Engineering of Eu dopant segregation in colquiriite-type fluoride single crystal scintillators

Yuui Yokota,Yuji Ohashi,Akira Yoshikawa,Akihiro Yamaji,Kei Kamada,Shunsuke Kurosawa

doi:10.1063/1.5006996

Abstract

Colquiriite-type Eu-doped LiCaAlF6 and LiSrAlF6 (Eu:LiCAF and Eu:LiSAF) scintillator single crystals were grown using Al metal as a starting material to improve the Eu dopant segregation. All Eu:LiCAF and Eu:LiSAF single crystals using Al metal (Eu,AlM:LiCAF and Eu,AlM:LiSAF) indicated high transparency and effective segregation coefficients (keff) of Eu2%,AlM1%:LiCAF and Eu2%,AlM1%:LiSAF single crystals were significantly improved to the value of 0.40 and 0.99, respectively. EuF3 starting material reacted with Al metal before colquiriite-type phase was generated. As a result, Eu3+ ion in EuF3 was changed to Eu2+ ion which could be incorporated into Ca2+ and Sr2+ sites easily.

Highlights

LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) single crystals with the colquiriite-type structure have been investigated as an alternative host material of neutron scintillator due to the large capture crosssection for thermal neutron originated from a 6Li isotope with the relatively large capture cross-section for thermal neutrons.[1,2,3,4,5,6]
Eu2+-doped LiCAF and LiSAF (Eu):LiCAF and Eu:LiSAF single crystals with various Eu concentrations were grown by the μ-PD method with Al metal (Eu,AlM:LiCAF and Eu,AlM:LiSAF) as shown in Figs.1(a) and (c)
Eu,AlM:LiCAF and Eu,AlM:LiSAF single crystals with various Eu concentrations were grown by the μ-PD method using Al metal as the starting material

Summary

INTRODUCTION

LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) single crystals with the colquiriite-type structure have been investigated as an alternative host material of neutron scintillator due to the large capture crosssection for thermal neutron originated from a 6Li isotope with the relatively large capture cross-section for thermal neutrons.[1,2,3,4,5,6] We have developed LiCAF and LiSAF crystals doped with various emission centers that were grown by a micro-pulling-down method which can grow single crystal from melt using a crucible with a nozzle at higher growth rate than conventional methods.[1,2,3,7,8,9] In the developed series, Eu2+-doped LiCAF and LiSAF (Eu:LiCAF, Eu:LiSAF) single crystals indicated the highest light yield under thermal neutron irradiation and they are expected to become an alternative to the 3He gas. The light yields of Eu:LiCAF and Eu:LiSAF crystals under γ-ray irradiation increased with an increase of Eu concentration and they reached to ∼ 30,000 photons/neutron at Eu 2∼3% doping level.[10,11]. In the range of more than Eu 3%, the milky parts including impurities were observed in the crystals and their amount increased with an increase of Eu concentration.[8] Generated impurities drastically decreased the transmittance of crystal which resulted in the light yield decrease with an increase of Eu concentration. The bulk crystal grown by Czochralski (Cz) method was prone to include the milky parts. The generation of milky part in the bulk crystal decreases the yield and increases the manufacturing cost of the crystals.

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION