Photonic properties and applications of glass micro- and nanospheres
Résumé
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 μm 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 micro-sensors and micro-lasers, respectively. We refer here to Erbium-activated systems only: (i) coated micro spheres where the silica core, obtained by telecom fibre melting, is coated with an Er3+–70SiO2–30HfO2 film; (ii) Er3+-activated micro-spheres 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 micro-spheres 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.