Biexciton Blinking in CdSe-Based Quantum Dots

Experiments on single colloidal quantum dots (QDs) have revealed temporal fluctuations in the emission efficiency of the single-exciton state. These fluctuations, often termed “blinking”, are caused by opening/closing of charge-carrier traps and/or charging/discharging of the QD. In the regime of strong optical excitation, multiexciton states are formed. The emission efficiencies of multiexcitons are lower because of Auger processes, but a quantitative characterization is challenging. Here, we quantify fluctuations of the biexciton efficiency for single CdSe/CdS/ZnS core-shell QDs. We find that the biexciton efficiency “blinks” significantly. The additional electron due to charging of a QD accelerates Auger recombination by a factor of 2 compared to the neutral biexciton, while opening/closing of a charge-carrier trap leads to an increase of the nonradiative recombination rate by a factor of 4. To understand the fast rate of trap-assisted recombination, we propose a revised model for trap-assisted recombination based on reversible trapping. Finally, we discuss the implications of biexciton blinking for lasing applications

Constraints on the evolution of Taranaki Fault from thermochronology and basin analysis: Implications for the Taranaki Fault play

Taranaki Fault is the major structure defining the eastern margin of Taranaki Basin and marks the juxtaposition of basement with the Late Cretaceous-Paleogene succession in the basin. Although the timing of the basement over-thrusting on Taranaki Fault and subsequent marine onlap on to the basement block are well constrained as having occurred during the Early Miocene, the age of formation of this major structure, its character, displacement history and associated regional vertical movement during the Late Cretaceous- Recent are otherwise poorly known. Here we have applied (i) apatite fission track thermochronology to Mesozoic basement encountered in exploration holes and in outcrop to constrain the amount and timing of Late Cretaceous-Eocene exhumation of the eastern side of the fault, (ii) basin analysis of the Oligocene and Miocene succession east of the fault to establish the late-Early Miocene - Early Pliocene subsidence history, and (iii), regional porosity-bulk density trends in Neogene mudstone to establish the late uplift and tilting of eastern Taranaki Basin margin, which may have been associated with the main period of charge of the underlying Taranaki Fault play. We make the following conclusions that may be useful in assessing the viability of the Taranaki Fault play. (1) Mid-Cretaceous Taniwha Formation, intersected in Te Ranga-1 was formerly extensive across the western half of the Kawhia Syncline between Port Waikato and Awakino. (2) Taranaki Fault first formed as a normalfault during the Late Cretaceous around 85±10 Ma, and formed the eastern boundary of the Taranaki Rift-Transform basin. (3) Manganui Fault, located onshore north of Awakino, formed as a steeply east dipping reverse fault and accommodated about four km of displacement during the mid-Cretaceous. (4) Uplift and erosion, involving inversion of Early Oligocene deposits, occurred along the Herangi High during the Late Oligocene. This may have been associated with initial reverse movement on Taranaki Fault. (5) During the Early Miocene (Otaian Stage) the Taranaki and Manganui Faults accommodated the westward transport of Murihiku basement into the eastern margin of Taranaki Basin, but the amount of topography generated over the Herangi High can only have been a few hundred metres in elevation. (6) The Altonian (19-16 Ma) marked the start of the collapse of the eastern margin of Taranaki Basin that lead during the Middle Miocene to the eastward retrogradation of the continental margin wedge into the King Country region. During the Late Miocene, from about 11 Ma, a thick shelf-slope continental margin wedge prograded northward into the King Country region and infilled it (Mt Messenger, Urenui, Kiore and Matemateaonga Formations). (7) During the Pliocene and Pleistocene the whole of central New Zealand, including the eastern margin of Taranaki Basin, became involved in long wavelength up-doming with 1-2 km erosion of much of the Neogene succession in the King Country region. This regionally elevated the Taranaki Fault play into which hydrocarbons may have migrated from the Northern Graben region

Megasequence architecture of Taranaki, Wanganui, and King Country basins and Neogene progradation of two continental margin wedges across western New Zealand.

