Synthesis and Characterization of MgCr₂O₄:Co²⁺ Fabricated by a Microwave Method

Abstract

Co²⁺-doped MgCr₂O₄ nanocrystals were prepared by a microwave method. Polyvinyl alcohol (PVA), as well as Mg and Cr nitrates, with a molar ratio of metal ion to PVA monomer unit of 1:3, was irradiated with 2.45 GHz microwaves at microwave powers ranging from 400 to 900 W. These were used as precursors for Co²⁺-doped MgCr₂O₄ spinels. The Co²⁺-doped MgCr₂O₄ nanocrystals were produced by calcining the precursors at temperatures above 500°C. They were then characterized by X-ray diffraction (XRD), the results of which suggest that MgCr₂O₄ nanocrystals with good spinel structures can be prepared via the microwave method. Infrared (IR) spectra showed that PVA was decomposed. The observed excitation and emission spectra of nanocrystalline powders in the visible regions were characteristic of tetrahedral Co²⁺ ions, indicating that Co²⁺ ions entered the MgCr₂O₄ crystal by replacing tetrahedral Mg²⁺ ions. The bands at 677.6 nm are assigned to spin-allowed ⁴T₁(⁴P) →⁴A₂(⁴F) transitions.

Keywords:

• Microwave
• MgCr₂O₄:Co²⁺
• Nanocrystal

ACKNOWLEDGMENTS

We would like to acknowledge our gratitude for the financial support provided for this work by the National Natural Science Foundation of China (20976100), the Natural Science Foundation of Shandong Province of China (ZR2009BM030) and the Special Funds for Scientific Star Project of Jinan City of China (20100122). The authors also thank Professors Guowei Zhou and Liguo Zhou for their kind help.