Effects of fluorine on the properties of Yb/Ce co-doped aluminosilicate preforms prepared by MCVD with organic chelate precursor doping technique

Abstract Co-doped Yb/Ce aluminosilicate fiber preforms with less than 1 Wt% fluorine were prepared by MCVD with organic chelate precursor doping technique at 1400 °C. Fluorine content characterized by electron probe microanalysis decreased with increasing SiF 4 flow and flow ratio of SiF 4 /SiCl 4 . Under maximum SiF 4 flow the concentrations of Yb 2 O 3 and CeO 2 in the perform core were only as much as 17% and 25% under minimum SiF 4 flow, respectively, but smaller refractive index change was only shown in fiber core. The reason was that the reaction of SiF 4 with Al 2 O 3 ,Yb 2 O 3 ,CeO 2 were intensified with increasing flow ratio of SiF 4 /SiCl 4 and then resulted in producing more exhaust gas such as AlF 3 , YbF 3 and CeF 4 . Raman spectra of core glasses with − 1 of Si F stretching bond was not observed, and with growth of fluorine content antisymmetric stretching vibrations of Si-O-Si linkages split from an envelope of 1188 cm − 1 into two peaks or three peaks shifted higher frequency. At the same time, Boson peak near 125 cm − 1 shifted to lower frequency. They were attributed to some minor changes of glass's network structure due to introducing lower fluorine into core glasses. On base of bonding energy measured by X-ray photoelectric spectroscopy, the plane graph describing the complex bonding distribution with F in core was supplied to in order to illustrate network structure change.