Barium titanate, Ce-doped barium titanate and La- and Zr-doped lead zirconate titanate thin films were prepared on fused-quartz substrate by laser pulsed deposition. The morphologies and microstructures of the films were examined by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The barium titanate and
Ce-doped barium titanate thin films and Zr-doped lead zirconate titanate film are transparent respectively above 322
and 340 nm; while the corresponding optical band gaps are 3.46, 3.48 and 3.46eV. The two-photon absorptions
coefficients for barium titanate and Ce-doped barium titanate thin films are very large, as large as 51.7 and 59.3 cm/GW, respectively. Nonlinear refractive index of PLZT film is 1.3 X 10-6 esu, much higher than organic polymers, CdS-doped glasses and high density Au-dispersed SiO2 composite films. The mechanisms for the strong nonlinear optic susceptibilities and large two-photon absorption appeared in barium titanate and Ce-doped barium titanate and Zr-doped lead zirconate titanate film are discussed. On the basis of first principle calculation the nonlinear optic susceptibility and
nonlinear two-photon absorption in BaTiO3 was performed. The theoretical calculations are in good agreement with
experimental results.
Raman spectroscopy is used to study phonon confinement effect and photoluminescence (PL) for titanium dioxide nanocrystals. A chemical solution process was developed to prepare TiO2 nanocrystals with particle sizes of 6.8 - 27.9 nm. As the grain size decreases, the lowest-frequency Eg mode at 152 cm-1 shows blueshift and broadening. The frequency shift and line width broadening were theoretically studied at different grain sizes of 6.8, 10.3 and 27.9 nm under phonon confinement model, showing good agreement with experimental results. Non-stoichiometry effect was recorded by redshift of the 422 cm-1 Eg mode, libration mode of the oxygen atoms along the c-axis. PL spectrum of the anatase TiO2 nanocrystals was recorded at exciting power as low as 0.06 W/cm2. A power-law relationship IPL approximately equals P(gamma ) was obtained between PL intensity and the excitation power. PL mechanism for TiO2 nanocrystals is attributed to the recombination via the localized levels within the forbidden gap of defect-related centers, which reside in the surface region of TiO2 nanocrystals.
Raman spectroscopy was examined for ester ferroelectric liquid crystal D-4-(2-methylbutoxy)phenyl 4-decyloxybenzoate (MBOPDOB) to study configuration between s-cis and s-trans isomers and phase transitions between adjacent phases. Temperature behaviors were investigated for three low- frequency Raman modes at 15, 49 and 93 cm-1. The 15 and 49 cm-1 Raman lines vanish at crystal-Sm C* point and their temperature-cycle measurement gives 4 degree(s)C width of thermal hysteresis from crystal to Sm C*, which indicates first-order transition. Quasielastic scattering near the crystal-Sm C* point below 30 cm-1 shows a critical slowing-down phenomenon relative to a long orientational relaxation in the Sm C* phase. The second-order property of the Sm C*-Sm A transition were proved by the facts that the 93 cm-1 Raman line and spontaneous polarization go smoothly through the point, in addition a very small heat of the transition was recorded. Two conformations of COO group characterized by C equals O stretch mode at 1708 cm-1 and C-O-C asymmetric stretch at 1177 cm-1, the S-trans and s-cis isomers were found to coexist in the crystal phase. The S-trans isomer are transformed to the S-cis during the crystal-Sm C* transition and in the Sm A and isotropic phases. The larger dipole of the S-cis conformer is in favor of the formation of the ferroelectric phase.
The waveguiding epitaxial LiTaO3 and LiNbO3 films have been prepared on sapphire substrates by pulsed laser deposition technique. The as-grown films were characterized by Raman scattering, XRD and SEM techniques, which revealed that epitaxial LiTaO3 and LiNbO3 films with small roughness were achieved on (001) and (012) sapphire substrates, respectively. Optical waveguiding properties were demonstrated by m-line measurement of TM and TE modes.
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