Controlled Synthesis of Tb³⁺/Eu³⁺ Co-Doped Gd₂O₃ Phosphors with Enhanced Red Emission

(Gd_0.93-Tb_0.07Eu)₂O₃ (x = 0⁻0.10) phosphors shows great potential for applications in the lighting and display areas. (Gd_0.93-Tb_0.07Eu)₂O₃ phosphors with controlled morphology were prepared by a hydrothermal method, followed by calcination at 1100 °C. XRD, FE-SEM, PL/PLE, luminescent decay analysis and thermal stability have been performed to investigate the Eu³⁺ content and the effects of hydrothermal conditions on the phase variation, microstructure, luminescent properties and energy transfer. Optimum excitation wavelength at ~308 nm nanometer ascribed to the 4f⁸-4f⁷5d¹ transition of Tb³⁺, the (Gd_0.93-Tb_0.07Eu)₂O₃ phosphors display both Tb³⁺and Eu³⁺ emission with the strongest emission band at ~611 nm. For increasing Eu³⁺ content, the Eu³⁺ emission intensity increased as well while the Tb³⁺ emission intensity decreased owing to Tb³⁺→Eu³⁺ energy transfer. The energy transfer efficiencies were calculated and the energy transfer mechanism was discussed in detail. The lifetime for both the Eu³⁺ and Tb³⁺ emission decreases with the Eu³⁺ addition, the former is due to the formation of resonant energy transfer net, and the latter is because of contribution by Tb³⁺→Eu³⁺ energy transfer. The phosphor morphology can be controlled by adjusting the hydrothermal condition (reaction pH), and the morphological influence to the luminescent properties (PL/PLE, decay lifetime, etc.) has been studied in detail.