Li+-doped cubic Gd1.88Eu0.12O3 powders were synthesized at 1200 °C by the solid state reaction method. Under excitation of the charge transfer band of Eu3+ at 245 nm, the Gd1.88Eu0.12O3 exhibited a dominant photoluminescence (PL) red emission peak at 611 nm, which is attributed to the electric dipole transition 5D0→7F2 of Eu3+. The dominant PL red emission peak intensity increased with Li+ doping and reached a maximum in the range from 12 to 16 mol%. This intensity was approximately 3 times higher than that of undoped Gd1.88Eu0.12O3. Chemical composition analysis revealed that the Li+ species was completely evaporated from the samples by the heat treatment up to 1200 °C. However, during the heat treatment at 600-1000 °C, the doped Li+ could promote formation of a liquid phase, which enhanced the crystallite growth of cubic Gd1.88Eu0.12O3 by Ostwald ripening. The thermal stability of the cubic Gd1.88Eu0.12O3 was also improved with respect to the amount of Li+ doping. Even after annealing at 1300 °C (higher than the cubic/monoclinic phase transformation temperature of 1250 °C) for 72 h, X-ray diffraction pattern analysis indicated that the relative fraction of the cubic phase in the 12 mol% Li+-doped sample was as high as 90%. The relationship between the amount of Li+ doping and the asymmetric ratio evaluated for the PL emission spectrum and PL quantum efficiency of the cubic Gd1.88Eu0.12O3 samples suggested that, in addition to enhanced crystallite growth, the formation of additional oxygen vacancies promoted by Li+ doping contributed to simultaneous enhancement in the PL red emission intensity and the thermal stability of cubic Gd1.88Eu0.12O3 investigated in this study.
ASJC Scopus subject areas
- 化学 (全般)