Spectroscopic investigations of the 4ƒ5d energy levels of Pr^3+ in fluoride crystals by excited-state absorption and two-step excitation measurements

Excited-state absorption spectra obtained by a pulsed pump–probe technique specially designed for the near-UV spectral domain were recorded in three ${\mathrm{Pr}}^{3+}$-doped fluoride crystals $({\mathrm{KY}}_3{\mathrm{F}}_{10},$ ${\mathrm{LiYF}}_4,$ and ${\mathrm{BaY}}_2{\mathrm{F}}_8).$ These excited-state absorption spectra correspond to optical transitions from the ${ }^3{P}_0$ or the ${ }^1{D}_2$ metastable levels of the $4f^2$ configuration up to the first energy levels of the $4f5d$ electronic configuration. The position, the anisotropic behavior, and the line shape of the observed excited-state absorption bands are discussed and compared with ground-state absorption (from level ${ }^3{H}_4)$ or direct excitation spectra available in the literature. Subsequently, two-step excitation into the $4f5d$ high-lying energy levels of ${\mathrm{Pr}}^3$ by means of ${ }^3{P}_0$ and ${ }^1{D}_2$ is shown to be an efficient way to produce broadband UV fluorescence by use of pump beams in the blue and the near UV.