Alkali earth co-doping effects on luminescence and scintillation properties of Ce doped Gd₃Al₂Ga₃O₁₂ scintillator

Highlights

• The Mg and Ca co-doped Ce:GAGG single crystals were prepared by μ-PD method.

• The scintillation decay curves were accelerated by Mg co-doping.

• Dominant decay time of Ce:GAGG decreased down to 39 ns by Mg co-doping.

• Mg co-doped Ce:GAGG can be promising scintillator for positron emission tomography.

Abstract

The Mg and Ca co-doped Ce:Gd₃Al₂Ga₃O₁₂ single crystals were prepared by micro pulling down method with a wide concentration range 0–1000 ppm of the codopants. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg and Ca co-doping. The scintillation decays were accelerated by both Mg and Ca codopants. Comparing to Ca co-doping, the Mg co-doped samples showed much faster decay and comparatively smaller light output decrease with increasing Mg dopant concentration.

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 the last two decades, great R&D effort brought several new material systems, namely the Ce-doped orthosilicates as Gd₂SiO₅ (GSO), Lu₂SiO₅ (LSO), (Lu_1−xY_x)₂SiO₅ (LYSO), pyrosilicates based on RE₂Si₂O₇ (RE = Lu, Y, Gd) and most recently LaX₃ (X = Cl, Br) single crystal hosts [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Oxide materials based on garnet structure single crystals are promising candidates for scintillator applications because of well mastered technology developed for laser hosts and other applications, optical transparency and easy doping by rare-earth elements. After a decade of R&D of the Lu₃Al₅O₁₂ (LuAG)-based single crystal scintillators (see review in [12]), new material concept was defined, based on multicomponent (Gd, RE)₃(Ga, Al)₅O₁₂ host, Re = Lu, Y. Doped by Ce³⁺, the Gd- and Ga rich host compositions showed amazingly high light yield up to almost 50,000 phot/MeV [13], [14], [15], [16] which is the value exceeding by 30–40% the best Ce:LYSO materials ever seen. Recently, our group reported about Ce:Gd₃Al₂Ga₃O₁₂ (GAGG) single crystal and scintillation response of about ∼90 ns at emission around 520 nm, excellent light yield of about 56,000 photon/MeV, and density of 6.63 g/cm³[15], [16]. In the silicate, perovskite and garnet scintillators the slow tunneling-driven radiative recombination between Ce emission centers and nearby lying electron traps can deteriorate scintillation performance [12], [17]. Ce:LSO and Ce:LYSO single crystals co-doped with Ca²⁺ have been recently investigated and improvement in their scintillation characteristics, namely afterglow suppression and scintillation decay acceleration, were claimed[18], [19] which is based on the suppression of such slow delayed recombination processes. Positive role of stable Ce⁴⁺ centers has been proposed in [19] to explain the improved scintillation performance. Very recently, such an approach has been used in Mg-codoped Ce:LuAG scintillation ceramics the light yield of which was enormously enhanced and the presence of Ce⁴⁺ was clearly identified by its characteristic charge transfer (CT) absorption in the near UV range below 350 nm [20]. On the contrary, strong degradation of light yield due to Ca²⁺ co-doping in Ce:GAGG has been recently reported [21].

The aim of this work is to investigate and compare the alkali earth (AE, AE²⁺ = Mg²⁺, Ca²⁺) co-doping effects on luminescence and scintillation properties of Ce:GAGG scintillator. In this report, AE co-doped Ce:GAGG single crystal were grown by the micro-pulling down (μ-PD) method and characterized as for the chemical composition. Luminescence and scintillation characteristics were also measured.