Controlling the morphology and size of (Gd0.98−xTb0.02Eux)2O3 phosphors presenting tunable emission: formation process and luminescent properties

The (Gd0.98−xTb0.02Eux)2O3 phosphors have been successfully obtained using the urea-based homogeneous precipitation method in the present work. The particle growth of the precursors with mono-dispersion spherical morphology is surface-diffusion controlled and precipitated in the order of the Tb(OH)CO3 > Gd(OH)CO3 > Eu(OH)CO3, and the formation process has been also studied in detail. Partially replacing the pure water with ethylene glycol (EG) can control the particle size and morphology owing to its lower permittivity constant and interface energy. By monitoring the excitation at 314 nm (4f8 → 4f75d1 transition of Tb3+), the (Gd0.98−xTb0.02Eux)2O3 phosphors exhibit both Tb3+ (green) and Eu3+ (red) emissions at 547 and 613 nm, respectively. The presence of Gd3+ and Tb3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission directly provides an evidence of the Tb3+ → Eu3+ and Gd3+ → Eu3+ energy transfer, respectively. The quenching concentration is determined to be 2.0 at.%, and the quenching mechanism is determined to be the exchange reaction between Eu3+. The emission color can be readily tuned from approximately green to red via adjusting the Eu3+ content. The temperature-dependent analysis has been performed, and the results indicate that the (Gd0.98−xTb0.02Eux)2O3 samples possess good thermal stability. Owing to the Tb3+ → Eu3+ energy transfer, the lifetime for the Tb3+ emission rapidly decreases, and the energy transfer efficiency has been calculated. The EG addition does not bring appreciable changes to the lifetime values for the both Tb3+ and Eu3+ emissions, but enhances remarkably the luminescent intensity which confirms the variation of the particle morphology/size, and the reason can be explained by the scattering of the light. The (Gd0.98−xTb0.02Eux)2O3 phosphors developed in this work hopefully meet the requirements of various lighting and optical display applications.