Photorefractive behavior of strontium barium niobate doped with trivalent rare-earths

This paper investigated the spectroscopy and photorefractive response of SBN doped with Ce3+, Pr3+ and Nd3+. Ce3+ shows a broad absorption extending from the band edge at about 3.2 eV (380 nm) to around 600 nm. This is assigned to a combination of 4f-5d and charge transfer absorption. In contrast, the spectrum of Pr3+ and Nd3+ consists of a number of sharp f-f absorption lines, together with a weak background, which may be due to other impurities or defects. In addition these ions have metastable excited states with lifetimes of about 100 μs. Ce3+-doped SBN shows a high photorefractive sensitivity (Sn2) of 9.5 × 10-3 cm2/J due to one-photon ionization. In Pr and Nd the one-photon response is much lower. Identification of the contribution from the trivalent rare-earth itself is complicated by the presence of a strong background. It is proposed that at least some of this background arises from niobium reduction resulting from the charge compensating response of the host.