TiO(2) colloidal nanoparticles and nanocrystals are prepared by hydrolysis of titanium isopropoxide employing a surfactant-free synthetic hydrothermal method. The synthesized samples are characterized by X-ray diffraction (XRD), HRTEM and FTIR. The XRD study confirms that the size of the colloidal nanoparticle is around 4 nm which the HRTEM analysis indicates the sizes of the colloidal nanoparticles are in the range of 2.5 nm. The fluorescence property of the TiO(2) colloidal nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. We have observed new emission bands at 387 nm,421 nm, 485 nm, 530 nm and 574 nm wavelengths, first one (387 nm) being emission due to annihilation of excitons while remaining four could be arising from surface states. The emission spectrum of annealed nanocrystallites is also having these four band emissions. It is observed that the surface state emission basically consists of two categories of emission.

Silver nano-colloid was prepared by chemical reduction method and its nonlinear absorption properties were investigated by using open aperture z-scan experiment with nanosecond laser pulses operating at 532 nm. Interestingly, a switch over from saturable absorption to reverse saturable absorption was observed when the input intensity is increased from 28.1 to 175.8 MW/cm 2 . The underlying mechanism responsible for the observed switching behaviour is the interplay between ground state plasmon band bleaching and excited state absorption. Theoretical fitting was done by using a model in which nonlinear absorption coefficient as well as saturation intensity are incorporated.

Silver/titanium dioxide nanoparticles with varied concentration of silver have been synthesized by a simple laser light induced chemical reaction, where bulk titanium dioxide powder is used as the starting material. The particle size, morphology, crystal structure, and optical properties were characterized by transmission electron microscopy, x-ray diffraction, UV-Vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The x-ray diffraction pattern revealed that the TiO2 nanoparticles obtained are in pure rutile phase. The important observation from transmission electron microscopic images is that the Ag particles are distributed over the surface of titanium dioxide nanoparticles. The band gap of the TiO2 nanoparticles was tuned between 1.75 and 2.75 eV by varying Ag concentration. The nonlinear optical absorption and optical limiting performance of Ag:TiO2 nanocomposites were investigated by open aperture z-scan using nanosecond Nd:YAG laser pulses operating at 532 nm. The best optical limiting threshold obtained was 113MW/cm2.

Keywords:Mode-matched thermal lens Metallic-dye nanocluster Thermal diffusivity a b s t r a c t Dual beam mode-matched thermal lens method has been employed to measure the heat diffusion in nanofluid of silver with various volumes of rhodamine 6G, both dispersed in water. The important observation is an indication of temperature dependent diffusivity and that the overall heat diffusion is slower in the chemically prepared Ag sol compared to that of water. The experimental results can be explained assuming that Brownian motion is the main mechanism of heat transfer under the present experimental conditions. Light induced aggregation of the nanoparticles can also result in an anomalous diffusion behavior.

A solid-state laser based on a dye-doped deoxyribonucleic acid (DNA) matrix is described. A thin solid film of DNA has been fabricated by treating with polyvinyl alcohol (PVA) and used as a host for the laser dye Rhodamine 6G. The edge emitted spectrum clearly indicated the existence of laser modes and amplified spontaneous emission. Lasing was obtained by pumping with a frequency-doubled Nd:YAG laser at 532 nm. For a pump energy of 10 mJ/pulse, an intense line with FWHM approximately 0.2 nm was observed at 566 nm due to selective mode excitation.