UV Excited Intense Red Emitting Gd_2-x-yEu_xO₃:yY³⁺ Nanophosphors with High Thermal Stability for pc-LED Applications

The present study deals with the synthesis and characterization of the Gd₂O₃:Eu³⁺ nanophosphors and the impact of Y³⁺ co-doping on the structural and optical properties of the Gd₂O₃:Eu³⁺. All nanophosphors are synthesised by facile low temperature solution combustion method using citric acid as a chelating agent. The XRD pattern of as-synthesised Gd₂O₃:Eu³⁺ confirmed the presence of mixed-phase crystallites and upon annealing, it transforms to a cubic phase. The images of TEM and FE-SEM confirm that the samples are spherical after annealing. From the perspective of the emission spectra of Gd₂O₃:Eu³⁺, the ⁵D₀ to ⁷F₂ (613 nm) optical transition is the most important among the different narrow emission peaks observed in the visible region. Optimal doping concentration of Eu³⁺ was 7 wt%. Y³⁺ ions were incorporated into this Gd₂O₃:7 wt%Eu³⁺ nanophosphors. Y³⁺ co-activated samples crystallized in the cubic structure and exhibited a threefold enhancement in emission intensity and considerable improvement in lifetime and quantum efficiency compared to Gd₂O₃:Eu³⁺ nanophosphors. Temperature-dependent PL spectra indicate that the obtained nanophosphor exhibits excellent thermal stability and the activation energy was observed to be 0.4773 eV. Beyond that, red CIE coordinates, with excellent colour purity (greater than 95%) and suitable colour-correlated temperature (below 5000 K) suggest that the prepared red-emitting nanophosphors have immense potential in phosphor converted LED (pc-LED) applications.