Temperature dependent upconversion luminescence of Yb/Er codoped NaYF 4 nanocrystals

The upconversion luminescence of Yb/Er codoped NaYF 4 nanocrystals was investigated at different temperatures from 295 to 10 K. The temperature dependent luminescence intensity of the nanocrystals showed very different behaviors as compared to their bulk powders. The intensity of the green emissions initially increased and then decreased as the measurement temperature was decreased. The experimental data were explained in terms of enhanced relaxation processes in the doped nanocrystals, which may need to be taken into account in many potential applications such as thermal sensing and biosensors.