Controlled growth of SnO₂ nanocrystals in Eu³⁺-Doped SiO₂-SnO₂ planar waveguides: a spectroscopic investigation

We report on the fabrication of Eu³⁺-doped SiO₂−SnO₂ low-loss (0.8 dB/cm at 632.8 nm) glass-ceramic planar waveguides, fabricated by the sol−gel technique and dip-coating processing. The effects of heat treatments on the growth and evolution of SnO₂ nanocrystals in the matrix were investigated using different spectroscopic tools. In situ high-temperature X-ray diffraction allowed for the determination of the crystallization temperature and confirmed the formation of tetragonal rutile SnO₂ crystals. The effect of crystallization on the optical properties and on the photoluminescence of Eu³⁺ ions was also studied. Low-frequency Raman scattering was successfully used to determine the crystal size, and the results obtained were found to be consistent with transmission electron microscopy measurements. The breakage of Si−O−Sn linkages during the formation of SnO₂ nanocrystals in the matrix was investigated by Fourier-transform infrared spectroscopy.