Optical properties and energy transfer processes in Tb3+-doped ZnSe quantum dots.

Tb3+-Doped ZnSe quantum dots (QDs) with a Tb content in the range of 0.5-7% were successfully synthesized by a wet chemical method. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed that the as-synthesized QDs had a zinc blende (ZB) structure with a particle size of approximately 4 nm. The effect of Tb-doping on the structure and optical properties of the ZnSe QDs was studied. The emission spectra and photoluminescence (PL) decay kinetics data confirmed the successful incorporation of Tb3+ ions into the ZnSe host. The PL spectra also revealed that the intensity of dopant emission was significantly enhanced owing to the energy transfer (ET) from the host emission. The efficiency of the ET process from the ZnSe host to Tb3+ ions and between Tb3+ ions and the nature of these interaction mechanisms were determined by applying the Inokuti-Hirayama and Reisfeld models. The features of the ligand field and the optical properties of Tb3+ ions in the ZnSe QDs were studied using Judd-Ofelt theory. The dependence of the chromaticity features of ZnSe:Tb3+ QDs on the Tb concentration was estimated by the chromaticity coordinates and correlated color temperature (CCT). The Tb3+-doped ZnSe QDs with visible, tunable, and very long lifetime emission have potential for practical applications such as biological labeling, photocatalysis, and white-LED devices.

Effect of dopant concentration and the role of ZnS shell on optical properties of Sm3+ doped CdS quantum dots.

The role of samarium (Sm) dopant on the structural, morphological, and optical properties of CdS QDs and CdS/ZnS core/shell QDs was methodically reported. The synthesis of Sm-doped CdS QDs and CdS/ZnS QDs was carried out via a facile wet chemical method. The structure, chemical composition, and optical properties of the synthesized QDs were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and photoluminescence (PL) spectroscopy. XRD analysis showed that the synthesized CdS QDs exhibited zinc blende structure which was not affected by doping Sm3+ ions. The particle size of the CdS:Sm and CdS:Sm (2%)/ZnS QDs was estimated to be ∼4 nm and ∼7 nm, respectively. Transmission electron microscopy (TEM) images revealed that the incorporation of Sm dopant did not significantly affect the size and morphology of CdS QDs, while the formation of the ZnS shell increased the particle size. XPS and XRD results confirmed the successful incorporation of Sm3+ ions into the CdS QDs. The effect of dopant concentration on the structural and luminescent properties was studied. The emission and excitation spectra of Sm3+-doped CdS QDs and CdS/ZnS QDs consisted of the characteristic lines corresponding to the intra-configurational f-f transitions. The energy transfer (ET) mechanism from the host to Sm3+ ions and the ET process through cross-relaxation between Sm3+ ions have been elucidated. The effect of the ZnS shell on the optical stability of the Sm3+-doped CdS QDs was studied in detail and the results showed that the CdS:Sm (2%)/ZnS QDs retained their good emission characteristics after 376 days of fabrication. The luminescent properties of Sm-doped QDs ranging from violet to red and PL lifetime extending to milliseconds demonstrated that these QDs are the potential materials for applications in white LEDs, biomarkers, and photocatalysis.

New insights on the energy transfer mechanisms of Eu-doped CdS quantum dots.

Eu-doped CdS quantum dots (QDs) with the Eu dopant concentration in the range of 0.5-10% and zinc blende (ZB) structure were successfully synthesized by a wet chemical method. The fabricated Eu-doped CdS QDs exhibited emissions in the visible window approximately at 465, 590, 618 and 696 nm, which correspond to the excitonic emission of CdS QDs and the electronic transitions of the intra 4f6 configuration from the 5D0 level to 7F1, 7F2 and 7F4 levels of Eu3+ dopant ions, respectively. Judd-Ofelt theory was used to estimate the properties of ligand field and luminescence quantum efficiency of the material. The interaction mechanism and the efficiency of the energy transfer process from CdS QDs to Eu3+ ions were found by using Reisfeld's approximation formulas. The luminescence quenching of Eu3+-doped CdS QDs was studied through analysis of emission spectra and decay curves. The dominant interaction mechanism between Eu3+ ions and energy transfer parameters have been found by fitting the decay curves to the Inokuti-Hirayama model. The cross-relaxation channels leading to the luminescence quenching of Eu3+ have also been predicted.

