Cubic Lead Fluoride Crystal Growth and Property

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Cubic Lead Fluoride Crystal Growth and Property

• Qun Deng
• Shanghai Institute of Ceramics
• Chinese Academy of Sciences

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Outline

• Introduction
• Crystal Growth
• Raw Material Preparation
• Oxygen Scavenger
• Inclusions.
• Crystal Transmission Properties
• Absorption Edge
• Transversal Transmission
• Longitudinal Transmission.
• Radiation Hardness

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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
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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
  120?C for few hours.
• XRD results confirmed that the final product is
  orthorhombic PbF2 powder.

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Crystal Growth
Bridgman Technology
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Oxygen Scavenger (I)
Lead fluoride crystal ingot grown without oxygen
scavenger
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Oxygen Scavenger (II)
Lead fluoride crystal grown with oxygen scavenger
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Longitudinal Transmission
Absorption edge of PbF2 crystals can be as good
as 245 nm
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Transversal Transmission (I)
Crystal Size 3030175 mm
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Inclusions in Crystal
Needle like inclusions
Tabular shape inclusions
Irregular shape Inclusions
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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

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Absorption at 300 nm
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Absorption of Cerium doped crystal
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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

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Transversal Transmission
Crystal Size 3030186 mm
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Radiation Hardness
P. Achenbach et al., Nucl. Instr. And Meth.,
A416, 357
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Large Size Crystal Sample
Ingot Size 7575270 mm
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Summary

• An oxygen scavenger is found to grow lead
  fluoride crystal by modified bridgman method.
  Crystal ingot size can be as large as 7575270
  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.