Towards controllable optical properties of silicon based nanoparticles for applications in opto-electronics

Size-dependent optical properties of laser-synthesized Si-based nanopowders were investigated by photo-luminescence (PL) and photo-luminescence excitation (PLE) spectroscopy on powder samples annealed in air in the 700–1000 °C temperature range. TEM analysis reveals that at increasing annealing temperature a progressive Si nanoparticle size reduction occurs as a consequence of crystalline core oxidation, and a corresponding blue-shift of the PL emission is observed. The subsequent step is the preparation of nanocomposite materials by nanopowders dispersion and integration into a continuous silica phase by sol–gel processing. Synthesis parameters are adjusted in order to preserve the PL red emission from Si nanostructures. An interesting application would consist in the Er incorporation into the nanocomposite glassy material aiming at the 1.54 μm Er emission sensitization by energy transfer from Si nanostructures to nearby Er ions. However, it was found that Si nanoparticles are completely oxidized at the processing temperatures (1400 °C) required to activate Er emission. Here we demonstrate that better and promising results can be achieved introducing in the sol–gel Si-based nanopowders withstanding higher temperatures.