Influence of precursor ratio and dopant concentration on the structure and optical properties of Cu-doped ZnCdSe-alloyed quantum dots.

Tunable copper doped Zn1-x Cd x S alloy quantum dots (QDs) were successfully synthesized by the wet chemical method. A one-step method is developed to synthesize doped ternary QDs which is more preferable than a two-step method. The influence of experimental parameters like the Zn/Cd ratio and Cu dopant concentration has been investigated using various spectroscopic techniques like UV-visible, photoluminescence, X-ray diffraction and Raman spectroscopy. The absorption and emission properties can be tuned by changing the concentration of components of the ternary QDs. The high concentration of dopant completely quenched the emission of the ternary QDs. EDX gives confirmation of the elemental composition of the synthesized samples. The obtained results suggest the successful doping of the ternary QDs. Interestingly, the study results revealed that the crystal structure (ZB and/or WZ) and the dual emission of the Cu-doped Zn1-x Cd x Se alloy QDs could be controlled by varying the dopant concentration and chemical composition of the host. Doping also leads to enhancement in emission properties and provides more stability to ternary QDs. The enhancement in the photoluminescence (PL) decay lifetime of Cu-doped ternary QDs can be advantageous for optoelectronic and biosensor applications.

Impact of urban expansion on the air pollution landscape: A case study of Hanoi, Vietnam.

The rapid urban expansion of Hanoi over the last few decades has transformed a lot of agricultural land into urban land uses accompanying pollution by traffic, industrial, and residential emission sources. In this work, the impact of urban expansion on the air pollution landscape has been assessed using the NO2 and SO2 ambient concentrations measured by passive diffusion samplers at 176 sites across the nine urban and the five peri-urban districts of Hanoi spanning an area of 921 km2. The NO2 values ranged from 5.5 to 70 µg m-3 with an arithmetic mean of 34.3 µg m-3. The corresponding figures for SO2 are 1, 51, and 14.5 µg m-3. The pollutant concentrations decrease from the city center outward, reflecting the history of urban expansion with the city fringe being urbanized in the 1980s and the peri-urban area having undergone development from the early 1990s. The pollution landscapes show elevated concentration levels in the recently built-up areas at 6, 10, and 21 km from the city center. The NO2 and SO2 digital maps generated from monitoring data by the kriging technique show numerous traffic and industrial emission hot spots in the peri-urban area. As revealed by the land use regression models, the factors driving the spatial variations of pollutant concentrations across the city include the population density, the road density, and the distances of the monitoring site to the urban center and the nearest roadway.

The role of fluid temperature and form on endurance performance in the heat.

Exercising in the heat often results in an excessive increase in body core temperature, which can be detrimental to health and endurance performance. Research in recent years has shifted toward the optimum temperature at which drinks should be ingested. The ingestion of cold drinks can reduce body core temperature before exercise but less so during exercise. Temperature of drinks does not seem to have an effect on the rate of gastric emptying and intestinal absorption. Manipulating the specific heat capacity of a solution can further induce a greater heat sink. Ingestion of ice slurry exploits the additional energy required to convert the solution from ice to water (enthalpy of fusion). Body core temperature is occasionally observed to be higher at the point of exhaustion with the ingestion of ice slurry. There is growing evidence to suggest that ingesting ice slurry is an effective and practical strategy to prevent excessive rise of body core temperature and improve endurance performance. This information is especially important when only a fixed amount of fluid is allowed to be carried, often seen in some ultra-endurance events and military operations. Future studies should evaluate the efficacy of ice slurry in various exercise and environmental conditions.

Cold drink attenuates heat strain during work-rest cycles.