Taranaki, Wanganui and King Country basins (formerly North Wanganui Basin) have been regarded as discrete basins, but they contain a very similar Neogene sedimentary succession and much of their geological history is held in common. Analysis of the stratigraphic architecture of the fill of each basin reveals the occurrence of four 2nd order megasequences of tectonic origin. The oldest is the early-early Miocene (Otaian Stage) Mahoenui Group/megasequence, followed by the late-early Miocene (Altonian Stage) Mokau Group/megasequence (King Country Basin), both of which correspond to the lower part of the Manganui Formation in Taranaki Basin. The third is the middle to late Miocene Whangamomona Group/megasequence, and the fourth is the latest Miocene-Pleistocene Rangitikei Supergroup/megasequence, both represented in the three basins. Higher order sequences (4th, 5th, 6th), having a eustatic origin, are evident in the Whangamomona and Rangitikei megasequences, particularly those of 5th order with 41 ka periodicity. The distribution of the megasequences are shown in a series of cross-section panels built-up from well -to-well correlations, complemented by time-stratigraphic cross-sections. The base of each megasequence is marked by marine flooding and represents a discrete phase in basin development. For the first megasequence this corresponded to rapid subsidence of the King Country Basin in a compressional setting and basement overthrusting on the Taranaki Fault, with the rapid introduction of terrigenous sediment during transgression. The Mahoenui megasequence accumulated mostly at bathyal depths; no regressive deposits are evident, having been eroded during subsequent uplift. The second (Mokau) megasequence accumulated during reverse movement on the Ohura Fault, formation of the Tarata Thrust Zone, and onlap of the basement block between the Taranaki Fault and the Patea-Tongaporutu-Herangi High (PTH). The Whangamomona megasequence accumulated during extensive reflooding of King Country Basin, onlap of the PTH High and of basement in the Wanganui Basin. This is an assymetrical sequence with a thin transgressive part (Otunui Formation) and a thick regressive part (Mount Messenger to Matemateaonga Formations). It represents the northward progradation of a continental margin wedge with bottom-set, slope-set and top-set components through Wanganui and King Country basins, with minor progradation over the PTH High and into Taranaki Basin. The Rangitikei megasequence is marked by extensive flooding at its base (Tangahoe Mudstone) and reflects the pull-down of the main Wanganui Basin depocentre. This megasequence comprises a second progradational margin wedge, which migrated on two fronts, one northward through Wanganui Basin and into King Country Basin, and a second west of the PTH High, through the Toru Trough and into the Central and Northern Grabens of Taranaki Basin and on to the Western Platform as the Giant Foresets Formation, thereby building up the modern shelf and slope. Fifth and 6th order sequences are well expressed in the shelf deposits (top-sets) of the upper parts of the Whangamomona and Rangitikei megasequences. They typically have a distinctive sequence architecture comprising shellbed (TST), siltstone (HST) and sandstone (RST) beds. Manutahi-1, which was continuously cored, provides calibration of this sequence architecture to wireline log character, thereby enabling shelf deposits to be mapped widely in the subsurface via the wireline data for hydrocarbon exploration holes. Similar characterization of slope-sets and bottom-sets is work ongoing. The higher order (eustatic) sequences profoundly influenced the local reservoir architecture and seal properties of formations, whereas the megasequence progradation has been responsible for the regional hydrocarbon maturation and migration. Major late tilting, uplift and erosion affected all three basins and created a regional high along the eastern Margin of Taranaki Basin, thereby influencing the migration paths of hydrocarbons sourced deeper in the basin and allowing late charge of structural and possibly stratigraphic traps

Megasequence architecture of Taranaki, Wanganui, and King Country basins and Neogene progradation of two continental margin wedges across western New Zealand.

