Evidence for two-path recombination of photoinduced small polarons in reduced LiNbO3

Abstract

The recombination of photoinduced free Nb-Nb(4+) and bound Nb-Li(4+) small polarons to NbLi4+NbNb4+ bipolarons is investigated in nominally pure, reduced LiNbO3 single crystals by means of excited-state-absorption spectroscopy. We discovered a two-component decay of the light-induced absorption alpha(li)(t) for probe light at lambda=785 nm and moderate pump beam intensities (I-p << 670 GW/m(2)). These experimental results give strong evidence for the existence of a two-path recombination of the photoinduced polarons. A corresponding model taking into account hopping charge transport and trapping is presented.