Er3+-activated silica inverse opals synthesized by the sol-gel method

We present the details of the sol gel processing used to realize inverse silica opal, where the silica was activated with 0.3 mol% of Er3+ ions. The template (direct opal) was obtained assembling polystyrene spheres of the dimensions of 260 nm by means of a vertical deposition technique. The Er3+-activated silica inverse opal was obtained infiltrating, into the void of the template, the silica sol doped with Er3+ ions and subsequently removing the polystyrene spheres by means of calcinations. Scanning electron microscope showed that the inverse opals possess a fcc structure with a air hollows of about 210 nm and a photonic band gap, in the visible range, was observed from reflectance measurements. Spectroscopic properties of Er3+- activated silica inverse opal were investigated by luminescence spectroscopy, where, upon excitation at 514.5 nm, an emission of 4I13/2 ® 4I15/2 of Er3+ ions transition with a 21 nm bandwidth was observed. Moreover the 4I13/2 level decay curve presents a single-exponential profile, with a measured lifetime of 18 ms, corresponding a high quantum efficiency of the system.