Fluorescence linewidths and energy transfer in La${\mathrm{F}}_3$(${\mathrm{Pr}}^{3+}$, ${\mathrm{Nd}}^{3+}$)

Fluorescence line narrowing is used to study nonresonant linewidths in the doubly doped La${\mathrm{F}}_3$(${\mathrm{Pr}}^{3+}$, ${\mathrm{Nd}}^{3+}$) system. The linewidths from the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ to the bottom of the ${}_{}{}^3{}_{}{}^{}H_6^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}H_5^{}{}_{}{}^{}$, and ${}_{}{}^3{}_{}{}^{}F_2^{}{}_{}{}^{}$ Stark manifolds are found to increase with ${\mathrm{Nd}}^{3+}$ concentration. This increase is attributed to a residual strain broadening of the narrowed nonresonant transitions and not to a lifetime broadening of the terminal states, as originally assumed. The change in the temporal decay of the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state with ${\mathrm{Nd}}^{3+}$ concentration is used to discuss the Pr-Nd interaction.