established and room temperature resistivities as low as 20 Ω cm are measured. The temperature dependence of the hole concentration can be explained through a single acceptor‐single donor model, the acceptor ionization energy being 210 meV, with a very low compensation rate. The high quality of nitrogen doped GaSe single crystals is confirmed by photoluminescence spectra exhibiting only exciton related peaks. Two phonon scattering mechanisms must be considered in orde…
Luminescence and electron transport properties of GaN and AlN layers
2001
Abstract The transport properties of free charge carriers, photo- and cathodo-luminescence (CV) in GaN and AlN films obtained by MOCVD technique on sapphire and Si substrates, are investigated. The concentration of free charge carriers in GaN is of order 10 17 – 10 19 cm −3 whereas AlN thin films are insulating. The Hall mobility of electrons are 80– 140 cm 2 / V s ). In undoped GaN films the spectral composition of CL is close to photoluminescence (PL) when excited in the region of band–band transitions. The decay time constant of the 3.44 eV UV emission attributed to the bound exciton is considerably less than 1 ns , whereas the 3.26 eV violet (VI) band shows a slow hyperbolical decay ove…
Photoconductivity & photoelectron emission of LiGaO2 crystal excited in intrinsic absorption range
2019
This research is funded by the Latvian Council of Science, project “Research of luminescence mechanisms and dosimeter properties in prospective nitrides and oxides using TL and OSL methods], project No. lzp-2018/0361.
New Quasi-Atomic Nanoheterostructures: Superatoms and Excitonic Quasi-Molecules
2016
In this review, the state-of-the-art of research of artificial atoms (superatoms or quasi-atomic nanoheterostructures) and more complex nanostructures based on them—synthetic molecules is discussed, a new model of an artificial atom, which satisfactorily explains its electronic properties, is proposed, and the prospects for development of the new scientific trend are mentioned. В этом обзоре обсуждается современное состояние исследований искусственных атомов (сверхатомов или квазиатомных наногетероструктур) и более сложных наноструктур на их основе — синтетических молекул, предложена новая модель искусственного атома, удовлетворительно объясняющая его электронные свойства, а также указаны п…
Colloidal Nanoplatelet/Conducting Polymer Hybrids: Excitonic And Material Properties
2016
WOS:000370678700053 Here we present the first account of conductive polymer/colloidal nanoplatelet hybrids. For this, we developed DEH-PPV-based polymers with two different anchor groups (sulfide and amine) acting as surfactants for CdSe nanoplatelets, which are atomically flat semiconductor nanocrystals. Hybridization of the polymers with the nanoplatelets in the solution phase was observed to cause strong photoluminescence quenching in both materials. Through steady-state photoluminescence and excitation spectrum measurements, photoluminescence quenching was shown to result from dominant exciton dissociation through charge transfer at the polymer/nanoplatelet interfaces that possess a sta…
The photophysics and photochemistry of cofacial free base and metallated bisporphyrins held together by covalent architectures
2007
Abstract This review focuses on the photophysical properties of bisporphyrin systems held in a face-to-face configuration by covalent bonds via flexible or rigid spacers and metal–metal bonds. The cofacial arrangement induces intramolecular bismacrocycle interactions promoting basic photophysical events such as excitonic interactions and energy and electron transfers. These events are relevant to mimic light harvesting and reactor devices known for photosynthesis in plants, and can be monitored by luminescence and flash photolysis methods.