Spectroscopy and excitation dynamics of the trivalent lanthanides thulium(3+) and holmium(3+) in yttrium lithium fluoride

A detailed study of the spectroscopy and excitation dynamics of the trivalent lanthanides Tm{dollar}sp{lcub}3+{rcub}{dollar} and Ho{dollar}sp{lcub}3+{rcub}{dollar} in Yttrium Lithium Fluoride, LiYF{dollar}sb4{dollar} (YLF), has been done. YLF is a very versatile laser host that has been used to produce laser action at many different wavelengths when doped with trivalent lanthanides. Since the early 1970's YLF has been the subject of many studies, the main goal of which has been to produce long wavelength lasers in the eye safe 2{dollar}mu{dollar}m region. This study concentrates on a presentation and analysis of the spectroscopic features, and the temporal evolution of excitation energy in YLF crystals doped with Tm{dollar}sp{lcub}3+{rcub}{dollar} and Ho{dollar}sp{lcub}3+{rcub}{dollar} ions.; Absorption spectroscopy is studied to identify wavelength regions where energy can be absorbed in Holmium YLF and Thulium YLF, and to determine their respective absorption cross sections. These measurements are applied in the Judd-Ofelt theory to determine radiative transition rates of spontaneous emission. Luminescence spectroscopy is studied under cw diode laser excitation at 785nm. The effect of dopant ion concentration and excitation power on the observed luminescence are considered in these measurements. An analysis of these measurements have been used to determine channels of energy transfer between Tm{dollar}sp{lcub}3+{rcub}{dollar} and Ho{dollar}sp{lcub}3+{rcub}{dollar} ions (cross relaxation, upconversion, and resonant energy transfer). The temporal response of Tm and Ho in singly and co-doped YLF to pulsed laser excitation with a Ti:Al{dollar}sb2{dollar}O{dollar}sb3{dollar} laser and a CoMgF{dollar}sb2{dollar} laser tuned to various wavelengths have also been studied. The energy transfer mechanisms of cross relaxation, upconversion, and resonant energy transfer between Tm{dollar}sp{lcub}3+{rcub}{dollar} and Ho{dollar}sp{lcub}3+{rcub}{dollar} ions have been modeled, and the model parameters extracted by a fitting procedure to the measured temporal response curves. Rate equation approaches to modeling are presented that result in predictions of rate constants for energy transfer processes, as well as more conventional approaches to modeling such as the Forster-Dexter models, which give the interaction strengths in terms of microscopic interaction parameters.