Enhanced Band Gap, Optical and Near-Infra-Red Reflecting Properties of Environmentally Benign Synthesized Nanocrystalline Gd₂Ti₂O7 Pyrochlore Materials.

Abstract

The recent trend of reflecting the NIR rays with cool and color pigments to reduce the transfer of heat inside the buildings is highly encouraged. In this work, the pyrochlore-type Gd₂Ti₂O7 nanomaterials were synthesized through a hybrid process comprising planetary ball milling and chloride salt flux method. Different combination of alkali metal chloride fluxes was used to enhance the phase formation and purity. In order to investigate the phase formation, purity, particle size, optical property, morphology and elemental composition of the prepared samples, many characterization techniques including XRD, RAMAN, FT-IR, UV-vis, NIR, PL, and HRSEM-EDX were carried out. The XRD patterns revealed that the annealed materials crystallized in cubic structure with lattice parameter, a = 1.019(1) nm, and the ball milled product annealed with LiCl:NaCl and LiCl:CsCl flux crystallized in a single cubic phase with high purity. The FT-IR analysis confirmed the presence of metal oxide bonds (Gd-O vibration and Ti-O-Ti bending vibration) in the wavenumber regions 400 cm-1 and 500 cm-1. The band gap of the Gd₂Ti₂O7 powder is enhanced from 2.77 eV to 3.27 eV through the addition of LiCl:CsCl flux. The PL emission property of Gd₂Ti₂O7 is enhanced by annealing with flux under the excitation wavelength of 230 nm. Further, the band gap and NIR reflectivity of the nanomaterials are enhanced by the conditions employed in the synthesis method.