The photochromic and photorefractive response of Czochralski-grown bismuth(12) germanium oxygen(20) doped with chromium and manganese

Scope and method of study. The optical properties of Czochralski grown Bi12GeO20, BGO, doped with chromium and manganese were studied using absorption spectroscopy, the photochromic effect, and the photorefractive effect. The wavelengths responsible for the photochromic effect were determined along with the thermal stability of the photochromic effect. Holographic index gratings were also written using the photorefractive effect. The thermal and optical stability of these gratings were investigated.; Findings and conclusions. The addition of chromium causes strong absorption starting in the IR and continuing on throughout the visible to the band gap. This, strong absorption is due to Cr4+ (d 2). Cr5+ (d1) is also present. When UV and visible light is incident on BGO:Cr, an increase in the absorption coefficient is observed. The light excites an electron from the anti-site bismuth to Cr5+ creating more Cr4+, which increases the absorption coefficient. This is stable up to ∼425 K.; The addition of manganese causes very weak absorption beginning in the in the IR and continuing on into the visible. This weak absorption is due to Mn3+ (d4). Mn2+ (d 5) is also present. Shining UV and visible light on BGO:Mn eliminates the weak absorption and increases the absorption shoulder. The light excites an electron from the anti-site bismuth to Mn3+ creating more Mn2+. The increased absorption shoulder is stable up to ∼425 K.; Photorefractive gratings were written in BGO:Cr and BGO:Mn. The addition of chromium and manganese slows down the speed of grating formation but the gratings are nearly permanent at room temperature. The decrease in the speed of grating formation is most likely due to a decrease in the mobility. The gratings are nearly permanent because, chromium and manganese introduce deep traps into BGO. The gratings are stable up to ∼425 K, matching the decay of the photochromic effect.