Shells of crystal field symmetries evidenced in oxide nano-crystals.

By the use of a point charge model based on the Judd-Ofelt transition theory, the luminescence from Eu(3+) ions embedded in Gd(2)O(3) clusters is calculated and compared to the experimental data. The main result of the numerical study is that without invoking any other mechanisms such as crystal disorder, the pure geometrical argument of the symmetry breaking induced by the particle surface has an influence on the energy level splitting. The modifications are also predicted to be observable in realistic conditions where unavoidable size dispersion has to be taken into account. The emission spectrum results from the contribution of three distinct regions; a cluster core, a cluster shell and the very surface, the latter being almost completely quenched in realistic conditions. Eventually, by detailing the spectra of the ions embedded at different positions in the cluster we get an estimate of about 0.5 nm for the extent of the crystal field induced Stark effect. Due to the similarity between Y (2)O(3) and Gd(2)O(3), these results also apply to Eu(3+) doped Y(2)O(3) nanoparticles.

Facile and rapid synthesis of highly luminescent nanoparticles via pulsed laser ablation in liquid.

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S:Eu3+, Gd2SiO5:Ce3+, Lu3TaO7:Gd3+ and Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states, etc).

Fluorescent oxide nanoparticles adapted to active tips for near-field optics.

We present a new kind of fluorescent oxide nanoparticle (NP) with properties well suited to active-tip based near-field optics. These particles with an average diameter in the 5-10 nm range are produced by low energy cluster beam deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), cathodoluminescence, near-field scanning optical microscopy (NSOM) and fluorescence in the photon-counting mode. Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.

Vector modulation instability induced by vacuum fluctuations in highly birefringent fibers in the anomalous-dispersion regime.

We report a detailed experimental study of vector modulation instability in highly birefringent optical fibers in the anomalous-dispersion regime. We prove that the observed instability is mainly induced by vacuum fluctuations. The detuning of the spectral peaks agrees with linear perturbation analysis. The exact shape of the spectrum is well reproduced by numerical integration of stochastic nonlinear Schrödinger equations describing quantum propagation.

Provably secure experimental quantum bit-string generation.

Coin tossing is a cryptographic task in which two parties who do not trust each other aim to generate a common random bit. Using classical communication this is impossible, but nontrivial coin tossing is possible using quantum communication. Here we consider the case when the parties do not want to toss a single coin, but many. This is called bit-string generation. We report the experimental generation of strings of coins which are provably more random than achievable using classical communication. The experiment is based on the "plug and play" scheme developed for quantum cryptography, and therefore well suited for long distance quantum communication.