In this letter, we demonstrate for the first time a growth of monoclinic phase ZrO2 nanocrytals based on a sol-gel method, compared to the ordinary sol-gel procedure, our method decreases the synthesized temperature from ∼1000 °C to ∼800 °C. In addition, it is found that Er3+ in monoclinic phase ZrO2 nanocrystals have greatly enhanced upconversion emissions under infrared LD excitation due to its lower environmental symmetry.
