| Rare-earth doped {dollar}rm BaYsb2Fsb8{dollar} crystals are promising candidates for compact lasers particularly in the green and blue region. Upconversion pumping is often employed. However, there are only a few demonstrations of room temperature lasing emission observed in these materials.; BaY{dollar}sb{lcub}2-x{rcub}{dollar}Yb{dollar}sb{lcub}x{rcub}{dollar}F{dollar}sb8{dollar} crystals doped with {dollar}rm Er sp{lcub}3+{rcub}, Tmsp{lcub}3+{rcub}{dollar}, and Lu{dollar}sp{lcub}3+{rcub}{dollar} were grown under an HF atmosphere by the gradient-freeze method. The (010) direction was located and crystals were grown along this axis. A {dollar}rm BaYsb{lcub}1.50{rcub}Ybsb{lcub}0.49{rcub}Ersb{lcub}0.01{rcub}Fsb8{dollar} crystal pumped at 960 nm produced a 670-nm laser at 298 K. The thresholds were 32 mW for propagation perpendicular to and 45 mW for propagation along (010) (power densities of 3 and 5 {dollar}rm kWcdot cmsp{lcub}-2{rcub}{dollar} respectively). Tm{dollar}sp{lcub}3+{rcub}{dollar}- and Yb{dollar}sp{lcub}3+{rcub}{dollar}-doped crystals produced 649-, 512-, 482-, 456-, and 348-nm lasers at 298 K only when the propagation was perpendicular to (010). The 649-, 512-, 482-, and 456-nm lasers had thresholds of 45, 150, 20, and 150 mW (power densities of 5, 15, 2, and 15 {dollar}rm kWcdot cmsp{lcub}-2{rcub}{dollar} respectively). X-ray linewidth measurements indicated that line defects do not prevent crystals grown by other techniques from working as lasers. Stark level energies and polarization-averaged Judd-Ofelt parameters were determined for {dollar}rm BaYsb{lcub}1.75{rcub}Ybsb{lcub}0.20{rcub}Tmsb{lcub}0.05{rcub}Fsb8{dollar}. A total of 62 out of a possible 81 levels were found for all the states from {dollar}sp3Hsb6{dollar} to {dollar}sp1Isb6.{dollar} All the Tm{dollar}sp{lcub}3+{rcub}{dollar} lasers were assigned using these levels. The Judd-Ofelt parameters {dollar}Omegasb2, Omegasb4{dollar} and {dollar}Omegasb6{dollar} had values of {dollar}1.9 times 10sp{lcub}-20{rcub}, 0.76 times 10sp{lcub}-20{rcub}{dollar}, and {dollar}1.3 times 10sp{lcub}-20{rcub}{dollar} cm{dollar}sp2{dollar} respectively. Orientation dependent fluorescence was measured from a {dollar}rm BaYsb{lcub}1.00{rcub}Ybsb{lcub}0.99{rcub}Tmsb{lcub}0.01{rcub}Fsb8{dollar} crystal and the transition anisotropies were described by ellipsoids that were closely aligned to the optical indicatrix. The spectral anisotropies suggest best method for fabricating a laser crystal is to cut perpendicular to a growth axis that is parallel to x. |
