Impurity and morphological dependence on photoluminescence and enhanced impurity-induced two-photon absorption in ZnO

In this study, we characterize the relative crystal quality of zinc oxide (ZnO) synthesized at various temperatures via photoluminescence (PL) measurements. By varying the oxidation temperature during the growth process, different sample morphologies arise. These structural differences cause changes in the PL spectra which allow us to gain insight into the crystal purity. We employ three independent spectroscopic methods to examine ZnO prepared with various morphologies; time-integrated PL, random lasing, and time-resolved PL. As a result of the impurity band being resonant with the two-photon absorption (2PA) range, multifold enhanced 2PA is observed and the 2PA coefficient is measured to be 2500 cm/GW for tetrapod ZnO at 613 nm.