Excitation of the thulium 1G4 level in various crystal hosts

The transition from the thulium: (1)G(4) level into the ground state is a candidate for the construction of a IR pumped blue upconversion laser. We report on the excitation of the Tm:1G4 level in the Yb:Tm doped crystals GdAlO3, LiGd(MoO4)(2), Y3Sc2Ga3O12 and Gd3Ga5O12. The fluorescence spectra are measured in a range from 300 to 2300 nm. The lifetimes of the Tm : (1)G(4), Tm : H-3(4) and Yb : F-2(5/2) levels are determined asa function of the dopant concentrations. Furthermore, energy transfer from thulium to terbium is discussed. The results are evaluated in view of the construction of an efficient blue thulium upconversion laser. From the investigated crystals, Y3Sc2Ga3O12 proves to be the most suitable host. Comparison of the measured data with values from the literature suggests that Y3Sc2Ga3O12 is an even more promising crystal than the low phonon host LiYF4. It is shown that the optimum thulium concentration is of the order of 0.1 at% for a ytterbium concentration of 10 at%. (C) 1999 Published by Elsevier Science B.V. All rights reserved.