Growth and characterisation of RbTiOPO4 : Nb crystals as a host for rare earth ions

Abstract

The growth of RbTiOPO4 crystals doped with Nb (RTP:Nb) by the Top Seeded Solution Growth (TSSG) technique is studied in order to obtain a suitable host for rare earths. Preliminary crystallographic and optical characterisations of these crystals show that the birefringence of the crystal increases with Nb incorporation, while the second harmonic generation capability is practically unmodified with respect to RTP. Moreover, a small but significant increase in the cut-off wavelength of the UV band edge with Nb incorporation is also found. Single crystals of RTP:Nb:Er and RTP:Nb:Yb by TSSG have been grown and no important changes with respect to the growth of RTP:Nb have been observed. The concentrations of rare earths achieved are [Er3+]=0.65×1020 atoms·cm−3 and [Yb3+]=1.95×1020 atoms·cm−3. Polarised optical absorption spectra of Er3+ and Yb3+ in a RTP:Nb matrix are studied at 6 K and at room temperature.