The diffusion of P in P2O5–SiO2 glass was investigated by annealing of doped layers on the inner surface of quartz glass tubes between 1700 and 2000C and measuring radial phosphorus profiles by X-ray microprobe analysis and refractive index profiling, respectively, subsequent to the tube collapse. By comparison with calculated profiles, diffusion coefficients could be determined, which were fitted by an Arrhenius function, where the pre-exponential D0 = 10−0.18cm2/s was constant but the activation energy decreased with increasing concentration as E = (454–56c0.32)kJ/molK, valid for a concentration range, c, between 0.04 and 10mol%P2O5. The diffusion resembled that earlier determined for Al in SiO2 glass, but with smaller diffusivities and activation energies.

Diffusion of Phosphorus-Doped Silica for Active Optical Fibers. J.Kirchhof, S.Unger, J.Dellith: Journal of Non-Crystalline Solids, 2004, 345-346, 234-8