CaGdAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays

Abstract

Eu³⁺ and/or Tb³⁺-doped CaGdAlO₄ phosphor samples were synthesized via a conventional high temperature solid-state reaction process. X-Ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) as well as cathodoluminescence (CL) spectra were used to characterize the samples. For CaGdAlO₄:Tb³⁺, the concentration of doped Tb³⁺ has a significant effect on the ⁵D₃/⁵D₄ emission intensity due to the dipole–dipole cross-relaxation mechanism from ⁵D₃ to ⁵D₄. Under the 4f⁸ → 4f⁷5d excitation of Tb³⁺ or low-voltage electron beam excitation, the CaGdAlO₄:Tb³⁺ samples show tunable luminescence from blue to cyan and then to green with the variation of the Tb³⁺-doping concentration. For CaGdAlO₄:Eu³⁺, the samples exhibit a reddish-orange emission corresponding to the ⁵D_0,1 → ⁷F_0,1,2,3 transitions of Eu³⁺. Energy transfer can take place from Tb³⁺ to Eu³⁺ when they are codoped in one host. Furthermore, for CaGdAlO₄:Tb³⁺/Eu³⁺, a white emission can be realized in the single phase CaGdAlO₄ host by reasonably adjusting the doping concentrations of Tb³⁺ and Eu³⁺ under low-voltage electron beam excitation. Due to the excellent PL, CL properties and good CIE chromaticity coordinates, the as-prepared Tb³⁺/Eu³⁺-doped CaGdAlO₄ nanocrystalline phosphors have potential applications in field emission display devices.