Effect of Annealing on PL Intensity of NaYF4:Er3+, Yb3+/Ca2+ Phosphor and the Application to Temperature Sensor

We have prepared NaYF4:Er3+/Yb3+/Ca2+ phosphors using the solvothermal method and discussed the influence of annealing on the crystal structure, morphology, and photoluminescence characteristics in this work. The results show that, with the increase of annealing temperature, the crystallization phase changes from a single cubic structure to a mixed phase of cubic and hexagonal phases and the morphology is also condensed from spherical particles to sheets. In particular, the PL intensity of the annealed phosphor becomes much stronger than that of the unannealed phosphor. An annealed NaYF4:Yb3+, Er3+/Ca2+ phosphor is selected as an example to investigate the performance of high temperature sensor based on the fluorescence intensity ratio between two green emissions. The measurement range and the maximum absolute sensitivity S-A of the annealed sensor material are superior to the corresponding parameters of the same phosphor without annealing. The curve of relative sensitivity curve S-R decreases as the ambient temperature increases, but that of the revolution delta T presents an opposite trend. All the results show that the NaYF4:Er3+/Yb3+/Ca2+ phosphor is more suitable for application on the high temperature sensor after annealing.