Laser-induced fluorescence and up-conversion processes inLiYF4:Nd3+laser crystals

Tunable-pulsed-laser spectroscopy was used to investigate the anti-Stokes fluorescence of the ${\mathrm{Nd}}^{3+}$ ion in ${\mathrm{LiYF}}_4$ crystals. On the basis of time-resolved measurements at 4.4 K, the observed fluorescence lines in the near uv and blue region (356–417 nm) were assigned to transitions from the ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{3/2}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{3/2}^{}{}_{}{}^{}$ excited states. These emissions were examined under both one- and two-photon laser excitations. These excitation conditions, added to the time-resolved-spectroscopy technique, provide convincing arguments for a detailed description of the various high-energy ${\mathrm{Nd}}^{3+}$ states in ${\mathrm{LiYF}}_4$. The dominant process leading to anti-Stokes fluorescence was attributed to an excited-state absorption from the ${}_{}{}^4{}_{}{}^{}\mathrm{F}_{3/2}^{}{}_{}{}^{}$(1) and ${}_{}{}^4{}_{}{}^{}\mathrm{F}_{5/2}^{}{}_{}{}^{}$ states, which were probed by a two-color laser excitation experiment. The kinetics of deexcitation of the ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{3/2}^{}{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{3/2}^{}{}_{}{}^{}$, and ${}_{}{}^4{}_{}{}^{}\mathrm{F}_{3/2}^{}{}_{}{}^{}$ states were investigated under various excitation conditions and over a wide range of temperatures. A detailed discussion emphasizes relaxation of the excited states.