Phosphorescence of CdS nanoparticles in polymer matrix as an indication of host-guest interaction

We report on the observation of the long-lasting low-temperature photoluminescence decay in the hybrid system nano-CdS/polyvinyl alcohol with a characteristic time of about 1.7 s. The origin of the phosphorescence is ascribed to the accumulation of photo-excited excitons in the traps within the polymeric matrix with subsequent transfer of the excitation to the embedded CdS nanoparticles

Effects of Ultraviolet Light on Optical Properties of Colloidal CdS Nanoparticles Embedded in Polyvinyl Alcohol (PVA) Matrix

CdS nanoparticles have been synthesized in aqueous solution using polyvinyl alcohol (PVA) as a capping reagent. The effects of exposure by ultraviolet (UV) light on optical properties of nanocomposites consisting of colloidal CdS nanoparticles and a polymer PVA matrix were studied by employing photoluminescence (PL) spectroscopy. It is shown that UV-induced changes of the photoluminescence intensity in PVA are caused by creation and healing of non-radiative recombination centers. It is also concluded that in the nanocomposites, the UV-induced changes of the PL intensity are predominantly governed by processes at the NP/PVA interfaceFinancial support from the Swedish Institute via Visby program is greatly appreciated

Role of the host polymer matrix in light emission processes in nano-CdS/poly vinyl alcohol composite

Participation of a polymericmedia in light-emitting processes of composite nano-CdS/polyvinyl alcohol is studied by probing different absorption-emission routes via adjustment of excitation wavelengths. It is shown that the polymeric constituent of the composite contributes chiefly to the photoluminescence excitation processes via absorption and excitation transfer to the embedded CdS nanoparticles while the composite emission occurs mostly within the nanoparticles.Financial support from the Swedish Institute via Visby program is greatly appreciated

Telecommunication wavelength GaAsBi light emitting diodes

GaAsBi light emitting diodes containing ∼6% Bi are grown on GaAs substrates. Good room-temperature electroluminescence spectra are obtained at current densities as low as 8 Acm − 2. Measurements of the integrated emitted luminescence suggest that there is a continuum of localised Bi states extending up to 75 meV into the bandgap, which is in good agreement with previous photoluminescence studies. X-ray diffraction analysis shows that strain relaxation has probably occurred in the thicker samples grown in this study

Identification of point defects in Ga(Al)NAs alloys

By employing the optically detected magnetic resonance (ODMR) technique, two different Ga(ind i) defects, namely Ga(ind i)-A and Ga(ind i)-B, are found and identified in the investigated Ga(Al)NAs epilayers grown on GaAs substrates by molecular-beam epitaxy (MBE). This finding shows that Ga interstitials are common intrinsic defects in various dilute nitrides. In addition to the Ga(ind i)-related defects, "middle line" ODMR signals were observed at around g=2 and are suggested to arise from superposition of a defect with a single ODMR line and a defect with an unresolved HF structure. All defects studied are shown to act as non-radiative recombination centers, and are therefore harmful to performance of potential light-emitting devices based on the alloys

Room temperature spin filtering effect in GaNAs: Role of hydrogen

Effects of hydrogen on the recently discovered defect-engineered spin filtering in GaNAs are investigated by optical spin orientation and optically detected magnetic resonance. Post-growth hydrogen treatments are shown to lead to nearly complete quenching of the room-temperature spin-filtering effect in both GaNAs epilayers and GaNAs/GaAs multiple quantum wells, accompanied by a reduction in concentrations of Gai interstitial defects. Our finding provides strong evidence for efficient hydrogen passivation of these spin-filtering defects, likely via formation of complexes between Gai defects and hydrogen, as being responsible for the observed strong suppression of the spin-filtering effect after the hydrogen treatments. © 2011 American Institute of Physics

Effect of postgrowth hydrogen treatment on defects in GaNP

Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment (<= 100 eV H ions). Among them, two defect complexes are identified to contain a Ga interstitial. Possible mechanisms for the H-induced defect activation and creation are discussed. Carrier recombination via these defects is shown to efficiently compete with the near band-edge PL, explaining the observed degraded optical quality of the alloys after the H treatment. (C) 2011 American Institute of Physics. [doi:10.1063/1.3576920

Efficient room-temperature nuclear spin hyperpolarization of a defect atom in a semiconductor

Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (~150 Gauss) and nuclear spin polarization (~15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in &lt;5 μs at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications

Molecular beam epitaxial growth of GaAs/GaNAsBi core–multishell nanowires

GaAs/GaNAsBi/GaAs core–multishell nanowires were grown using molecular beam epitaxy on Si(111) substrates. The formation of the 20 nm wide GaNAsBi shell with a regular hexagonal structure was observed. The shell is estimated to contain approximately 1.5% N and 2.6% Bi and has a compressive lattice mismatch of less than 0.2% with GaAs layers. The strain mediation by the introduction of both N and Bi suppresses the crystalline deformation, resulting in the clear formation of the GaNAsBi shell. Thus, we obtained room-temperature photoluminescence with the maximum position at approximately 1300 nm from the GaAs/GaNAsBi/GaAs core–multishell nanowires