Lifetime of small polarons in strontium-barium-niobate single crystals doped with cerium or chromium

Small polarons are excited by pulsed illumination (lambda =532 nm) of stron tium-barium-niobate single crystals doped with 0.66 mol % cerium or with 0. 025 mol % chromium. The dark decay of the polarons is observed by monitorin g the light-induced absorption at lambda =632.8 nm and at lambda =785 nm. T he relaxation fulfills a stretched-exponential behavior over at least five decades. Using the Arrhenius law the temperature dependence yields the acti vation energy E-A=(0.58 +/-0.02) eV and a frequency factor of Z=(5 +/-3)x10 (13) s(-1). Delayed double-pulse technique (lambda =532 nm pulse followed b y a lambda =1064 nm pulse) reveals a distance dependent recombination rate of the small polarons, i.e., the lifetime of a created polaron is a functio n of the distance to the next available deep electron trap. In SBN:Cr the R branch can be excited by pulses of lambda =1064 nm with energy transfer vi a an unknown X center. Excitation and recombination show a single-exponenti al temporal evolution without any significant temperature dependence. (C) 2 001 American Institute of Physics.