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An aluminophosphate glass system containing silver and tin was prepared by the melt-quenching technique in which spherical silver nanoparticles (NPs) of different sizes were embedded upon heat treatment. Optical absorption was used in the assessment of particle growth and for particle size estimation yielding mean radii in the 10-40 nm range. Measurements in the UV region revealed absorption features indicative of the occurrence of silver ions and twofold-coordinated tin centers. Photoluminescence spectroscopy excited at 355 nm showed a broadband emission around 420 nm for the non-heat-treated glass, which shows a thermal quenching effect in temperature dependence measurements. Heat-treated glass shows a dip in the emission spectrum ascribed to absorption by NPs. The luminescence is attributed to single Ag + ions. The nature of the silver emitting states is discussed.

The nonequilibrium carrier dynamics in Ag nanoparticles was explored by femtosecond optical pump-probe spectroscopy. Metal-dielectric nanocomposite materials containing Ag nanoparticles of different sizes were prepared by thermal treatment of aluminophosphate glasses. The ultrafast relaxation dynamics of the electron scattering on the 10 À13 -10 À12 sec scale shows sizeand pump power-dependent properties. The two-photon absorption process in nanoparticles of different sizes is discussed. The laser-induced coherent vibrations of nanoparticles were observed in transient transmission experiments.

Light-induced insulator-to-metal phase transition of vanadium dioxide films was studied by ultrafast optical pump-probe spectroscopy. The transient optical reflection measurement shows that both heating and laser illumination contribute to the phase transition of VO 2 . Within 10 À11 -10 À9 sec, these two mechanisms are competitive. Excited-state dynamics were found to be strongly dependent on the concentration of structural defects and the pump laser power as well. Comparison of the transient reflection of VO 2 films deposited on different substrates suggests that the excitonic-controlled lightinduced insulator-to-metal phase transition in VO 2 proceeded through an intermediate state. The transient reflection measurement of VO 2 in metallic phase shows a three-stage relaxation process. A polaron excitation model is introduced to describe the dynamical process for metallic VO 2 .

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