Crystal Growth And Properties Characterization Of Tungstate And Molydate Scintillation Materials

Scintillation crystals are optical functional materials used in the field of high-energy radiation detection. A series of scintillation crystals with excellent properties have been found in the tungstate and molybdate compound families. Some tungstate scintillation crystals are valuable in medical imaging and security checking and so on, while some molydate crystals are applied as the testing materials for nuclear physics research as they exhibit desirable luminescence properties. So far a series of tungstate crystals have been reported in previous literatures, however, few investigations about calcium tungstate(CaWO4) scintillation crystals are reported. Some research institutes reported the Czochralski growth of molybdate scintillation crystals such as calcium molybdate(CaMoO4) and zinc molybdate(ZnMoO4). This thesis present the crystal growth and properties characterization of a series of tungstate and molybdate scintillation crystals including cadmium tungstate(CdMoO4), calcium molybdate(CaMoO4), zinc molybdate(ZnMoO4) and calcium tungstate crystals. The research results are summarized as follows:(1) Feed materials preparation. Using high-purity oxide powder with 1:1 stoichiometry as initial agents, tungstate feed materials were prepared by the solid-state reaction at high temperature. Characterized the synthetic raw materials by X-Ray diffraction which were synthesized at different temperatures to obtain the optimum temperature of polycrystalline material synthesis.(2) The growth of the crystals. The prepared feed materials were enclosed into sealed crucible, the temperature gradient across solid-liquid interface was adjusted at 30~50℃/cm. Installing the rational growth temperature, growth rate and growth height according to the different crystal properties, a series of tungstate and molybdate single crystals were grown by Bridgman method successfully. The diameter of CdMoO4 was ?25×143mm while CaMoO4 was ?25×140mm, CaWO4 and ZnMoO4 single crystals were grown with cracks, but some samles were made.(3) Properties characterization. The scintillation properties of the grown crystals were analyzed. The spectra measurements showed that those tungstate and molybdate scintillation crystals had a high optical transmittance, the transmittence of the CdMoO4, CaMoO4, and ZnMoO4 was 70%, 72%, 82%, and each emission peak under ultraviolet radiation was at 525 nm, 526 nm, 529 nm. The CaWO4 crystals had a transmittence over 80% and a high emission with central wavelength at 475 nm under ultraviolet radiation and X-ray excitation.(4)stainingandannealingstudy.analysisingthecolouringmechanismofcdmoo4andcamoo4singlecrystalsandannealingthosesinglecrystalwafersinoxygenatmosphereattemperature1000℃and1100℃,becauseofthedecreaseofvacancyinthecrystalsduringannealingprocess,theopticaltransmittancecouldbeincreasedobviously.afterannealing,cdmoo4singlecrystallighttransmittancewaspromotedto75%,andandcamoo4singlecrystallighttransmittancewasover80%.