A theoretical study of the absorption spectra of Pb+ and Pb3+ in site K+ of microcline:: application to the color of amazonite

The blue-green color of amazonite has been assigned by various authors to ions Pb+ (6 s)(2) (6 p) and/or Pb3+ (6 s) in site of KC of microcline. Owing to the complex which forms between the ion Pb3+ and the lone pairs of the oxygen atoms surrounding it, the peripheral electron of Pb3+ passes on the levels (6 p) of the latter, which results in a great similarity of the spectra of Pb+ and Pb3+ in amazonite (the transition energies are multiplied by a factor greater than 1), whereas, in the isolated state, these spectra are completely different from one another. An analytical development of the crystal field around a site K+ is established. Under the effect of the crystal field, the transition P-2(1/2)-->P-2(3/2) (6 p) is split into two double transitions. The lower transition only falls in the visible domain (1.6-1.8 eV for Pb+), the second in U-V. The green color would arise from the ion Pb+, whereas the blue one would be attributed to the ion Pb3+.