Growth of 2 Inch Eu-doped SrI₂ single crystals for scintillator applications

A vertical Bridgman (VB) crystal growth process was established using modified micro-pulling-down (μ-PD) crystal growth system with a removable chamber that was developed for the growth of deliquescent halide single crystals because conventional μ-PD method does not allow growth of large bulk single crystals. Eu:SrI₂ crystals were grown from the melt of (Sr_0.98Eu_0.02)I₂ composition using carbon crucibles. Undoped μ-PD SrI₂ crystals were used as seeds that were affixed to the bottom of the crucible. All the preparations preceding the growths and the hot zone assembling were performed in a glove box with Ar gas. Then the removable chamber was taken out of the glove box, attached to the μ-PD system, connected with a Turbo Molecular pump, and evacuated down to 10⁻⁴ Pa at ~300 °C. After the baking procedure, high purity Ar gas (6N) was injected into the chamber. The crucible was heated by a high frequency induction coil up to the melting point of Eu:SrI₂. After melting the starting materials, the crucible was displaced in downward direction for the crystal growth and then cooled down to room temperature. Thus, 2 in. and crack-free Eu:SrI₂ bulk crystals were produced. The crystals had high transparency and did not contain any visible inclusions. The crystals were cut and polished in the glove box and then sealed in an aluminum container with an optical window for characterization. The details of the crystal growth are discussed.