Photoluminescence and cathodoluminescence properties of Li⁺ doped Gd_1.88Eu_0.12O₃

Li⁺-doped cubic Gd_1.88Eu_0.12O₃ phosphors were synthesized at 1200°C in air by co-precipitation (CP) and solid state reaction (SS) methods. X-ray diffraction analysis revealed that, regardless of synthetic method, the average crystallite size for Li⁺-free Gd_1.88Eu_0.12O₃ was approximately 400 nm, then increased with the amount of Li⁺ and at 20 mol%, reached about 2.3μm. Under excitation of the charge transfer band of Eu3+ at 245 nm, Gd_1.88Eu_0.12O₃ exhibited a dominant photoluminescence (PL) red emission peak at 611 nm assigned to the electric dipole transition 5D0=7F2 of Eu3+. The red emission peak intensity increased consistently with the amount of Li⁺-doping, while CP method was found to be effective in improving the red emission intensity at lower amounts of Li⁺-doping from 0 to 8 mol%. Cathodoluminescence (CL) property was studied by mounting the synthesized phosphor on a vacuum fluorescent display (VFD) operated at an anode voltage of 50V. The Gd_1.88Eu_0.12O₃ exhibited a similar spectrum with an intense red emission peak at 611 nm, and the highest luminance intensity for the CL red emission was achieved for 8 mol% Li⁺-doped Gd_1.88Eu_0.12O₃ synthesized by SS method. The evaluation results of PL and CL properties suggested that, besides the crystallite size of Gd_1.88Eu_0.12O₃, dispersion property of Eu3+ ions in the host Gd2O₃ was an important factor for improving luminescent properties of Gd_1.88Eu_0.12O₃. Moreover, under the present VFD operating condition at the low excitation voltage, it was thought to be essential for improving CL emission intensity to maintain a sufficient surface area of Gd_1.88Eu_0.12O₃.