In-situ optical and structural insight of reversible thermochromic materials of Sm3-xBixFe5O12 (x=0, 0.1, 0.3, 0.5)

Reversible thermochromic inorganic materials of rare-earth iron garnets Sm3-xBixFe5O12 (x = 0, 0.1, 03, 0.5) with different ratio of doped Bi3+ were synthesized via high temperature solid state reaction and their structure and properties were investigated by powder x-ray diffraction (XRD), infrared spectroscopy (IR), Raman, and UV-vis-NIR spectroscopy. Refinement of the as-prepared powders XRD results indicates that the lattice constants decreased with the increasing of the doping amount of Bi3+. Thermochromism for all Sm3-xBixFe5O12 (x = 0, 0.1, 03, 0.5) samples showed the change in colour from yellow-green to brown and the substitution of Bi3+ ions also affect the colour of the samples. The initial colour of the samples is related to O2- -> Fe3+ ligand-to-metal charge transfer at 2.54 eV and d-d transitions peaking at 1.38 and 2.03 eV. The macroscopic thermochromic is originated from charge transfer at lower energy, whereas the d d is only very weakly affected. This family of materials could be applied as a thermal indicator pigments for cooking tools and hotplates. (C) 2017 Elsevier Ltd. All rights reserved.