Annealing temperature enhanced visible absorption and magnetic properties of (Cu, Cr) co-doped ZnO diluted magnetic semiconductors

Abstract

Cu and Cr co-doped ZnO nanopowder (Zn0.96Cu0.02Cr0.02O) had been synthesized by co-precipitation method and the nanopowders were annealed at 400 ˚C (S1), 600 ˚C (S2), and 800 ˚C (S3). The sample S2 had better crystallization with a lesser amount of defects and imperfections. However, the presence of impurities and imperfection in sample S1 and lattice distortion due to the thermal expansion of lattice in sample S3 were noticed in the XRD pattern. All the samples had wide absorption and emission bands in the UV/violet, blue and green regions due to the d-d transition of metal ions. The Cr3+ ions in the tetrahedral environment undergo crystal field splitting. The violet band centered at 435 nm, blue emission centered at 478 nm, and green emission centered at 520 nm are ascribed due to the transition from 4T1(4P) to 4A2(4F), 4T1(4F) to 4A2(4F), and 4T2(F) to 4A2(4F) respectively. The visible absorption and emission of the nanopowders had been enhanced by annealing. All the samples had room-temperature ferromagnetism (RTFM) and the sample S2 had maximum saturation magnetization among others.