From gold nanobipyramids to nanojavelins for a precise tuning of the plasmon resonance to the infrared wavelengths: experimental and theoretical aspects.

Anisotropic gold nanoparticles and in particular with shapes exhibiting tips are known to present an extremely strong localized electromagnetic field. This field is mostly located at the top of the tips and can be used in various optical applications. Moreover, as a consequence of their anisotropy, they present two plasmon resonance bands corresponding to the transverse and longitudinal resonance modes. Tuning the aspect ratio it becomes possible to display SPR bands near the near infrared region. This was particularly investigated in the case of nanorods and also for bipyramids. In this paper we report a high yield synthesis approach that allows one to precisely control the aspect ratio of bipyramids and to elongate the structure until they adopt a javelin-like aspect. We were able to prepare nano-javelins with surface plasmon resonances up to 1850 nm, opening important perspectives in terms of optical applications in the NIR and IR regions. The synthetic methods are fully reported and the optical properties were correlated with the theoretical approach, taking into consideration not only the aspect ratio but also the truncation of the nano-objects.

Plasmonic bipyramids for fluorescence enhancement and protection against photobleaching.

A great number of studies focus their interest on the photophysical properties of fluorescent hybrid gold nanoparticles for potential applications in biotechnologies such as imaging and/or treatment. Spherical gold nanoparticles are known to quench a chromophore fluorescent signal, when moieties are located in their close vicinity. The use of a polymer spacer on such a system allowed only partial recovery of the dye emission by controlling the surface to dye distance. Gold-based anisotropic sharp nanostructures appear to exhibit more interesting features due to the strong electric field generated at their edges and tips. In this paper, a complete study of hybrid fluorescent bipyramidal-like gold nanostructures is presented. We describe the chemical synthesis of gold bipyramids functionalized with fluorescent water-soluble polymers and their photophysics both in solution and on a single object. We show that the use of a bipyramidal shape instead of a spherical one leads to total recovery of the fluorescence and even to an enhancement of the emission of the dyes by a factor of 1.4.

A site-selective spectroscopy of naphthalene and quinoline in TEOS/MTEOS xerogels.

Fluorescence and phosphorescence spectra and decay times are recorded upon a narrow-band laser excitation for naphthalene (N) and quinoline (Q) embedded in xerogels prepared from MTEOS/TEOS mixtures, in the 10-300 K temperature range. A site selectivity of the excitation is observed at T <120 K and T <150 K, for N and Q, respectively. In the case of quinoline, different families of sites are characterized. The results are discussed in terms of comparison with the N and Q emission behaviour in other environments, especially in rare-gas matrices.

General medical problems among the offspring of depressed parents: a 10-year follow-up.

OBJECTIVE: To examine the association between both parental and offspring depression and the general medical problems of a sample of offspring at high and low risk for depression. METHOD: Offspring (n = 222) from families with either depressed or nondepressed parents were followed up for a period of 10 years. Data collected included psychiatric diagnoses derived from direct semistructured interviews and history of general medical problems and hospital visits. Rates of medical problems and hospitalizations were calculated, and offspring were stratified by depression status of both parent and offspring. RESULTS: In analyses controlled for sociodemographic factors, offspring depression status was associated with a history of genitourinary disorders, headaches, respiratory disorders, other disorders, and hospitalizations in the offspring, and parental depression was associated with a history of unconsciousness and hospitalization in the offspring. After subjects were stratified by parental depression, significant associations between offspring depression and medical problems were found for only those offspring with a depressed parent. CONCLUSIONS: These findings suggest that a history of parental depression increases the risk for medical problems and hospitalization among depressed offspring. The co-occurrence of general medical and psychological problems among offspring of depressed parents may have implications for the treatment of both depression and comorbid medical disorders.

Toward millions of laser pulses with pyrromethene- and perylene-doped xerogels.

Significant improvements have been obtained for solid-state dye lasers with doped xerogels. By using longitudinal pumping with a frequency-doubled Q-switched Nd: YAG laser, we obtained as much as 86% slope efficiency and 5 x 10(5) pulses lifetime. Furthermore, newly prepared deoxygenated samples exhibited even greater lifetimes.

Soft signs in children of parents with agoraphobia.

OBJECTIVE: To study a proposed relationship between anxiety disorders and neurological soft signs by determining whether children of agoraphobic parents would have an increased prevalence of soft signs compared to children of parents without agoraphobia. METHOD: Family study methodology was used to compare 25 children of agoraphobic adults and 25 age- and sex-matched children of nonagoraphobic adults on a structured soft signs examination and on structured psychiatric interviews. Also, soft signs of 12 agoraphobic adults were compared with soft signs of 16 control adults. RESULTS: Children of agoraphobic adults had significantly more right- and left-side motor slowness on finger tapping and hand patting (p values < .05) than did children of controls. Seventy-six percent of the children of agoraphobic adults had at least one slow motor sign, compared with 28% of the control children (p < .001). There were no significant differences in soft signs between agoraphobic and control adults. CONCLUSIONS: The study provides additional support for a relationship between soft signs and anxiety disorder.

Photostability of dye molecules trapped in solid matrices.

The photostability of dye molecules trapped in transparent solid matrices synthesized by the solgel technique was studied both experimentally and theoretically using a model with numerical and approximate analytical solutions. The model is based on a one-photon photodestruction process with the creation of an absorbing bleached molecule. We give the number of photons that different trapped dye molecules can absorb on average before they are bleached. Dyes such as Perylene Red, Perylene Orange, Pyrromethenes 567 and 597, Rhodamines 6G and B, DCM, a Xanthylium salt, and Neon Red were investigated; significant differences were observed. Some dye molecules in solvents were also studied; increased stability resulted when the molecules were trapped in solid matrices.

Perylene- and pyrromethene-doped xerogel for a pulsed laser.

Hydrophobic photostable dye molecules such as perylenes or pyrromethenes were trapped in xerogel matrices. Using these new materials as solid-state dye lasers, we have demonstrated efficient laser operation. Slope efficiencies of up to 30% were obtained in the millijoule output-energy range. Tunabilities of up to 60 nm were observed, and more than 150,000 pulses were emitted by the same spot of a given sample when the laser was pumped at millijoule energy levels.