Tb 3+-Yb 3+ cooperative down and up conversion processes in Tb0.81Ca0.19F2.81:Yb 3+ single crystals

The following article appeared in Journal of Applied Physics 110.12 (2011): 123527 and may be found at http://scitation.aip.org/content/aip/journal/jap/110/12/10.1063/1.3671406The energy transfer processes between Tb3 and Yb3 ions are studied in Tb-based fluoride single crystals. These are very transparent from the UV to the IR wavelength regions, except for the characteristic absorption lines of the rare-earth ions under study. In contrast with previously reported Tb 3-doped glasses and oxide powders, these crystals containing a high Tb3 concentration present two major advantages for the study of the energy transfer processes in the Tb3-Yb3 ion pair. Firstly, the adverse influence of host defects is minimized with the use of high quality crystals. Secondly, the high Tb 3 concentration guarantees a much higher absorption cross-section of UV light, and consequently these crystals have real potential for practical applications. Photoluminescence spectra in the visible-IR wavelength region demonstrate the existence of efficient down and up conversion processes by crossed excitation and emission characteristics of Tb3 and Yb3 ions. In the down conversion process, Tb3( 5D 4) → 2Yb 3( 2F 5/2), two IR photons are emitted for each Tb3 ion deexcited by second-order energy transfer to two Yb3 ions. The total quantum efficiency of the down conversion process in the fluoride system is shown to increase linearly with the Yb3 concentration, reaching its maximum at the Yb3 solubility limit in the fluoride host. Further, efficient up conversion by two- and three-IR photon absorption is observed.This work has been partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (C), 22560316, 2010