Study of optical transitions in an individual ZnO tetrapod using two-photon photoluminescence excitation spectrum

Abstract

Two-photon excited photoluminescence (PL) measurements have been carried out on an individual ZnO tetrapod at low temperature (8 K) using femtosecond laser pulses in the wavelength range of 714-850 nm. Simultaneously PL and second-harmonic generation were observed. The integrated PL intensity excitation spectrum at different two-photon excitation frequencies has eight peaks, which are in good correspondence to the exciton-phonon complexes L 1b , L 1a , and the free exciton lines B n=3, A n=3, B n=2, A n=2, B n=1, and A n=1 seen in ZnO film. This technique can be used to measure the optical transitions in individual nanostructures, which is very difficult to achieve using the traditional transmission/reflection method. © 2009 Springer-Verlag.