Search

The lifetimes of a series of N-related photoluminescence lines (A2–A6) in GaAs1-xNx (x=0.1%) were studied under hydrostatic pressures at ∼30 K. The lifetimes of A5 and A6 were found to increase rapidly with increasing pressure: from 2.1 ns at 0 GPa to more than 20 ns at 0.92 GPa for A5 and from 3.2 ns at 0.63 GPa to 10.8 ns at 0.92 GPa for A6. The lifetime is found to be closely correlated with the binding energy of the N impurity states, which is shown either in the pressure dependence for a given emission line or in the lifetime variation from A2 to A6. [ABSTRACT FROM AUTHOR]

We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at ∼40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd/A and 8.8 lm/W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component. [ABSTRACT FROM AUTHOR]

The nature of the ∼370-nm (3.35-eV) photoluminescence (PL) in Si oxide and nanostructures, which has a PL excitation band at ∼260 nm, is studied experimentally and theoretically. It is revealed that the PL occurs at the interface between Si structure and its oxide and is closely associated with a characteristic infrared absorption band at ∼1250 cm-1. Spectral analyses suggest that the ∼370-nm PL originates in the –SiO3 group, which bonds to Si structural surface. The density functional theory calculations are consistent with our experiments. This work clarifies some controversies regarding the ∼370-nm PL mechanisms in a number of Si oxide and nanostructures. [ABSTRACT FROM AUTHOR]

Exciton localization in Te-rich ZnSTe epilayers has been studied by photoluminescence (PL) and time-resolved PL. The sulfur-related exciton emission is found to dominate the radiative recombination at low temperature and is shifted to the low energy with the increase of S concentration. By measuring the PL dependence on temperature and by analyzing the PL decay process, we have clarified the localization nature of the sulfur-related exciton emission. Furthermore, the difference of the localization effect in Te- and S-rich ZnSTe is also compared and discussed. [ABSTRACT FROM AUTHOR]

The recombination kinetics of Te isoelectronic centers in ZnS1-xTex (0.0065≤x≤0.85) alloys is studied by time-resolved photoluminescence (TRPL) at low temperature. The measured radiative recombination lifetimes of different Te bound exciton states are quite different, varying from a few nanoseconds to tens of nanosecond. As the bound exciton state evolves from a single Te impurity (Te1) to larger Te clusters (Ten,n=2,3,4), the recombination lifetime increases. It reaches maximum (∼40 ns) for the Te4 bound states at x=0.155. The increase of the exciton lifetime is attributed to the increasing exciton localization effect caused by larger localization potential. In the large Te composition range (x>0.155), the exciton recombination lifetime decreases monotonically with Te composition. It is mainly due to the hybridization between the Te localized states and the host valence band states. The composition dependences of the exciton binding energy and the photoluminescence (PL) line width show the similar tendency that further support the localization picture obtained from the TRPL measurement. [ABSTRACT FROM AUTHOR]

We have investigated the formation mechanism of the interfacial electric field in LiNbO3(or LiTaO3)/α-sapphire crystal structures, which is important in understanding the photoluminescence properties of this kind of ferroelectric film-coated crystal material. It is revealed that the interfacial electric field arises from the interfacial polarization charge generated during poling of LiNbO3(or LiTaO3) film near Curie temperature, which induces forced polarization of the α-sapphire crystal. As a result, lattice distortions of the α-sapphire crystal change the crystal field of Cr3+ ion in the sapphire crystal and therefore lead to intensity enhancement of R-line luminescence from Cr3+ centers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

SiO[SUB2]/LiNbO[SUB3](LN)/SiO[SUB2] sandwich structures were fabricated for exploring efficient light emission. After annealing at 1000 °C in O[SUB2] for 30 min, this kind of sandwich structure shows a strong ultraviolet photoluminescence (PL) with an asymmetric spectral shape. This PL spectrum may be Gaussian divided into two bands peaked at 310 (α-band) and 346 nm (β-band). If the layer of LN film is replaced by an Fe-doped LN (LN:Fe) one, the β-band vanishes and the α-band redshifts. The α-band is greatly enhanced and simultaneously becomes asymmetrical after this kind of SiO[SUB2]/LN:Fe/SiO[SUB2] structure is annealed for 60 min. Spectral analysis suggests that the α-band arises from an optical transition in positively charged E8 centers at the interfaces between the LN(:Fe) film and the two SiO[SUB2] layers, while the β-band arises from intrinsic defects in the LN(:Fe) films. The mechanism for the PL enhancement is discussed in terms of a photorefractive effect in the LN(:Fe) films. [ABSTRACT FROM AUTHOR]

The influence of nonradiative recombination on the photoluminescence (PL) decay dynamics in GaInNAs/GaAs quantum wells is studied by time-resolved photoluminescence under various excitation intensities. It is found that the PL decay process strongly depends on the excitation intensity. In particular, under the moderate excitation levels the PL decay curves exhibit unusual nonexponential behavior and show a convex shape. By introducing a new parameter of the effective concentration of nonradiative recombination centers into a rate equation, the observed results are well simulated. The cw PL data further demonstrate the nonradiative recombination effect on the optical properties of GaInNAs/GaAs quantum wells. [ABSTRACT FROM AUTHOR]

Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488 nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325 nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures. [ABSTRACT FROM AUTHOR]

Starting from the growth of high-quality 1.3 μm GaInNAs/GaAs quantum well (QW), the QW emission wavelength has been extended up to 1.55 μm by a combination of lowering growth rate, using GaNAs barriers and incorporating some amount of Sb. The photoluminescence properties of 1.5 μm range GaInNAsSb/GaNAs QWs are quite comparable to the 1.3 μm QWs, revealing positive effect of Sb on improving the optical quality of the QWs. A 1.59 μm lasing of a GaInNAsSb/GaNAs single-QW laser diode is obtained under continuous current injection at room temperature. The threshold current density is 2.6 kA/cm2 with as-cleaved facet mirrors. [ABSTRACT FROM AUTHOR]

Quasi-aligned ZnO nanotubes have been grown on silicon substrates by metalorganic chemical vapor deposition without using any catalyst. Two kinds of ZnO nanotubular structures were found: Nanotubes with single walls and nanotubes with double walls. The nanotubes were grown along the [001] direction. Room-temperature photoluminescence measurements of the ZnO nanotubes indicate strong ultraviolet emission and weak green emission. A new growth mode for these ZnO nanotubes is proposed, which can be used to prepare other nanotubular structures. [ABSTRACT FROM AUTHOR]

Coupled three-dimensional GeSi quantum dot crystals (QDCs) are realized by multilayer growth of quantum dots (QDs) on patterned SOI (001) substrates. Photoluminescence spectra of these QDCs show non-phonon (NP) recombination and its transverse-optical (TO) phonon replica of excitons in QDs. With increasing excitation power, peak energies of both the NP and TO peaks remain nearly constant and the width of the TO peak decreases. These anomalous features of the PL peaks are attributed to miniband formation due to strong coupling of the holes and the emergence of quasioptical phonon modes due to periodic scatters in ordered GeSi QDs. [ABSTRACT FROM AUTHOR]