The versatile photophysical properties of lanthanide ions [1] have inspired vigorous research activities owing to a wide range of potential applications in the fields of bioassays, [2] sensor systems, [3] and optical materials. [4] The Eu 3+ and Tb 3+ ions are of particular interest owing to their long luminescence lifetime and narrow emission bands in the visible region. Some other lanthanide ions were also investigated for their near-infrared luminescence or diagnostic properties. [5] Recently, the electroluminescence of lanthanide ions has attracted increasing attention as potential light-emitting materials in light-emitting diodes (LEDs), and a number of Eu 3+ and Tb 3+ complexes have been incorporated into LED devices.[6] Compared with other lanthanide ions, the Ce 3+ ion is unique, characteristic of parity-allowed electric-dipole 4f! 5d transitions, which lead to fast decay times and high light outputs. [7] Great endeavors have been devoted to doping Ce 3+ ions into inorganic crystals to serve as metal phosphors with possible applications in solid-state lasers, quantum cutters, inorganic scintillators, and fluorescent lamps and displays. [7] By contrast, investigations of the luminescence properties of Ce 3+ ion in organic coordination environments remain rather rare, although that of the free Ce 3+ ion has been thoroughly studied [8] and its luminescence in Ce 3+ halides, organometallics, and polymer films has been studied. [9] It is well known that although the inner 4f orbitals of Ce 3+ are well shielded, their 5d orbitals are very sensitive to the ligand sphere. Many organic ligands have been found to quench Ce 3+ luminescence upon complexation, and contact of Ce 3+ ions with solvent molecules may engender nonradiative transitions to diminish the luminescence.[8] Nevertheless, studies have indicated that diazapolyoxabicyclic ligands (cryptands) could well shield the Ce 3+ ions and result in efficient luminescence in the ultraviolet region.[10] Some Ce 3+ complexes containing halide anions and certain carboxylate groups were also found to be luminescent, and the emission bands were remarkably red-shifted into the visible region up to 630 nm depending on the interactions of the 5d energy levels with the crystal field. [9,11] These findings suggest that, in principle, highly luminescent Ce 3+ complexes are achievable provided that a suitable organic ligand is designed to encapsulate the Ce 3+ ion. More important, as the ligand can be readily modified and decorated to provide an adjustable crystal field, the use of the Ce 3+ chromophore in luminescent materials can potentially offer tunable emission wavelength and strength, covering the UV and Vis regions. [7][8][9][10][11] Taking into account the well-studied red-emitting Eu 3+ complexes and green-emitting Tb 3+ complexes in LEDs, luminescent Ce 3+ complexes may provide an alternative as light-emitters in LED devices, in contrast with the commonly studied inorganic systems. [12] We and others [13] have studied lanthanide complexes with tripodal...

Coherent transition radiation in the terahertz (THz) region with energies of sub-mJ/pulse has been demonstrated by relativistic laser-driven electron beams crossing the solid-vacuum boundary.Targets including mass-limited foils and layered metal-plastic targets are used to verify the radiation mechanism and characterize the radiation properties. Observations of THz emissions as a function of target parameters agree well with the formation-zone and diffraction model of transition radiation.Particle-in-cell simulations also well reproduce the observed characteristics of THz emissions. The present THz transition radiation enables not only a potential tabletop brilliant THz source, but also a novel noninvasive diagnostic for fast electron generation and transport in laser-plasma interactions.

Hard X-ray sources from femtosecond (fs) laser-produced plasmas, including the betatron X-rays from laser wakefield-accelerated electrons, have compact sizes, fs pulse duration and fs pump-probe capability, making it promising for wide use in material and biological sciences. Currently the main problem with such betatron X-ray sources is the limited average flux even with ultra-intense laser pulses. Here, we report ultra-bright betatron X-rays can be generated using a clustering gas jet target irradiated with a small size laser, where a ten-fold enhancement of the X-ray yield is achieved compared to the results obtained using a gas target. We suggest the increased X-ray photon is due to the existence of clusters in the gas, which results in increased total electron charge trapped for acceleration and larger wiggling amplitudes during the acceleration. This observation opens a route to produce high betatron average flux using small but high repetition rate laser facilities for applications.

New parasitic lasing suppression techniques are developed and high gain amplification is demonstrated in a petawatt level Ti:sapphire amplifier based on the chirped pulse amplification (CPA) scheme. Cladding the large aperture Ti:sapphire with refractive-index matched liquid doped with absorber suppresses the transverse lasing. The acousto-optic programmable dispersive filter (AOPDF) is used to realize side-lobe suppression in the temporal profile of the compressed pulse. The 800 nm laser output with peak power of 0.89 PW and pulse width of 29.0 fs is demonstrated.