Identification and origin of visible transitions in one dimensional (1D) ZnO nanostructures: Excitation wavelength and morphology dependence study

Abstract

In this present work, one dimensional (1D) ZnO nanostructures were synthesized by mechanical assisted thermal decomposition process. The samples were characterized by transmission electron microscopy (TEM) for morphology, high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) for structural characterization. Photoluminescence (PL) and Photoluminescence spectra evolution was studied as a function of (i) excitation wavelength (λEx: 310–370nm) and (ii) morphology (nanoneedles and nanorods). PL spectra were observed to be highly asymmetric with strong dependence on excitation wavelength (λEx). PL spectra categorized into two types as a function of excitation wavelength (λEx): I. λEx≤345nm and II. λEx≥350nm.The PL spectra were deconvoluted into multiple Gaussian components for each excitation wavelength. The position of each component is a signature of its origin and corresponds to specific visible transition. The transition involving origin from conduction band (CB) are absent for excitation wavelength λEx≥350nm. The tunable photoresponse is achieved in 1D ZnO nanostructures by varying (i) excitation wavelength and (ii) morphology: nanoneedles to nanorods. PL intensity increases as aspect ratio decrease from nanoneedles to nanorods morphology. This is attributed to non-radiative quenching by near surface defects.