SrB4O7 : Sm2+: crystal chemistry, Czochralski growth and optical hole burning

The crystal chemistry of the Sm3+ to Sm2+ reduction in tetraborate lattices was investigated. In crystalline SrB4O7 in air it is mainly Sm2+ that is i ncorporated from a melt or glass containing predominantly Sm3+. For the pro cess in air, a reduction and pick-up mechanism is assumed to take place at the crystal/nutrient interface. Stabilization of Sm2+ in SrB4O7 at high tem perature and in an oxidizing atmosphere seems to be a particular property o f the system, because no Sm2+ inclusion could be observed along the series MB4O7 (M = Ca, Ba, Cd, Pb), if similar reaction conditions were applied. So far, there is only one other oxide lattice (BaB8O13) known where at high t emperatures significant amounts of Sm2+ are obtained for reactions in the a ir. Single crystals of SrB4O7 : Sm2+ were grown by the Czochralski method (k(ef f) for Sm is 0.5). Optical hole burning experiments for the transition D-5( 1)-F-7(0) were performed at 80 K. A hole with a width of 0.21 cm(-1) and a depth of 5.25% was formed for the first time for Sm2+ in a borate crystal e xcited by the beam of a single frequency dye laser. A rather small inhomoge neous linewidth of 0.28 cm(-1) allowed the burning of a single hole only.