Excitation of the thulium (1)G(4) level in various crystal hosts

The transition from the thulium: (1)G(4) level into the ground state is a c andidate for the construction of a IR pumped blue upconversion laser. We re port on the excitation of the Tm:1G4 level in the Yb:Tm doped crystals GdAl O3, 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 do pant concentrations. Furthermore, energy transfer from thulium to terbium i s discussed. The results are evaluated in view of the construction of an ef ficient blue thulium upconversion laser. From the investigated crystals, Y3 Sc2Ga3O12 proves to be the most suitable host. Comparison of the measured d ata with values from the literature suggests that Y3Sc2Ga3O12 is an even mo re promising crystal than the low phonon host LiYF4. It is shown that the o ptimum thulium concentration is of the order of 0.1 at% for a ytterbium con centration of 10 at%. (C) 1999 Published by Elsevier Science B.V. All right s reserved.