Yb-doped silica preform precursor nanoparticles and the photodarkening in them

A series of Yb-doped silica-based nanoparticles were fabricated in the MCVD process. Their compositions and doping levels were well controlled from 0 to 0.53 wt% for Yb and from 0 to 2.1 wt% for Al. The nanoparticles are of about 21.3 ± 4.6 nm in size, but their sizes and NIR absorption are influenced by the Al concentration. At a fixed Al doping level, the NIR absorption depends on the Yb concentration. The nanoparticles exhibit a strong composition dependence of the photodarkening induced by the X-ray irradiation.