Defect states in graphene oxide mixed nanostructured calcium cobalt oxide

Abstract

Nanostructured materials of calcium cobalt oxide (Ca3Co4O9, CCO) is realized by mix-grinding the as-synthesized CCO with graphene oxide (GO) and investigated its influence on microstructure, crystallographic phase, thermal/chemical stability, molecular bonding, composition, and optical behaviour. Increasing GO weight percentage (wt%) from 0.1 to 10 in the CCO and GO mixture (CCO-GO) shows decrease in particle size with uniformly distributed sub-50 nm CCO particles and weight loss of ∼18.88% for 10 wt% GO. Structural and spectroscopic analysis of the resulting CCO-GO nanocomposites reveal coexistence of highly pure CCO and GO without comprising their inherent properties after mix-grinding. The tri-exponential behavior with weighted average lifetime of 1.21 ns in time resolved photoluminescence spectra suggest three different fundamental carrier recombination dynamics resulting from electronic transitions and photon emissions following various radiative and non-radiative processes in UV and visible range, and is attributed to the presence of defect states in CCO-GO nanostructures. The currently developed novel approach of achieving nanostructured CCO by mixing GO using an elementary and economical method of ball-milling, and conceptual understanding for presence of oxygen vacancy involved defect levels could be beneficial in developing new materials for utilization in highly efficient device applications.