Site-selective energy upconversion in CaF2:Ho3+

From the absorption spectrum of CaF2:Ho3+, Judd-Ofelt intensity parameters were estimated as Ohm(2) = 0.018 x 10(-20) cm(2), Ohm(4) = 0.57 x 10(-20) cm(2), and Ohm(6) = 0.587 x 10(-20) cm(2). 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 CaF2:Ho3+ with efficiencies of 0.08%, 0.13% and 1.35 x 10(-3)%, respectively, on resonant excitation of the F-5(5) 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 I-5(4) State we detected strong green upconversion signals from the S-5(2) State and found that excited-state absorption from I-5(7) was responsible for this process. Upconversion efficiency of the process was determined to be 8.1%. On resonantly exciting the I-5(5) state, we detected strong red emission in CaF2:Ho3+ and strong green emission in LaF3:Ho3+. Such a host-dependent upconversion frequency emission is also explained. (C) 1997 Optical Society of America.