Excitation of uv Fluorescence in LaF3Doped with Trivalent Cerium and Praseodymium

Abstract

We have investigated the excitation of uv and visible fluorescences in La${\mathrm{F}}_3$:${\mathrm{Ce}}^{3+}$ and La${\mathrm{F}}_3$:${\mathrm{Pr}}^{3+}$ pumped through the $5d$ and $6s$ bands of the impurity ion. We have also investigated the pumping bands in absorption. Several Stark components of the $5d$ bands of ${\mathrm{Ce}}^{3+}$ and of ${\mathrm{Pr}}^{3+}$ in La${\mathrm{F}}_3$ have been identified. We report uv and visible emissions originating from the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state of the ${\mathrm{Pr}}^{3+}$ ion at 2500, 2700, and 4000 Å and a broad-band fluorescence (2700-4500 Å) in ${\mathrm{Ce}}^{3+}$ with bandwidth dependent on doping. Using the Judd-Ofelt theory we have calculated the line strengths and transition probabilities for the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ emissions, obtaining a lifetime for that state of 3.6 μsec. Measurement of the lifetime yielded a value of 720 nsec. The lifetime for the cerium emissions was found to be 20 nsec. The threshold for stimulated emission in the transitions of La${\mathrm{F}}_3$:${\mathrm{Pr}}^{3+}$ has been calculated and the possibility of uv lasing is discussed.