  For erbium-doped amorphous oxides, such as those that are used in compact
lightwave devices interfaced with silicon, values of the refractive indices are
commonly obtained empirically. This work, combining experimental and
theoretical studies, examines silica as the exemplary host and the influence of
erbium doping on the refractive index. Analysis of data is presented for the
spectral refractive index in the ultraviolet to near infrared wavelength range
of heavily erbium-doped silica thin films prepared by spin coating a sol-gel
precursor on silicon and subsequent vacuum annealing. Effective medium
Lorentz-Lorenz data analysis determines that the dopant component has a
refractive index of 1.76(0.24) with wavelength dispersion constrained to within
2 percent. Considering the dopant as a localized ErO6 impurity complex, a
corresponding theoretical refractive index of 1.662 is derived by calculating
the optical polarizability and volume of the impurity. Data presented for
room-temperature (293 K) photoluminescence in the vicinity of 1.54 micron are
shown to be consistent with random variability in impurity sites. Inherent
advantages of studying colloid-based materials are discussed. To the best of
the authors knowledge, such a detailed study of the refractive index associated
with erbium impurities in silica is being reported for the first time in the
literature.
