Wide transparency range and high refractive index lead-niobium-germanate glass thin films

Abstract

Lead-niobium-germanate glass thin films have been produced by pulsed laser deposition in a broad O2 pressure range (10-6-10 -1 mbar). The cation composition in the films approaches that of the glass target for a pressure of 10-2 mbar. The oxygen content is only close to or above that of the glass for a pressure close to 10-1 mbar, for which a Pb enrichment is also observed. Films grown in vacuum are highly absorbing, whereas transparent films with an absorption edge shifted to the UV with respect to the bulk glass are produced for pressures higher than 10-2 mbar. The evolution of the optical energy gap and the refractive index of the films with the oxygen pressure is correlated to the changes observed in the film composition and discussed in terms of the features of the deposition process, the role of oxygen in the formation of the glass network and the progressive increase of the oxidation state of the cations as the oxygen pressure is increased.