Three-photon-induced luminescence of gold nanoparticles embedded in and located on the surface of glassy nanolayers

We report on the multiphoton-induced luminescence of gold nanoparticles embedded in thin glassy silicate-titanate films. The glassy layers doped with gold( III) chloride are synthesized by a sol-gel coating process. Gold nanoparticles are generated by subsequent annealing of the thin films at 300 degrees C. Intensive near-infrared femtosecond laser irradiation also initiates the formation of gold particles, providing the possibility of spatially resolved photoactivation of the film. The reduction of gold ions to gold nanoparticles is monitored by Au L-3-edge x-ray absorption near edge spectroscopy ( XANES), UV-vis absorption spectroscopy, scanning electron microscopy ( SEM) and transmission electron microscopy ( TEM). The particle sizes and shapes can be tuned by changing the metal concentration in the matrix. We demonstrate that the particles exhibit an efficient, long time stable, white luminescence during near-infrared Ti: sapphire femtosecond laser excitation. The laser power-emission intensity law indicates that the luminescence is induced by the absorption of three laser photons. Cross-sectional TEM images show that gold nanoparticles are both embedded in the glassy matrix and located on the film surface. Hence, the particles should be accessible for viable applications, for example as sensor materials, and could therefore become a powerful alternative to organic and semiconducting fluorophores in biological imaging.