Study On Preparation Of TlBr Nutrient And Seed Crystal

TlBr single crystals are promising materials as room temperature X- and gamma-ray detectors due to their high average atomic numbers (Tl: 81,Br: 35), density (7.56 g/cm3) and wide band gap (2.68 eV). TlBr crystal detectors exhibited high detection efficiency and good energy resolution for 5.9 KeV~1.33 MeV at room temperature and at -20℃. However, it is difficult to grow high purity, high quality and large-sized crystals for TlBr radiation detectors at present. In this paper, TlBr single crystal growth method from molten has been sdudied to growth large-sized, integrated TlBr single crystal by spontaneous nucleation, and then TlBr nutrient and seed crystal were prepared.Frist, light yellow transparent single crystal with dimension up toΦ8 mm×12 mm have been grown by vertical gradient decreasing temperature method. X-ray diffraction indicated that the as grown crystal is integrated single crystal. The best conditions were defined by comparison analysis of the crystal growth process. The single zone vertical furnace and quartz ampoule with 8 mm in diameter and 18-40 degrees in taper were applied to grow TlBr single crystals directly from commercially available TlBr powder (98.5%). The temperature gradient of the growth region was 0.8-1.5℃/mm. Then decrease temperature to 440℃with a rate of 5℃/h after the initial material totally melt down under the temperature of 520-550℃.The relationship between single crystal growth conditions and crystal integrality were analysed through X-ray diffraction and rocking curves for (110) planes of the wafers from the top, mid and tail of the ingot growth under different conditions. The results showed that higher quality crystal can be obtained with smaller taper and larger temperature gradient of the growth region. Two X-ray diffraction peaks of the (110) faces have been observed, which indicated that the as grown crystal is integrated single crystal. The rocking curves of X-ray diffraction were measured for (110) planes of the wafers from the top, mid and tail of the ingot TlBr(8-12). Variance of the shape for rocking curves was analyzed. At last, we characterized the crystal quality by infrared transmission spectra of the wafers from the mid and tail of the ingot TlBr(8-12). The forms of the curves are similar to each other with transmittance decreased in linear form while the wavenumber (frequency) increasing from 400 cm-1 to 4000 cm-1. The average transmittance is about 40% that lower than the theory value would due to the imperfect structure, i.g. the deformation of the lattice. The bandgap value obtained from the position of the absoption edge of an UV transmission measurement was 2.84 eV.This work will be significant not only for the study of TlBr single crystals growth by hydrothermal method but for the high-quality TlBr single crystals growth and the detector manufacturing.