DFT+U Study of Fe-Doping Enhanced Random Lasing in ZnO Nanorods: Quantum Confinement and Vacancy Effects

Abstract

This paper aims to evaluate how Fe-doped ZnO nanorods with controlled oxygen-vacancy levels can improve random lasing performance for photonic applications. An investigation of the electronic structure, defect dynamics, and optical properties of these nanostructures is accomplished through density functional theory (DFT+U) calculations. Specifically, it has been reported that the incorporation of about 3 at.% Fe can introduce intermediate 3d energy levels in the ZnO bandgap, suggesting the possibility of carrier population inversion and an estimated reduction of the lasing threshold by approximately 30–40% for Fe-doped ZnO nanorods compared to undoped nanorods, under idealized theoretical assumptions. It is also determined that oxygen vacancies act as scattering centers, altering the local electromagnetic environment around the ZnO nanorods and thereby optimizing the gain. Additionally, quantum confinement is predicted to dominate the emission from ZnO nanorods with diameters below 4 nm, thereby shifting the emission spectrum to higher energy (i.e., a blue shift) and increasing the nanorods' oscillator strength. Therefore, it is fair to anticipate that optimum random lasing would occur in ZnO nanorods having diameters of 3-4 nm, doped at 2-3 at.% Fe, and synthesized in oxygen-deficient environments. Although all computations in this study have made assumptions about the configuration of defect sites and the degree of oxidation of ZnO nanorod surfaces, these theoretical results may help to develop the next-generation materials for a range of applications, including biosensing, imaging, and photonics.