Cathodoluminescent stability of rare earth tantalate phosphors

Surface chemical changes were probed on the surface of YTaO ₄:Pr³⁺ (0.5 mol%) and LaTaO₄:Pr³⁺ (0.5 mol%) phosphors that were prepared by solid state reaction at 1200 °C, after they were exposed to a 900 C cm^-2 electron dose. X-ray diffraction confirmed the successful formation of these phosphors. The structures of YTaO₄:Pr³⁺ (0.5 mol%) and LaTaO ₄:Pr³⁺ (0.5 mol%) were found to be M′ monoclinic phases. The blue cathodoluminescence (CL) emission coming from the ³P₀→³H₄ transition of Pr ³⁺ was found to be relatively more intense than the red emission from the ¹D₂→³H₄ transition under electron beam irradiation of LaTaO₄:Pr³⁺ (0.5 mol%) and the red emission was dominant over the blue emission in YTaO₄:Pr ³⁺ (0.5 mol%). This was attributed to the position of the intervalence charge transfer state as well as a possible cross-relaxation mechanism between Pr³⁺ ion pairs in the case of YTaO ₄:Pr³⁺ (0.5 mol%). The CL and chemical changes of the surfaces of these phosphors were probed by a 2 keV electron beam at a 1×10^-6 Torr O₂ pressure using an Auger electron spectroscopy system in combination with a CL spectrometer. X-ray Photoelectron spectroscopy was used to analyze the chemical changes that took place on the surface as a result of the electron beam impingement, and it revealed the formation of new species on the surface of YTaO₄ that were called Y_xO_z, with 0<x<2, 0<z<3 and an increment contribution from Ta₂O₅ and Y₂O₃. No chemical changes were found for LaTaO₄:Pr³⁺ during electron bombardment. The stability of the CL intensity of both phosphors opens the possibility of investigating the phosphors to be used as a possible field emission display phosphor.