Fluorescence and Energy Transfer between Nd3+ and Yb3+ in LaF3

Energy transfer has been observed in single crystals of LaF3 codoped with Nd3+ and Yb3+ resulting from the near resonance transitions between states of Nd3+ and the 2F7/2→2F5/2 states of Yb3+. From an analysis of the fluorescence and absorption spectra of Yb3+, all the crystalline field Stark components of the 2F7/2 and 2F5/2 state were determined. The four crystal sublevels of the 2F7/2 ground states are found at 0, 185, 401, and 870 cm−1. The three levels of the excited 2F5/2 states are determined at 10 260, 10 430, and 10 660 cm−1, respectively. Based on these values of the Stark levels, the spin—orbit coupling radial integral for Yb3+ in LaF3 is calculated to be 2882 cm−1.