Growth of Cu-doped Li2B4O7 single crystals by vertical Bridgman method and their characterization

Abstract Lithium tetra borate (Li 2 B 4 O 7 , LBO) single crystals with Cu as dopant have been grown by the vertical Bridgman method. A special crucible arrangement with three separate crucibles welded together was used for the crystal growth. Cu 2 O was added at different concentrations varying in the range 0.0025–0.1 wt%. The grown crystals were cut and polished for observation under optical and scanning electron microscopes. Optical micrograph showed presence of voids, which propagate along the growth direction. Scanning electron microscope coupled with energy dispersive X-ray analyzer showed segregation of Cu in these voids, which might be due to constitutional supercooling. Optical transmittance measured across 5 mm thick samples indicated that the absorption around 240 nm increased with the increase in Cu concentration. Excitation–emission measurement was carried out to estimate peak emission and excitation wavelengths. The dependence of Cu concentration in LBO on the emission intensity has also been evaluated.