Luminescent nanocrystals can find interesting applications for the elaboration of light emitting transparent materials. The work described here is based on the use of lanthanide doped vanadate (YVO4:Eu) and phosphate (La, Ce, Tb)PO4-0, 7H2O nanoparticles grown through aqueous colloidal synthesis, with average sizes below 10 nm. The well-dispersed colloids are transparent and respectively exhibit red and green luminescence under U.V. excitation with high luminescence yields (20 – 50 %). Improvement of luminescence properties of the nanocrystals is achieved through the elaboration of core/shell nanostructures, obtained after the growth at the surface of an amorphous silica shell or a crystalline lanthanum phosphate shell. Surface derivatization is further achieved through the controlled growth of an organically modified silica coating using a functionalized silane precursor. Concentrated sols are obtained, which are highly luminescent and well-dispersed. They can be spin-coated on various substrates, leading to perfectly transparent and highly luminescent thin films. Multi-layers films and heating treatments are performed, leading to optimized materials.

We present a theory of two-photon absorption in solutions which addresses the formation of spectral shapes taking account of the vibrational degrees of freedom. The theory is used to rationalize observed differences between spectral shapes of one- and two-photon absorption. We elaborate on two underlying causes, one trivial and one non-trivial, behind these differences. The first refers simply to the fact that the set of excited electronic states constituting the spectra will have different relative cross sections for one-and two- photon absorption. The second reason is that the two-step and coherent two-photon absorption processes are competing, making the one-and two-photon spectral bands different even considering a single final state. The theory is applied to the N-101 molecule [di-phenyl-amino-nitro-stilbene] which was recently studied experimentally in the paper [ T.-C. Lin, G.S. He, P.N. Prasad, and L.-S. Tan, J. Mater. Chem., 14, 982, 2004.]

The time dependent density functional theory (TDDFT) has applied to study the optical responses of the conjugated polymers such as poly(p-phenylenevinylene) and poly(9, 9-dialkyl-fluorene). In our study, the real-space grid representation is used for the electron wavefunctions in contrast to a conventional basis set on each atom. In the calculations of the optical responses, the real-time approach is employed, where we follow the linear responses of the systems under externally applied perturbations in the real time. Since a real polymer is too large to handle, we have calculated the oligomers with different length and observed the spectrum peak is redshifted as the length of oligomer increases. The property of the polymer is extrapolated as the infinitely long oligomer. The estimated polymer spectra agree with the experiments reasonably well.

Noble metal-coated polydiacetylene (PDA) nanocrystals are expected to enlarge effective third-order nonlinear optical susceptibility, owing to the enhancement of optical electric field induced by localized surface plasmon. The surface of PDA nanocrystals was decorated with silver nanoparticles, and the linear optical properties were investigated. The well-defined PDA nanocrystals were first prepared by the conventional reprecipitation method as an aqueous dispersion. The following two-steps of reduction methods, namely, seed deposition and seed growth, enabled higher silver coverage on the surface of PDA nanocrystals. Silver fine seeds were successfully deposited on the PDA surface by particularly employing an anionic surfactant as a binder. The extinction spectra of the PDA nanocrystals covered with silver exhibited the red-shift and broadening of surface plasmonic peak for silver nanoparticles, which would indicate the interaction among silver nanoparticles on the same PDA nanocrystal. In addition, the red-shift of excitonic peak for PDA nanocrystals was observed, resulting from the changes of dielectric properties around PDA nanocrystal. Both spectral changes would have an influence on nonlinear optical properties of PDA nanocrystal.

We accurately measured the absolute photoluminescence (PL) quantum efficiency (ηPL) of organic solid-state thin films by using an integrating sphere. We measured the ηPL of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq3), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4, 4'-bis(carbazol-9-yl)-2, 2'-biphenyl [Ir(ppy)3:CBP] co-deposited film. Alq3 and Ir(ppy)3:CBP showed a ηPL = 20 ± 1% and 97 ± 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-N, C3'] (acetylacetonato) iridium(III) [Btp2Ir(acac)] with CBP, and the blue complex, bis[(4, 6-difluorophenyl)pyridinato-N, C2](picolinato)iridium(III) [FIrpic], with m-bis(N -carbazolyl)benzene. The maximum ηPL values for Btp2Ir(acac), and FIrpic were 51±1% (at 1.4mol%), and 99±1% (1.2mol%), respectively. These results suggest that the ηEL of red phosphorescent OLEDs using Btp2Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.

We present results for linear and nonlinear light scattering experiments from percolative silver nanoshells on dielectric silica cores. Using ultrashort pulsed laser illumination we observe strong nonlinear optical (NLO) responses from single metallodielectric core-shell (MDSC) spheres and disordered MDSC sphere aggregates. Finally, combining scaling theory with core-shell Mie scattering formalism we obtain a new model for the observed linear extinction signals.

Eu3+ doped Y2O3 and Lu2O3 nanocrystalline powders were synthesized via combustion technique using urea as a fuel and the metal nitrates as oxidants. The compacted nanopowders were vacuum sintered in order to form the translucent ceramics. A significant enhancement of emission characteristics was observed from the ceramics synthesized from the nanoparticles by controlling the vacuum-sintering conditions. Although the processed ceramics display superior emission characteristics, the nanocrystalline phosphor powders also display reasonably good emission characteristics. Highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films were deposited on various substrates under different growth and optimization conditions using pulsed-laser deposition technique using high-density translucent ceramic target. Superior spectroscopic performance was obtained on films grown on sapphire substrates due to high-quality and epitaxial nature of the film.