YbPO4 nano-cylinders formation and alignment within optical fiber preforms using fiber-drawing process

Abstract

This paper describes the first synthesis of YbPO4 nano-cylinders and nanoparticles within optical fiber preforms. To obtain YbPO4-doped silica monoliths, phosphosilicate powders, previously prepared by a sol–gel method, were impregnated with a solution containing an ytterbium salt. Then, they were compressed into cylinders and sintered at high temperature. These doped monoliths were densified under controlled atmosphere and then drawn at high temperature into 1.6mm diameter-rods. The composition, structural and optical properties of these monoliths and rods were investigated using Electron Probe Micro-Analysis, Transmission Electron Microscopy (TEM), Raman spectroscopy and IR absorption measurements. The size of the YbPO4 nanoparticles within the monoliths were found to be in the range of 8–15nm and 13–25nm, depending on the Yb-doping amount. Upon drawing the most concentrated Yb-doped monoliths into rods, the nanoparticles evolve to form nano-cylinders with a mean diameter around 40nm and a length of about 400nm. Similar behavior was observed for the less concentrated Yb-doped monoliths, once drawn into rods but a lower number of nano-cylinders were found in this case. Structural analysis, based on Raman spectroscopy and TEM experiments, shows that all these nano-objects have a tetragonal xenotime structure (I41/amd). Moreover, it was found that the nano-cylinders were all aligned parallel to the drawing direction. These SiO2-P2O5:YbPO4 glass ceramics exhibit a structured absorption spectra around 980nm, which corroborates the Yb3+crystalline environment.