Trivalent cerium doped crystals as tunable laser systems: Two bad apples

The 5d-4f transitions of trivalent doped crystals have broad emission bands with large oscillator strengths and near unity quantum efficiency. These characteristics make cerium systems strong candidates for tunable solid state lasers. However, two such cerium crystals will probably never lase. The first is Ce(3+):YAG where a strong excited state absorption quenches the lasing transition. Recent measurements have indicated that the excited state absorption terminates in the YAG conduction band with a peak cross section of 1.0 x 10(-17) cm(2) at 700 nm. Some of the general features of impurity ion to band spectra are discussed. The second system is Ce(3+):CaF2 where a UV pump induced photochromic center is produced following excitation of the cerium ions. The initial measurements of cerium related transient absorptions in Ce(3+):YLF are also presented.