Enhanced upconversion emission in ZrO₂-Al₂O₃ composite oxide

Aqueous solutions of zirconium oxychloride and aluminum nitrate were coprecipitated and crystallized to form a ZrO2-Al2O3 solid solution. The upconversion (UC) emission from different Er(3+)-doped samples was studied. An enhancement of the green UC emission by as much as 22 times was achieved by co-doping with Yb(3+) and Mo(6+) ions due to an energy transfer at a higher excited-state energy, which partly avoided the non-radiative decay processes at the lower energy levels of Er(3+). The UC emission of the ZrO2-Al2O3 composite system series doped with different agents was enhanced. Excess oxygen vacancies are generated by forming ZrO2-Al2O3 solid solutions, which have an energy level close to the (4)F7/2 level of the Er(3+) ions. The defect state promoted the energy transfer process resulting in an eight-fold increased green UC emission in ZrO2-Al2O3 solid solutions. The solid solutions have a superior color chromaticity of x = 0.25 and y = 0.71 due to the evident enhancement in the green to red emission ratio in the 8ZrO2-2Al2O3 sample.