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Cubic Lead Fluoride Crystal Growth and Property. Qun Deng Shanghai Institute of Ceramics Chinese Academy of Sciences. Outline. Introduction Crystal Growth: Raw Material Preparation; Oxygen Scavenger; Inclusions. Crystal Transmission Properties: Absorption Edge;
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Cubic Lead Fluoride Crystal Growth and Property Qun Deng Shanghai Institute of Ceramics Chinese Academy of Sciences
Outline • Introduction • Crystal Growth: • Raw Material Preparation; • Oxygen Scavenger; • Inclusions. • Crystal Transmission Properties: • Absorption Edge; • Transversal Transmission; • Longitudinal Transmission. • Radiation Hardness
Introduction • Density: 7.77 g/cm3 • Refractive Index: 1.82 at 400nm • Radiation Length: 0.93 cm • Moliere Radius: 2.22 cm • Energy Resolution: 3.2% at 1 GeV * • Growth difficulty: very easy to be oxidation during crystal gorwth *F.E. Mass et al., Calor2000
Raw Material Preparation • PbF2 raw material was synthesized by combining PbCO3 and HF at high temperature. • PbCO3 + HF PbF2 + CO2 + H2O • Products were put in vacuum oven and baked at 120C for few hours. • XRD results confirmed that the final product is orthorhombic PbF2powder.
Crystal Growth PbF2 Bridgman Technology
Oxygen Scavenger (I) Lead fluoride crystal ingot grown without oxygen scavenger
Oxygen Scavenger (II) Lead fluoride crystal grown with oxygen scavenger
Longitudinal Transmission Absorption edge of PbF2 crystals can be as good as 245 nm
Transversal Transmission (I) Crystal Size: 30×30×175 mm
Inclusions in Crystal Needle like inclusions Tabular shape inclusions Irregular shape Inclusions
Inclusions in Crystal(cont.) • The composition of needle-like inclusions are lead oxide or lead fluoro-oxide. • The composition of tabular and irregular shape inclusions are orthorhombic lead fluoride. • Inclusions can be eliminated by: • doping certain amount of oxygen scavenger • increasing the temperature gradient • reducing the crucible downward rate
Absorption at 300 nm (cont.) • Ce ions in raw materials may responsible for 300 nm absorption in lead fluoride crystals. • Absorption at 300nm can be attributed to 5d 4f transition of Ce ions
Transversal Transmission Crystal Size: 30×30×186 mm
Radiation Hardness P. Achenbach et al., Nucl. Instr. And Meth., A416, 357
Large Size Crystal Sample Ingot Size: 75×75×270 mm
Summary • An oxygen scavenger is found to grow lead fluoride crystal by modified bridgman method. Crystal ingot size can be as large as 75×75×270 mm. • Inclusions and scattering centers are successfully eliminated from the crystal. Very good homogeneity of large size crystals are achieved. • Ce ions in raw material is found to be responsible for 300 nm absorption in lead fluoride crystal. • The absorption edge of PbF2 can be as good as 245 nm. • PbF2 crystal still keeps good transmission after 10 krad irradiation.