Optical spectroscopy of Ho 3+ and Tm 3+ ions in KTiOPO 4 single crystals

Abstract

KTiOPO 4 single crystals doped with Ho 3+ or Tm 3+ ions have been grown by the top seeded solution growth (TSSG) slow cooling technique using a 49.8K 2O:33.2P 2O 5:16.32TiO 2:0.68RE 2O 3 (RE=Ho, Tm) flux. The holmium and thulium concentrations obtained in the crystal are [Ho]=340 ppm and [Tm]=500 ppm, and the corresponding distribution coefficients K Ho=2.7×10 −3 and K Tm=5.1×10 −3. Sharp optical absorption bands corresponding to Ho 3+ and Tm 3+ ions have been measured at 4.2 K. For both ions the optical absorption shows a dichroic character, generally being more intense when the polarization of the light is parallel to the c-axis of the crystal and weakest when the light is polarized parallel to the a-axis. Photoluminescence has been excited at room temperature in KTP:Tm crystals by using the 476 nm light of an Ar laser.