Optical properties and laser induced fluorescence from BGO:RE waveguides

The formation of optical waveguides in bismuth germanate doped rare earth elements (Bi_3Ge_4O_1_2:RE) has been studied. The samples were implanted with 77 K. The energy and the dose of the He implanted samples are 2 Mev and 5x10"1"6 ions/cm"2 respectively. The samples were annealed for one hour from 250 to 450 deg. C. The losses of the waveguides have been measured and found to be improved with increasing annealing temperature. The ion beam modified the surface of the bulk material so within the region of the waveguide there is an optical rotation, which was observed after 450 deg. C temperature annealing. A net optical rotary power was found to be around 4.1, and 57.5 degree/mm for 632.8, and 488 nm wavelengths respectively. The evidence suggests this is due to a phase change of the BGO, which has been modified from the cubic structure into an anisotropic guide layer. The modified structure in the waveguide has been investigated by monitoring the SHG signal from the waveguide and comparing it with the bulk. The SHG intensity improved with increasing annealing temperature, due to removal of defects caused by the implantation. The restructuring of the implanted guide results in a modified crystal lattice and a greatly improved SHG. The effect increases with the difference between the radius of the RE ions and the Bi ion. The latter effect could be explained by the mismatch of ion size of the RE ion, which distorts the cubic structure of BGO in the implanted region to become slightly anisotropic, which in turn improves the SHG of the BGO:RE waveguide layer. The photoluminescence of the BGO:RE has been studied after excitation with an argon laser. The study was performed at room temperature as well as at low temperature for the waveguide and the bulk regions. The defects caused by the implantation broaden the luminescence spectra of the RE ions within the waveguides. Increasing the annealing temperature narrows the lines, presumably by defect removal. The spectra resemble those of the bulk after anneals at 450 deg. C. There is a correlation between the broadening and the size of the RE ion dopants. The differences between bulk and waveguide luminescence are most clearly observed for the Nd and Er ions. Reasons for this are discussed. (author)Available from British Library Document Supply Centre-DSC:DXN028946 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo