Search results for "Exciton"
showing 10 items of 317 documents
Inhibition of light emission from the metastable tetragonal phase at low temperatures in island-like films of lead iodide perovskites
2019
Photonic applications based on halide perovskites, namely CH3NH3PbI3 (MAPbI3), have recently attracted remarkable attention due to the high efficiencies reported for photovoltaic and light emitting devices. Despite these outstanding results, there are many temperature-, laser excitation power-, and morphology-dependent phenomena that require further research to be completely understood. In this work, we have investigated in detail the nature of exciton optical transitions and recombination dynamics below and above the orthorhombic/tetragonal ('O'-/'T'-) temperature phase transition (∼150 K) depending on the material continuity (continuous-like) or discontinuity (island-like) in MAPbI3 films…
<title>Localized excitons in fluoroperovskite LiBaF<formula><inf><roman>3</roman></inf></formula> crystals&…
2003
Two radiating processes in LiBaF3 crystals, fast valence-core transitions (5.4 - 6.5 eV) and slow, so called self-trapped exciton luminescence (about 4.3 eV), are important for practical application. Here we present a study of 4.3 eV luminescence under X-ray excitation and photoexcitation as well as under photostimulation after X-irradiation of undoped and Ag-doped LiBaF3 crystals at various temperatures. It is shown that 4.3 eV luminescence appears under X-ray excitation at least from 85 K to 400 K in both undoped and doped crystals. In all samples studied the excitation spectra of 4.3 eV luminescence contain both the main exciton like band at the edge of fundamental absorption at about 10…
Controlling the oxidation processes of Zn nanoparticles produced by pulsed laser ablation in aqueous solution
2016
We used online UV-VIS optical absorption and photoluminescence spectra, acquired during and after pulsed laser ablation of a Zinc plate in aqueous solution, to investigate the effect of the laser repetition rate and liquid environment on the oxidation processes of the produced nanoparticles. A transient Zn/ZnO core-shell structure was revealed by the coexistence of an absorption peak around 5.0 eV due to Zn surface plasmon resonance and of an edge at 3.4 eV coming from wurtzite ZnO. The growth kinetics of ZnO at the various repetition rates, selectively probed by the excitonic emission at 3.3 eV, began immediately at the onset of laser ablation and was largely independent of the repetition …
Radiative phonon-assisted and Auger recombination in Si nanocrystals
2010
Abstract Recent analysis of the literature shows that the photoluminescence (PL) of Si nanocrystals and porous silicon is caused by phonon-assisted exciton radiative recombination, as well as by direct radiative electron transfer from the second to the first conduction sub-band, which is related to the Auger recombination. The PL decay curve for porous silicon after excitation with ultraviolet laser pulse has been established experimentally. We have constructed continuity equations for the first and the second conduction sub-bands, including radiative phonon-assisted exciton recombination, Auger recombination and direct radiative transition from the second to the first conduction sub-band. …
Single-molecule spectroscopy of molecular aggregates at low temperature
2004
We have conducted single-molecule spectroscopy of a fluorescent polyphenylene dendrimer consisting of four peripheral perylenemonoimides which serve as energy donors and a central terrylenediimide which is the energy acceptor. After selective excitation of the donors the low-temperature emission spectra of single dendrimers show the purely electronic zero-phonon line as the most prominent feature of the acceptor. These sharp emission lines are subjected to appreciable spectral shifts. Fluorescence excitation spectroscopy of individual dendrimers in the spectral region of the donor absorption allows to extract energy transfer rates for single donors within the dendrimer. Although the energy …
Short-lived luminescence of mixed silver halides
1993
Abstract Two kinds of excitonic luminescence were investigated for the entire series of solid solutions, AgBr1−xClx, (0 ⪕ x ⪕ 1). The time-resolved spectra observed around 2.5 eV after both pulsed high-power electron beam and N2-laser irradiations are analyzed in terms of the diffusion-controlled recombination of Frenkel defects Ag0i and Ag2+V-c. It is shown that the effective activation energy of Ag0i migration is a linear function of the composition x; and predominantly two kinds of nearest neighbours contribute to this process. The position of maximum of the excitonic molecule luminescence found in mixed monocrystals and fibers reveals a distinctive dependence on the composition x. Its a…
Mechanism for energy transfer processes between Ce3+ and Tb3+ in LaPO4:Ce,Tb nanocrystals by time-resolved luminescence spectroscopy
2010
The energy transfer mechanisms between Ce 3+ and Tb 3+ in LaPO 4 :Ce,Tb nanocrystals have been studied by means of time-resolved luminescence spectroscopy in a wide temperature range (10-300K). Special attention was paid to detailed comparative analysis of both rise and decay emission components of both Ce 3+ and Tb 3+ . Surprisingly, a relatively slow rise (several microseconds) of Tb 3+ emission under 266-nm laser excitation was detected, which corresponds to the 4f-5d transition of Ce 3+ in LaPO 4 . It was shown that this rise of Tb 3+ emission could not have arisen due to relaxation of Ce 3+ ions, whose excited state has a lifetime of about 20ns. It was demonstrated that the generally a…
Energy of excitons and acceptor–exciton complexes to explain the origin of ultraviolet photoluminescence in ZnO quantum dots embedded in a SiO2 matrix
2011
Abstract Assuming finite depth and within the effective mass approximation, the energies of exciton states and of the acceptor–exciton complexes confined in spherical ZnO quantum dots (QDs) embedded in a SiO2 matrix are calculated using a matrix procedure, including a three-dimensional confinement of carrier in the QDs. This theoretical model has been designed to illustrate the two emission bands in the UV region observed in our experimental Photoluminescence spectrum (PL), with the first emission band observed at 3.04 eV and attributed to the bound ionized acceptor–exciton complexes, and the second one located at 3.5 and assigned to the free exciton. Our calculations have revealed a good a…
High pressure and high magnetic field behaviour of free and donor-bound-exciton photoluminescence in InSe
2009
We report here first magneto-photoluminescence investigations under high pressure up to 6 GPa on III-VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap opening driven by Landau quantization became observable by using a 60 T pulsed magnet. The pressure-induced enhancement of the diamagnetic coefficient is consistent with the increase of the dielectric constant under pressure while the evolution of the linear coefficient is consistent with a slight increase of the electron effective mass up to 4 GPa and a direct-to-indirect conduction-band crossover around that pressure.
Excitonic Transitions in Homoepitaxial GaN
2001
The photoluminescence spectrum of a high quality homoepitaxial GaN film has been measured as a function of temperature. As temperature increases the recombination of free excitons dominates the spectra. Their energy shift has successfully fitted in that temperature range by means of the Bose-Einstein expression instead of Varshni's relationship. Values for the parameters of both semi-empirical relations describing the energy shift are reported and compared with the literature.