Exposing the photorefractive bismuth germanium oxide (BGO) at low temperatures to 2.5-3.3 eV light produces photochromic absorption bands. In both undoped and Fe-doped material the absorption consists of overlapping bands at 1.5, 2.2, 2.7, and 3.1 eV. The 1.5- and 2.2-eV components are relatively weaker in Fe-doped BGO. In undoped BGO the photochromic bands anneal together above 200 K. Doping with iron adds an anneal stage in the 110-200 K range that matches the recovery of Fe3+. Optical bleaching with 1.5-eV light was much less efficient than with visible band light. Thus, the 1.5-eV photochromic band may be an internal transition of the center responsible for the 2.2-eV band. In BGO:Al the aluminum electronically compensates the deep donor center responsible for the yellow coloration observed in undoped crystals. Photoexcitation at 9 K produces overlapping absorption bands at 1, 1.38, and 2.45 eV. All three bands have major anneal stage in the 80-100 K range. They also bleach out together when the sample is exposed to either infrared or visible range light. The [AlO4]0 center which causes the coloration observed in smoky quartz is a plausible model for the visible range photochromic center in BGO:Al.
ASJC Scopus subject areas
- Physics and Astronomy(all)