Lead Contamination of Flux-Grown Garnets and the Effect on Optical Properties

Abstract

One occasionally observes in flux‐grown gallium and aluminum garnets a purple discoloration. Combined optical absorption, emission spectrographic and electron microprobe studies of crystals showing pronounced color banding indicate a direct correlation between depth of purple color and dissolved lead content. In addition to the broad visible absorption band leading to the purple color, a sharp absorption band is observed near 2.8 μ in the discolored crystals. Since the small lead impurity cannot by itself produce either of these absorptions, they must be attributed to associated charge‐compensating mechanism—e.g., charged vacancies (color centers) in the one instance and OH⁻ replacements for oxygen ions in the other. While it can be argued that the lead impurity must be partially self‐compensating, the divalent state appears to predominate.