Light-induced and holographic properties of Fe, Mn and Fe+Mn doubly doped Bi₄Ge₃O₁₂ crystals

Fe, Mn and Fe+Mn doubly doped Bi₄Ge₃O₁₂ single crystals are grown by the Czochralski technique with automatically diameter-weight control. The influence of iron and manganese addition and their combination on the light-induced properties and holographic behavior at different wavelengths are investigated. All samples exhibited strong photochromic effect at room temperature, which is fully reversible after thermal annealing. Furthermore, preliminary treatments as annealing or UV exposure have been used to modify the defect structure in a crystal lattice and the corresponding absorption bands. Holographic gratings at 514 nm, 633 nm and 647 nm are successfully recorded. The diffraction efficiency and writing kinetics of the recorded holograms depend on the concrete dopant and previous illumination with UV light. Fe+Mn co-doping effect in BGO crystal leads to higher diffraction efficiency and faster response time.