Size-dependent optical and thermochromic properties of Sm3Fe5O12

Abstract

Reversible thermochromic inorganic materials of Sm₃Fe₅O₁₂ with different particle sizes have been synthesized by a conventional high temperature solid state reaction method (2.51 μm) and sol–gel method (0.16 μm). The as-prepared samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), Raman, X-ray photoelectron spectroscopy (XPS) and UV-vis-NIR spectroscopy. The sizes of Sm₃Fe₅O₁₂ particles have a significant difference effect on the color of pigments. The absorption peak shifts to lower wavelength with the increase of particle size. The bandgap and lattice parameter increase with the decrease in particle size. Thermochromism for Sm₃Fe₅O₁₂ synthesized by the solid state reaction method showed a change in color from dark green to reddish brown and the samples synthesized by a sol–gel method changed from bright yellowish green to yellow. The cause of the thermochromism is the continuous red shift of ligand–metal charge transfer with the increase of temperature. This work suggests that the properties of thermochromic materials could be tuneable by particle size.