LOW-TEMPERATURE PHOTOCHROMIC RESPONSE OF PHOSPHORUS-DOPED BISMUTH SILICON-OXIDE

Phosphorus is one of several dopants that electronically compensate th e native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measur ements of a series of Czochralski-grown P-doped BSO crystals show that similar to 0.1-0.15 at. % P is needed in the sample to fully remove t he yellow coloration. The absorption cutoff in the fully compensated P -doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10-15 K with near band-edge light pr oduces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undo ped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker abso rption in the blue-green. By comparison with the spectra observed in u ndoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4](-) center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4](0) center. (C) 1995 American Institute of Physics.