From the absorption spectrum of , Judd–Ofelt intensity parameters were estimated as cm2, cm2, and cm2. Radiative transition probabilities and radiative lifetimes were also estimated for some of the levels. We observed red-to-green, -blue, and -violet energy upconversion in with efficiencies of 0.08%, 0.13% and , respectively, on resonant excitation of the 5F5 state. Under site-selective excitation we also found that the blue-upconversion signal intensity was approximately three times larger than that of the green-upconversion signal intensity. On resonantly exciting the 5I4 state we detected strong green upconversion signals from the 5S2 state and found that excited-state absorption from 5I7 was responsible for this process. Upconversion efficiency of the process was determined to be 8.1%. On resonantly exciting the 5I5 state, we detected strong red emission in and strong green emission in . Such a host-dependent upconversion frequency emission is also explained.
© 1997 Optical Society of America