Laser-induced fluorescence-line-narrowing studies of impurity-ion systems: LaF3:Pr3+

Abstract

The technique of time-resolved fluorescence line narrowing has been applied to the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state in La${\mathrm{F}}_3$:${\mathrm{Pr}}^{3+}$ Investigations included not only the low-concentration limit, but also samples of higher concentration. By sampling the fluorescence signal very shortly after the excitation pulse, measurements of homogeneous widths were undertaken. It is shown that the effect of "accidental coincidence" plays an important role in the analysis of nonresonant linewidths at low temperatures. Also considered are differences in the dependence of the excited-state energies on the crystal-field strength. By properly accounting for these effects, it is shown that all of our linewidth data can still be explained by the existing theory of phonon-induced relaxation. An extensive discussion is given of time-resolved studies exhibiting the effect of phonon-assisted spectral diffusion. Included are results that have been reported previously. Finally, at higher concentrations, a variety of new effects have been observed. These include "pseudodiffusion," line-shape and linewidth variations in the nonresonant transition, and a variation of the $\frac{1}{e}$ lifetime of the excited state as a function of the absorption frequency. These effects are attributed to strongly concentration-dependent satellite lines that, at these higher concentrations, are now folded into the broadened main line. It is pointed out that when dealing with conventional line-shape and decay-curve measurements in samples of higher concentration, the possible presence of all of these effects has to be considered and properly accounted for.