Comparative investigation on structure and luminescence properties of fluoride phosphors codoped with Er3+/Yb3+

This paper reports on comparative investigation of structure and luminescence properties of tetragonal LiYF4 and BaYF5, and hexagonal NaYF4 phosphors codoped with Er3+/Yb3+ by a facile hydrothermal synthesis. The products were characterized by X-ray diffractometer, scanning electron microscope, and photoluminescence spectroscopy. Intense visible emissions centered at around 525, 550 and 650 nm, originated from the transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 of Er3+, respectively, have been observed in all the samples upon excitation with a 980 nm laser diode, and the involved mechanisms have been explained. Based on the green up-conversion emission performance, the Yb3+ concentrations of Er3+/Yb3+-codoped LiYF4, BaYF5, and NaYF4 phosphors have been optimized to be 10, 20, and 20 mol.%, respectively. The quadratic dependence of fluorescence on excitation laser power has confirmed that two-photon contribute to up-conversion of the green–red emissions.