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Growth of CdWO4 Scintillation Crystals by Vertical Bridgman Process

Author: XiaoHuaPing
Tutor: ChenHongBing
School: Ningbo University
Course: Inorganic Chemistry
Keywords: Scintillation crystal CdWO4 Crystal Growth Bridgman
CLC: O782
Type: Master's thesis
Year: 2008
Downloads: 109
Quote: 1
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Abstract


Cadmium tungstate (chemical formula CdWO 4 , referred CWO) single crystal is excellent overall performance scintillation material, the crystal has a high luminous efficiency, radiation length is short, light stability, material density, no deliquescence and other characteristics, can be widely used in high-resolution-ray detection technology, especially nuclear medicine imaging, security checks and other technical fields. So far abroad have grown by Czochralski method CWO single crystal studies have reported that high-quality single crystal growth of large-size CWO there are considerable difficulties. So far not been used at home and abroad Bridgman crystal growth CWO research reports for the current CWO Czochralski single crystal growth of the technical problems, the paper work for the first time launched a CWO Bridgman single crystal growth technology research The results show that the process of bulk single crystal growth in CWO has important application value. High purity CdO, WO3 as starting materials, the application of high temperature solid state reaction CdWO 4 polycrystalline material; crucible confined conditions using the vertical Bridgman crystal growth for CWO, the furnace temperature was 1350 ~ 1400 ℃, the temperature gradient of the solid-liquid interface of 30 ~ 40 ℃ / cm, Bridgman rate of 0.5 ~ 1.5 mm / h, successfully grown sizes up? 40 × 70 mm as a pale yellow transparent CWO crystal. Application of differential thermal / thermogravimetric analysis, X-ray diffraction, transmission spectrum, the light emission spectroscopy, X-ray excited emission spectra of other methods for the characterization of the performance of the single crystal, X-ray diffraction rocking curve confirmed that the crystal lattice has good integrity resistance, transmittance spectra show that the crystal in the visible region has good optical transmission of the X-ray excitation of the crystal shows a peak wavelength of 470 nm of the strong emission of light. In order to obtain improved crystal quality and effective method of maintaining explore constant melt composition, to explore the crystal growth parameters, the growth ratio of raw materials and annealing conditions to study the occurrence of several types of crystal defects in the crystal, tested grown under different conditions CWO single crystal optical transmittance spectra and photoluminescence, and discusses different growth process on the uniformity of crystal optics. Studies show: exact stoichiometric polycrystalline material suitable for high-quality crystal growth CWO; the crucible for crystal growth under confined conditions, the melt composition can effectively avoid the volatilization CWO favor growth of high quality single crystal; using orientation [001] orientation of the seed crystal to guide the growth of the single crystal can significantly reduce the occurrence of cracking CWO; improved process can reduce the crystal generating light scattering points; in an oxygen atmosphere after the annealing process, the single crystal can reduce the oxygen CWO vacancy, improve the optical transmittance of the single crystal CWO, CWO crystal and reduce the thermal stress.

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CLC: > Mathematical sciences and chemical > Crystallography > Crystal growth > Crystal growth process
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