COMPARISONS OF TIN DEPTH PROFILE ANALYSIS IN FLOAT GLASS

Data are presented showing the profile of tin diffusion during the pro duction of float glass, by measuring non-destructively the refractive index profiles in the diffused layer. The optical waveguide modes give unequivocal evidence for an anomaly in the tin depth distribution. Th e results are compared with those from sectioning techniques, used in depth profiles determined by ion beam analyses and cathodoluminescence (CL). There is agreement between these methods which confirm the pres ence of a maximum in the tin concentration below the surface which had been in contact with the tin bath (this had been linked by Mossbauer data to a rise in the Sn4+ concentration). The ion beam analyses recor d different depth profiles for Si, Na and Ca. The Sn4+ feature increas es the refractive index, as does the diffusion of Sn2+. The index beco mes constant at large tin concentrations. We suggest that Sn4+ is link ed to CL emission at 2.68 eV and Sn2+ to the 1.97 eV CL emission. Iron impurities give a 1.73 eV signal. Contrary to earlier suggestions, we prc,pose that the luminescence associated with the presence of tin ar ises from intrinsic defects stabilised by the tin, not from tin acting directly as a luminescence site. (C) 1998 Elsevier Science B.V.