Laser and infrared spectroscopy of Nd3+ and Pr3+ ions in fluorite crystals (2003)
AuthorsNelson, Julieshow all
Laser-selective excitation and infrared absorption spectroscopy have been employed to establish energy-level schemes for trivalent Nd3+ and Pr3+ centres in alkaline-earth fluoride crystals. For studies involving Nd3+, the addition of NaF and LiF co-dopants has been shown to promote cubic and C2v centres at the expense of locally compensated fluorine sites. Here dopant concentrations in the order of 0.1 mol% (Nd3+) and 1.5 mol% (NaF/LiF), were effective in removing interstitial fluorine ions. The Nd3+ cubic centre is characterised by a very narrow line-width vibronic transition, which does not correspond to a peak in the CaF2 phonon density of states. The vibronic interval has been measured as 141 cm-1 in CaF2:Nd3+ and 152 cm-1 in SrF2:Nd3+. These vibronics are believed to be associated with pseudo-localised resonance modes, which are dependent upon the lanthanide mass. A crystal-field analysis, involving both the cubic and C2v centres in CaF2:Nd3+ and SrF2:Nd3+ has been performed. The inclusion of a correlation crystal-field parameter was successful in improving the fit to all multiplets, especially the problematic 2H11/2 multiplet. Laser spectroscopy was used to characterise three oxygen centres in CaF2:Pr3+. This included the first comprehensive study of the CaF2:Pr3+ D and B sites. Energy level schemes, involving seven multiplets in Pr3+, were established for all centres.