Enhanced effect of electron-hole plasma emission in Dy, Li codoped ZnO nanostructures

Pink branched $Dy3+$ and $Li+$ codoped ZnO nanowires were synthesized by simply annealing the polymeric precursor. For the undoped sample, electrons at the bottom of the conductor band return to the ground state via a process of free exciton and defect intermediate level, and subsequently emit 3.2 and 2.4 eV photons. Furthermore, their intensities both increase while their positions are almost invariant with increasing excitation intensity. For the doped nanostructure, compositional inhomogeneity results in localization of nonequilibrium carriers and enhances the photoluminescence performance. The near-band edge emission shows higher emission efficiency and is dominated by the transition of free electrons to free holes. Moreover, it also exhibits a power-dependent redshift and a broader and more asymmetric line shape on its lower-energy side with increasing excitation intensity. For the green emission in codoping ZnO nanostructures, the formation of deeper traps from the complexes of defects and impurities results into a redshift to 523 nm. Additionally, its position remains invariant with increasing excitation intensity. It is proposed that the charge compensation, surface passivation, and carrier delocalization lead to the fully suppressed green emission at higher excitation intensity.