There is limited information on the ingestion of cold drinks after exercise. We investigated the thermoregulatory effects of ingesting drinks at 4°C (COLD) or 28°C (WARM) during work-rest cycles in the heat. On 2 separate occasions, 8 healthy males walked on the treadmill for 2 cycles (45 min work; 15 min rest) at 5.5 km/h with 7.5% gradient. Two aliquots of 400 mL of plain water at either 4°C or 28°C were consumed during each rest period. Rectal temperature (T re ), skin temperature (T sk ), heart rate and subjective ratings were measured. Mean decrease in T re at the end of the final work-rest cycle was greater after the ingestion of COLD drinks (0.5±0.2°C) than WARM drinks (0.3±0.2°C; P<0.05). Rate of decrease in T sk was greater after ingestion of COLD drinks during the first rest period (P<0.01). Mean heart rate was lower after ingesting COLD drinks (P<0.05). Ratings of thermal sensation were lower during the second rest phase after ingestion of COLD drinks (P<0.05). The ingestion of COLD drinks after exercise resulted in a lesser than expected reduction of T re . Nevertheless, the reduction in T re implies a potential for improved work tolerance during military and occupational settings in the heat.

Attitudes of the Singapore public to actions suggesting child abuse.

OBJECTIVE: The aim was to ascertain the views of the Singapore public on the acceptability of actions of an abusive nature. METHOD: In-depth interviews were carried out with 401 randomly sampled respondents in relation to a range of actions. Questions were asked concerning the acceptability of 18 actions, whether circumstances might justify eight of them, how respondents felt about reporting child abuse and whether they could recall any case they had come across. RESULTS: Respondents strongly disapproved of sexually motivated acts, and were more disapproving of physical abuse or neglect than of emotional abuse or neglect. Circumstances did affect how the less extreme actions were viewed. Respondents supported reporting child abuse, but were somewhat against mandatory reporting. They were able to recall details of a number of possible cases. CONCLUSION: We argue that definitions of child abuse should be general and not tied to specific actions, since the effects of actions may vary across cultures, and should be treated as an empirical matter. This allows a research agenda that focuses on the consequences of actions rather than issues of definition.

Progressive osseous destruction as a complication of HIV-periodontitis.

A pathologic condition is described, characterized by rampant necrosis of gingival mucosa, periodontium, and related osseous structures associated with systemic infection with the human immunodeficiency virus (HIV). It is believed that this condition is an extension beyond the normal clinical course of HIV-periodontitis (HIV-P) and manifests itself in three progressive stages: (1) HIV-associated gingivitis, (2) HIV-P, and (3) an extension of HIV-P to osseous necrosis. Two cases of osseous destruction attending HIV-P are reported, one of which led to initial diagnosis of HIV infection. They represent the final stage of disease progression with localized necrosis of gingiva, periodontium, and alveolar bone.

A sensitive SV40 viral probe assay for DNA strand breaks and their biological repair in higher cells: techniques and preliminary results.

An alternative experimental approach to the investigation of intracellular repair of DNA strand breaks by mammalian higher cells has been developed using simian virus 40 (SV40), which has no known intrinsic DNA repair capacity and possesses a minichromosome structure, as an intracellular probe. In this approach unirradiated simian or human cells are infected with irradiated virus and incubated for varying periods. Nuclei are isolated, and viral DNA is extracted and assayed for residual damage. This assay involves separation of the viral DNA by agarose gel electrophoresis into three sharply demarcated bands corresponding to DNA molecules containing a double-strand break (DSB), single-strand breaks (SSB), or no breaks. Quantitative data are obtained by a combination of DNA hybridization with 32P-labeled SV40 DNA, autoradiography, and densitometry. Various experiments have been carried out to investigate the feasibility of this approach and to establish the optimal experimental conditions for its use. These experiments indicate that there is rapid and efficient cellular uptake of SV40. independent of prior radiation dose to the virus, and that this multistep experimental procedure gives excellent recovery and quantitation of the three DNA forms when compared with more direct methods of measurement. Radiation dose-response experiments with purified extracellular SV40 virus, using this approach, are quite reproducible and give results closely comparable to those obtained with techniques in current use. Initial time-course incubation experiments with SV40 infected CV-1 monkey kidney cells indicate that this approach can demonstrate slow but extensive intracellular repair of SSB; and limited presumptive early repair of DSB, followed by later and more extensive induction of DSB.