Photochromic response of bismuth germanium oxide doped with chromium

Citation
Js. Mccullough et al., Photochromic response of bismuth germanium oxide doped with chromium, J APPL PHYS, 90(12), 2001, pp. 6017-6021
Citations number
27
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF APPLIED PHYSICS
ISSN journal
00218979 → ACNP
Volume
90
Issue
12
Year of publication
2001
Pages
6017 - 6021
Database
ISI
SICI code
0021-8979(200112)90:12<6017:PROBGO>2.0.ZU;2-3
Abstract
Doping the photorefractive material bismuth germanium oxide Bi12GeO20(BGO) with chromium significantly affects its optical properties. An absorption s pectrum taken at 300 K shows that the introduction of chromium produces a s trong unresolved band which overlaps the absorption cutoff of BGO and a ser ies of smaller overlapping bands between 650 and 1100 nm. Cooling BGO:Cr to 10 K sharpens the small bands and resolves the strong band into a peak nea r 510 nm. This peak is responsible for the reddish-brown color of BGO:Cr. E xcitation at room temperature with visible light increases the bands in the 650-1100 nm range. The production of this additional room temperature phot ochromic absorption is most efficient with excitation near 490 nm but exten ds throughout the visible. Chromium occupies the tetrahedral germanium site in BGO; and the observed spectra are consistent with a Cr4+ tetrahedral st ate. During crystal growth some of the chromium gives up an electron to the antisite bismuth native defect and becomes Cr5+. Exposing the sample to li ght returns the electron to the chromium and increases the Cr4+ absorption. The photoinduced absorption is thermally stable for temperatures up to abo ut 425 K. This stability suggests that doping BGO with Cr should lead to ro om temperature persistent photorefractive gratings. (C) 2001 American Insti tute of Physics.