Taranaki, Wanganui and King Country basins (formerly North Wanganui Basin) have been regarded as discrete basins, but they contain a very similar Neogene sedimentary succession and much of their geological history is held in common. Analysis of the stratigraphic architecture of the fill of each basin reveals the occurrence of four 2nd order megasequences of tectonic origin. The oldest is the early-early Miocene (Otaian Stage) Mahoenui Group/megasequence, followed by the late-early Miocene (Altonian Stage) Mokau Group/megasequence (King Country Basin), both of which correspond to the lower part of the Manganui Formation in Taranaki Basin. The third is the middle to late Miocene Whangamomona Group/megasequence, and the fourth is the latest Miocene-Pleistocene Rangitikei Supergroup/megasequence, both represented in the three basins. Higher order sequences (4th, 5th, 6th), having a eustatic origin, are evident in the Whangamomona and Rangitikei megasequences, particularly those of 5th order with 41 ka periodicity. The distribution of the megasequences are shown in a series of cross-section panels built-up from well -to-well correlations, complemented by time-stratigraphic cross-sections. The base of each megasequence is marked by marine flooding and represents a discrete phase in basin development. For the first megasequence this corresponded to rapid subsidence of the King Country Basin in a compressional setting and basement overthrusting on the Taranaki Fault, with the rapid introduction of terrigenous sediment during transgression. The Mahoenui megasequence accumulated mostly at bathyal depths; no regressive deposits are evident, having been eroded during subsequent uplift. The second (Mokau) megasequence accumulated during reverse movement on the Ohura Fault, formation of the Tarata Thrust Zone, and onlap of the basement block between the Taranaki Fault and the Patea-Tongaporutu-Herangi High (PTH). The Whangamomona megasequence accumulated during extensive reflooding of King Country Basin, onlap of the PTH High and of basement in the Wanganui Basin. This is an assymetrical sequence with a thin transgressive part (Otunui Formation) and a thick regressive part (Mount Messenger to Matemateaonga Formations). It represents the northward progradation of a continental margin wedge with bottom-set, slope-set and top-set components through Wanganui and King Country basins, with minor progradation over the PTH High and into Taranaki Basin. The Rangitikei megasequence is marked by extensive flooding at its base (Tangahoe Mudstone) and reflects the pull-down of the main Wanganui Basin depocentre. This megasequence comprises a second progradational margin wedge, which migrated on two fronts, one northward through Wanganui Basin and into King Country Basin, and a second west of the PTH High, through the Toru Trough and into the Central and Northern Grabens of Taranaki Basin and on to the Western Platform as the Giant Foresets Formation, thereby building up the modern shelf and slope. Fifth and 6th order sequences are well expressed in the shelf deposits (top-sets) of the upper parts of the Whangamomona and Rangitikei megasequences. They typically have a distinctive sequence architecture comprising shellbed (TST), siltstone (HST) and sandstone (RST) beds. Manutahi-1, which was continuously cored, provides calibration of this sequence architecture to wireline log character, thereby enabling shelf deposits to be mapped widely in the subsurface via the wireline data for hydrocarbon exploration holes. Similar characterization of slope-sets and bottom-sets is work ongoing. The higher order (eustatic) sequences profoundly influenced the local reservoir architecture and seal properties of formations, whereas the megasequence progradation has been responsible for the regional hydrocarbon maturation and migration. Major late tilting, uplift and erosion affected all three basins and created a regional high along the eastern Margin of Taranaki Basin, thereby influencing the migration paths of hydrocarbons sourced deeper in the basin and allowing late charge of structural and possibly stratigraphic traps

Neogene stratigraphic architecture and tectonic evolution of Wanganui, King Country, and eastern Taranaki Basins, New Zealand

Analysis of the stratigraphic architecture of the fills of Wanganui, King Country, and eastern Taranaki Basins reveals the occurrence of five 2nd order Late Paleocene and Neogene sequences of tectonic origin. The oldest is the late Eocene-Oligocene Te Kuiti Sequence, followed by the early-early Miocene (Otaian) Mahoenui Sequence, followed by the late-early Miocene (Altonian) Mokau Sequence, all three in King Country Basin. The fourth is the middle Miocene to early Pliocene Whangamomona Sequence, and the fifth is the middle Pliocene-Pleistocene Rangitikei Sequence, both represented in the three basins. Higher order sequences (4th, 5th, 6th) with a eustatic origin occur particularly within the Whangamomona and Rangitikei Sequences, particularly those of 6th order with 41 000 yr periodicity

Photonic Artifacts in Ratiometric Luminescence Nanothermometry

Ongoing developments in science and technology require temperature measurements at increasingly higher spatial resolutions. Nanocrystals with temperature-sensitive luminescence are a popular thermometer for these applications offering high precision and remote read-out. Here, we demonstrate that ratiometric luminescence thermometry experiments may suffer from systematic errors in nanostructured environments. We place lanthanide-based luminescent nanothermometers at controlled distances of up to 600 nm from a Au surface. Although this geometry supports no absorption or scattering resonances, distortion of the emission spectra of the thermometers due to the modified density of optical states results in temperature read-out errors of up to 250 K. Our simple analytical model explains the effects of thermometer emission frequencies, experimental equipment, and sample properties on the magnitude of the errors. We discuss the relevance of our findings in several experimental scenarios. Such errors do not always occur, but they are expected in measurements near reflecting interfaces or scattering objects

