Optical alignment of the exciton in ZnO nanoparticles

The exciton spin dynamics of zinc oxide nanoparticles (NPs) of sizes ranging from 2.3 to 6.6 nm has been studied by time-resolved photoluminescence. Following a quasiresonant linearly polarized excitation, the exciton photoluminescence of an ensemble of NPs exhibits a linear polarization of 15%, demonstrating the optical alignment of exciton in zinc oxide NPs. Within the accuracy of our experimental setup, no decay time of the linear polarization is observed on the exciton lifetime scale, reflecting an exciton spin relaxation time longer than 1 ns. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3504252]