Optical spectroscopy of Ho3+ and Tm3+ ions in KTiOPO4 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 2 O:33.2P 2 O 5 :16.32TiO 2 :0.68RE 2 O 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.