The role of reaction conditions in the polymorphic control of Eu3+ doped YInO3: structure and size sensitive luminescence

Abstract

With the aim of exploring the effect of particle size and different polymorphic structures on the luminescence behaviour of Eu³⁺ ions, all in a single compound, the YInO₃:Eu³⁺ system was synthesized. Metastable C-type modification could be obtained in YInO₃ nanopowders synthesized by gel combustion. The broadening in Raman modes has been related to both the particle size and the strain in the metastable C-type modification. The hexagonal polymorph of YInO₃, with a layered structure, quite unlike the C-type modification, could be obtained by heating nanopowders to 1175 °C. Such a change in the structure, leading to different site symmetries for Eu³⁺ ions exhibited a tremendous bearing on its luminescence behaviour. Detailed steady state and time resolved luminescence studies revealed a highly distorted local site symmetry for the Y³⁺ ion in hexagonal YInO₃. The nano C-type YInO₃ exhibited greater asymmetry and a shorter lifetime as compared to the bulk C-type YInO₃, attributable to more surface defects in the case of the former. The Judd–Ofelt parameters (Ω₂ and Ω₄) were determined which established a much higher asymmetry in the hexagonal modification. Along with higher lifetime, the hexagonal polymorph also possessed superior quantum yield values. In addition to providing a significant insight into the structure–luminescence correlation in this study, we propose an efficient red phosphor with a high red color purity.