Electron transfer and intershell spectroscopic parameters of Pb 2+: Changes when lead halide films interact with alkali halide substrates

Abstract

UV spectral data for Pb 2+ highly diluted in alkali halide crystals and in lead halide thin films are shown to be consistent in the context of current inorganic spectroscopy. For Pb 2+ in (i) alkali halides and (ii) lead halides the optical electronegativities are 1.2 and 1.4 respectively, while for the 1S 0→ 3P 1 frequency ( v s−p) relationship ( v s−p = v f− v f mh where h is the nephelauxetic parameter of the complexing halide ion), the values of v f are 60 700 cm -1 and 64 400 cm -1 and the values of m are 0.20 and 0.22 respectively. The results indicate that the modified Pb 2+ ion model used for Pb 2+ ions in alkali halide crystals can be extended to Pb 2+ halide salts. These rationalizations indicate the usefulness of UV spectroscopic measurements for studying the penetration of lead halide thin films into crystalline alkali halides. Spectral changes occuring when sandwiches of lead halide films between NaCl and KBr substrates are maintained at 300°C indicate substantial evaporation of the lead halide film and preference of Pb 2+ to diffuse into KBr rather than into NaCl.