Enhanced upconversion emission in ZrO2–Al2O3 composite oxide

Abstract

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 Er³⁺-doped samples was studied. An enhancement of the green UC emission by as much as 22 times was achieved by co-doping with Yb³⁺ and Mo⁶⁺ 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 Er³⁺. 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 ⁴F_7/2 level of the Er³⁺ 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.