The microscopic interaction parameter for Tm-to-Ho resonant energy transfer in LiYF4

Absorption and luminescence measurements on Tm3+ and Ho3+ ions in LiYF4:Tm3+, LiYF4:Ho3+, and LiYF4:Tm3+, Ho3+ crystals were carried out. The data collected were used to determine the Ho3+ absorption coefficient integral for 5I8→{5I7} transition, and the integral for the overlap between the normalized Tm3+ luminescence spectrum due to the 3F4 → 3H6 transition and the Ho3+ absorption band due to 5I8→5I7 transition. The relevant critical transfer distance (R0) that gives a measure of the Tm3+-Ho3+ coupling was determined by considering a Foerster-type interaction between the ions. It was found to be 22.5 A at 300 K with the overlap integral 6.8x10-19 cm5, which is 4.41 times higher at 77 K. (author)