Size-Dependent Optical Properties of InP Colloidal Quantum Dots

Indium phosphide colloidal quantum dots (CQDs) are the main alternative for toxic and restricted Cd based CQDs for lighting and display applications. Here we systematically report on the size-dependent optical absorption, ensemble, and single particle photoluminescence (PL) and biexciton lifetimes of core-only InP CQDs. This systematic study is enabled by improvements in the synthesis of InP CQDs to yield a broad size series of monodisperse core-only InP CQDs with narrow absorption and PL line width and significant PL quantum yield

High-Throughput Characterization of Single-Quantum-Dot Emission Spectra and Spectral Diffusion by Multiparticle Spectroscopy

In recent years, quantum dots (QDs) have emerged as bright, color-tunable light sources for various applications such as light-emitting devices, lasing, and bioimaging. One important next step to advance their applicability is to reduce particle-to-particle variations of the emission properties as well as fluctuations of a single QD’s emission spectrum, also known as spectral diffusion (SD). Characterizing SD is typically inefficient as it requires time-consuming measurements at the single-particle level. Here, however, we demonstrate multiparticle spectroscopy (MPS) as a high-throughput method to acquire statistically relevant information about both fluctuations at the single-particle level and variations at the level of a synthesis batch. In MPS, we simultaneously measure emission spectra of many (20-100) QDs with a high time resolution. We obtain statistics on single-particle emission line broadening for a batch of traditional CdSe-based core-shell QDs and a batch of the less toxic InP-based core-shell QDs. The CdSe-based QDs show significantly narrower homogeneous line widths, less SD, and less inhomogeneous broadening than the InP-based QDs. The time scales of SD are longer in the InP-based QDs than in the CdSe-based QDs. Based on the distributions and correlations in single-particle properties, we discuss the possible origins of line-width broadening of the two types of QDs. Our experiments pave the way to large-scale, high-throughput characterization of single-QD emission properties and will ultimately contribute to facilitating rational design of future QD structures

Ototopical drops containing a novel antibacterial synthetic peptide: safety and efficacy in adults with chronic suppurative otitis media

ObjectiveChronic suppurative otitis media (CSOM) is a chronic infectious disease with worldwide prevalence that causes hearing loss and decreased quality of life. As current (antibiotic) treatments often unsuccessful and antibiotic resistance is emerging, alternative agents and/or strategies are urgently needed. We considered the synthetic antimicrobial and anti-biofilm peptide P60.4Ac to be an interesting candidate because it also displays anti-inflammatory activities including lipopolysaccharide-neutralizing activity. The aim of the present study was to investigate the safety and efficacy of ototopical drops containing P60.4Ac in adults with CSOM without cholesteatoma.MethodsWe conducted a range-finding study in 16 subjects followed by a randomized, double blinded, placebo-controlled, multicentre phase IIa study in 34 subjects. P60.4Ac-containing ototopical drops or placebo drops were applied twice a day for 2 weeks and adverse events (AEs) and medication use were recorded. Laboratory tests, swabs from the middle ear and throat for bacterial cultures, and audiometry were performed at intervals up to 10 weeks after therapy. Response to treatment was assessed by blinded symptom scoring on otoscopy.ResultsApplication of P60.4Ac-containing ototopical drops (0.25-2.0 mg of peptide/ml) in the ear canal of patients suffering from CSOM was found to be safe and well-tolerated. The optimal dose (0.5 mg of peptide/ml) was selected for the subsequent phase IIa study. Safety evaluation revealed only a few AEs that were unlikely related to study treatment and all, except one, were of mild to moderate intensity. In addition to this excellent safety profile, P60.4Ac ototopical drops resulted in a treatment success in 47% of cases versus 6% in the placebo group.ConclusionThe efficacy/safety balance assessed in the present study provides a compelling justification for continued clinical development of P60.4Ac in therapy-resistant CSOM.Development and application of statistical models for medical scientific researc

Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced