Kinetics of light‐induced polaron‐ and VIS‐centers in SBN:Ce single crystals at low temperature

Abstract

The promising photorefractive crystal Sr x Ba 1-x Nb 2 O 6 (SBN, congruent composition x=0.61) can be doped with polyvalent ions like Ce to enhance photorefractive properties. Illumination with blue Ar + -laser light at low temperature creates light-induced NIR and VIS absorption bands. The NIR absorption has been identified as being due to Nb 4+ electron polarons and their properties have been investigated in some detail. The VIS-Centers are less well understood and their nature is still under discussion. It has been shown by our previous measurements that illumination with red Kr + -laser light (647 nm) or red laser diodes (673 nm) leads to a dissociation of the VIS-Centers and a simultaneous build-up of a transient NIR-polaron absorption. We report here some new facts important for the simplified charge transfer model needed to describe quantitatively the equilibrium values and the dynamics of the NIR-polaron and VIS-center absorption. These features give new insight into the dynamic nature of these VIS-centers, which are currently being discussed as either bipolarons (in analogy to LiNbO 3 ) or polarons trapped at charged centers, or charge transfer vibronic exitons (CTVEs) being trapped at charged centers.

Stable Color Centers Induced in Pure and Neodymium Doped Ca0.28Ba0.72Nb2O6Crystals by Gamma Irradiation

“…This absorption is very similar to the absorption induced in SBN:Ce crystals under visible light illumination [12]. In spite of the fact that this absorption has higher temperature stability in comparison with the absorption around 7000 cm −1 , its value goes to zero at room temperature [12]. The obtained absorption bands are relatively wide and most likely they could be represented as superposition of several overlapping bands belonging for dierent centers.…”

“…In accordance with Refs. [6,12,13], the Nb 4+ polarons absorption in TBS and related crystals is observed around 60007000 cm −1 and is stable only at low temperatures. In such a way it should not be observed in our experiment.…”