The synthesis of garnet-type Gd3Sc2Al3O12 (GSAG) nanoparticles doped with Ce3+ ions under solvothermal conditions in 1,4-butanediol is reported in this work. X-ray diffraction with LeBail fitting, Electron microscopy images and photoluminescence spectra were used to characterize the samples. A detailed Transmission Electron Microscopy study shows strong modification of particle morphology upon reaction temperature. Performing the reaction at high temperature and high pressure leads to a clear increase of the particle crystallinity and allows the formation of 100-nm sized nanocrystals with a small size dispersion (± 20 nm). The formation mechanism of these particles is through the self-orientation of primary crystalline grains. Yellow-orange luminescence of Ce3+-doped GSAG nanoparticles is observed upon 457-nm excitation. Photoluminescence intensity drastically increases when the particles are synthesized at high temperature, which is directly correlated to their crystal quality.
Scalability of optical devices is a major challenge for quantum optics and quantum cryptography fields. However, non-linear optical processes such as second harmonic generation (SHG) and parametric-down conversion become very inefficient when the active medium is reduced to the nanoscale. Enhancement strategies are therefore mandatory.
Here, we first investigate the role of plasmonic resonances in single aluminum nanostructures allowing doubly resonant and mode-matched conditions. We show that the SHG rate can be 36-fold enhanced compared to non-resonant structures. We further infer the origin of the nonlinearity by quantitatively comparing simulated and measured SHG maps obtained by scanning the antennas under a tightly focused beam.
The SHG response of a KTP nano-crystal and its modification by the proximity of a plasmonics antenna can then be confidently modeled. We show that the harmonic photon production yield is comparable for a bare nano-crystal and a doubly resonant aluminum antenna, despite the centro-symmetric nature of the latter. Combining the nonlinearity of the KTP crystal and the field enhancements provided by the plasmonic structure at both fundamental and harmonic frequency, we demonstrate that the SHG signal can be magnified by more than two orders of magnitude. The anticipated efficiency of the hybrid nonlinear plasmonic structures is compared to experiments performed at the single structure level, emphasizing the crucial role of the nanocrystal orientation.
We present the stable trapping of luminescent 300-nm cerium-doped YAG particles in aqueous suspension using a dual fiber tip optical tweezers. The particles were elaborated using a specific glycothermal synthesis route together with an original protected annealing step. We obtained harmonic trap potentials in the direction transverse to the optical fiber axes. In the longitudinal direction, the potential shows some sub-structure revealed by two peaks in the distribution statistics with a distance of about half the wavelength of the trapping laser. We calculated intensity normalized trapping stiffness of 36 pN•μm-1W-1. These results are compared to previous work of microparticle trapping and discussed thanks to numerical simulations based on finite element method.
We considered luminescent TiO 2 films whose surface was imprinted with a two-dimensional (2-D) square shaped photonic crystal with different pattern depths (from 20 to 61 nm). The aim of this work is to develop a straightforward method to characterize the PhC efficiency on light extraction. Transmission spectra of the patterned areas as obtained using a routine spectrometer exhibit peaks evidencing the coupling by the photonic crystal structure of free-space light with guided modes within the film, in good agreement with 2-D rigorous-coupled wave analysis (RCWA) simulations. As expected, the deeper the pattern depth, the stronger the coupling between the guided light and the photonic crystal. RCWA simulations allow evaluating quantitatively the extraction length, characteristic of the efficiency of light extraction, from the transmission spectra, in good agreement with direct measurements.
Considering luminescent TiO2 films whose surface was imprinted with a 2D square shaped photonic crystal with different pattern depths (from 20 to 61 nm), we demonstrate the possibility to use simple absorption measurements to evaluate the efficiency of light extraction. Absorption spectra of the patterned systems show absorption peaks, evidencing the coupling between the photonic crystal structure and light guided within the film, in good agreement with 2D-RCWA simulations. The deeper the pattern depth, the stronger the coupling between the guided light and the photonic crystal. Using RCWA simulations, we show that it is possible to evaluate the extraction length, characteristic of the efficiency of light extraction, from the absorption spectra, in good agreement with direct measurements reported elsewhere.
Neurons display dendritic spines plasticity and morphology anomalies in numerous psychiatric and neurodegenerative
diseases. These changes are associated to abnormal dendritic traffic that can be evidenced by fluorescence microscopy.
As a fluorescent probe we propose to use fluorescent diamond nanoparticles with size of < 50 nm. Color centers
embedded inside the diamond nanoparticles are perfectly photostable emitters allowing for long-term tracking.
Nanodiamond carbon surface is also well suited for biomolecule functionalization to target specific cellular
compartments. We show that fluorescent nanodiamonds can be spontaneously internalized in neurons in culture and
imaged by confocal and Total Internal Reflection (TIRF) microscopy with a high signal over background ratio.
Our work is devoted to the development of YAG:Ce3+ nanoparticle based films for white LEDs. Very stable
suspensions of YAG:Ce nanoparticles are synthesized by a glycothermal method at relatively low temperature (300°C).
A protected annealing in a silica matrix allows further treatment of these nanoparticles at high temperature without any
aggregation and growth and with a significant improvement of their quantum yield and photostability. The obtained
colloidal nanoparticles are finally incorporated into different matrices to be used as converter layer for white LEDs. First,
the incorporation in epoxy caps confirms that the annealed particles are much more efficient than the as-made ones and
leads to white light generation. YAG:Ce nanoparticles are also dispersed into a sol-gel matrix of TiO2. Thanks to the
relative matching of refractive indexes between TiO2 and YAG, and to the sub-wavelength particles size, YAG/TiO2films are not scattering, contrary to the same film containing the commonly used micron size phosphor. Nevertheless,
they are not absorbent enough. Thus, YAG:Ce suspensions are then spray-coated to obtain thicker and non diluted films.
These films are a bit scattering but this can be solved by filling their porosity with a high refractive index matrix. A
yellow component is detected when deposited onto a blue LED, meaning that they absorb much more than the
YAG:Ce/TiO2 system. When used as light converters for white LEDs, these spray-coated films could offer the
opportunity to diminish the backscattered light absorption losses.
We report here a method to enhance light extraction from the top face of a TiO2 waveguide doped with a molecular
emitter. Sol-gel TiO2 surface is patterned by a 2D photonic crystal with a 400-nm period and a 40-nm depth, as verified
by Scanning Electron Microscopy and Atomic Force Microscopy. We evidence that light emitted in the TiO2 layer is
efficiently extracted by the surface patterning and quantify the extraction enhancement by measuring the emission
spectra as a function of the emission angle. We measured an enhancement factor of 3 within 50° off normal.