Excitation induced enhancement of spectral response and energy transfer mechanisms in Fe/Sm modified ZnO phosphors

Abstract

The present study aims to analyze the tunability of photonic emissions as a function of excitation wavelengths in Fe/Sm co-doped ZnO phosphors. We have investigated the up-conversion (UC) and down-conversion (DC) luminescences in detail along with possible channels for energy transfer and their local electronic structures. These phosphors are polycrystalline with a hexagonal wurtzite structure, and the co-doping of Fe/Sm ions leads the 3D-pyramid like morphology of the ZnO to transform in flower-shaped nanorods. Further, from the UV–Vis spectra, it is found that bandgap contracts due to the formation of defects. The DC emission spectra (λex = 325 nm) show an enhancement of polychromatic emission as a function of the Sm concentration and tune from orange to red along with the transition from the warm to cool region in the Commission International de l'Eclairage 1931 XY spectral chromaticity coordinates. X-ray absorption spectra confirm the presence of Fe2+/Fe3+ ions and Sm3+ ions. Using the decay kinetics and transfer efficiencies, the energy transfer between the host defect levels and dopant ions is explained with the help of the energy level diagram. The UC emission spectra (λex = 980 nm) exhibit monochromatic red emission along with a strong near-infrared emission lying in the cool region with 100% color purity. These phosphors are expected to find applications in solid-state lighting applications, optoelectronics, and biomedical engineering, etc.