Photonic properties and applications of glass micro- and nanospheres

Fabrication, morphological and spectroscopic assessment of micro- and nano-spheres are reported. Spheres with size ranging from few hundreds of nm to few hundreds of m have been prepared by different methods, i.e. sol-gel, melting and core-shell techniques. Pure and rare-earth-doped spheres find their major applications as microsensors and microlasers, respectively. We refer here to Erbium-activated systems only: (i) coated micro spheres where the silica core, obtained by telecom fiber melting, is coated with an Er3+-70SiO2-30HfO2 film; (ii) Er3+-activated microspheres obtained from silicate-modified glasses and phosphate glasses using a plasma torch; (iii) sol-gel Er3+-doped silica micro- and nano-spheres. The whispering gallery mode spectra were analysed as a function of sphere diameter, thickness of coating (if any) and Erbium content. Photoluminescence spectra of different systems gave interesting indications on the potential of some activated microspheres for lasing applications. For instance, sol-gel Er3+-activated core-shell-like structures exhibited a lifetime of 12.8 ms, leading to a quantum efficiency (QE) of 71%. Even higher QE (76%) was estimated in sol-gel Er3+-silica spheres.