Growth and scintillation properties of Pr doped Gd₃(Ga,Al)₅O₁₂ single crystals

Abstract

Pr:Gd₃(Ga,Al)₅O₁₂ single crystals were grown by the micro-pulling down (μ-PD) method. All grown crystals were greenish and transparent with 3.0 mm in diameter, 15–30 mm in length. Neither visible inclusions nor cracks were observed. Luminescence and scintillation properties were measured. The substitution at the Al³⁺ sites by Ga³⁺ in garnet structure has been studied. In these crystals, Pr³⁺ 5d–4f emission is observed with 340 nm wavelength. Pr1%:Gd₃Ga₃Al₂O₁₂ shows highest emission intensity. The light yield of Pr:Gd₃Ga₃Al₂O₁₂ sample with 3 mmφ×1 mm size was around 4500 photon/MeV. Scintillation decay time was 7.9 ns (0.5%), 46 ns (0.7%) and 214 ns (98.8%).

Introduction

Scintillator materials combined with photodetectors are used to detect high energy photons and accelerated particles in medical imaging techniques, high energy and nuclear physics detectors, high-tech industrial applications and most recently also in the advanced homeland security related techniques.[1] In past decades, scintillators with the best figure-of-merit given by a combination of stopping power, speed and light yield are the recently developed Ce-activated materials [2], [3], [4], [5]. On the other hand, Pr³⁺ ion also shows the 5d–4f emission with the fast decay time in several host materials and such systems can be another candidate for high figure-of-merit scintillator. Recently our group intensively examined scintillation properties of various Pr-doped compounds [6], [7], [8], [9], [10], [11], [12], [13]. Among those materials, Pr:Lu₃Al₅O₁₂ (Pr:LuAG) was found with good scintillation properties due to high density (6.7 g/cm³), high light yield (approximately 20,000 photon/MeV), good energy resolution and a very fast 5d–4f emission decay time (20 ns)

The Gd₃Al₅O₁₂ could be also an attractive host for Ce-doped scintillators because of its relatively high density of 6.2 g/cm³ and absence of intrinsic radioactivity coming from ¹⁷⁶Lu isotope with half-life of 3.78×10¹⁰ years (2.59% natural abundance). However, Gd₃Al₅O₁₂ single crystal cannot be grown by the melt growth due to incongruent melting and phase instability [14]. Recently, some groups reported about transparent optical ceramic growth of Ce: (Gd,Y)₃Al₅O₁₂ and scintillation response of about ∼90 ns at emission around 550 nm, prospective light yield of about 11–16,000 photon/MeV and density of 6.0 g/cm³ [15], [16]. Higher density garnets such as Lu₃Ga₅O₁₂ (7.4 g/cm³), and Gd₃Ga₅O₁₂ (7.4 g/cm³) are famous crystal hosts for solid state lasers or substrate materials for epitaxial growth. However Ce³⁺ 5d–4f luminescence is quenched in these garnets because of the positioning of 5d states of Ce³⁺ in the host conduction band, which is a well-known problem in other hosts as well [17].

In this report, the Pr:Gd₃(Ga,Al)₅O₁₂ (Pr:GGAG) single crystals were grown by the micro-pulling down (μ-PD) method. Luminescence and scintillation properties were measured. The substitution phenomenon in the Al³⁺ sites with Ga³⁺ in garnet structure has been studied.