High-perfomance Ce-doped multicomponent garnet single crystalline film scintillators

Abstract

We report for the first time the optimized content and excellent scintillation properties of single crystalline film (SCF) scintillators of multicomponent Gd3–xLux Al5–yGay O12:Ce garnet compounds grown by liquid phase epitaxy (LPE) method. The Gd1.5Lu1.5Al2.75Ga2.25O12:Ce and Gd3Al2.75–2Ga2.25–3O12:Ce SCF show the light yield (LY) comparable with that of high‐quality bulk crystal analogues of these garnets but faster scintillation decay and very low thermoluminescence in the above room temperature range. To our knowledge, these SCF possess the highest LY values ever obtained in LPE grown garnet SCF scintillators exceeding by at least 1.5–1.6 times the values previously reported for SCF scintillators. Left figure: image of Gd1.5Lu1.5Al2.75Ga2.25O12:Ce (PbO) (inset, left) and Gd3Al2.35Ga2.65O12:Ce (BaO) (inset, right) SCF scintillators, grown by LPE method onto Gd3Al2.5Ga2.5O12 (GAGG) substrate; in the middle, green–yellow light emitting by Gd1.5Lu1.5Al2.75Ga2.25O12:Ce (BaO) SCF under 350 nm laser illumination. Right figure: XRD pattern of (1200) planes of the Gd1.5Lu1.5Al2.75Ga2.25O12:Ce (PbO) (black) and Gd3Al2.75Ga2.25O12:Ce (BaO) (red) SCFs, grown onto GAGG substrates. The film/substrate lattice misfit is –0.73% and –0.3%, respectively. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

LPE Growth of Single Crystalline Film Scintillators Based on Ce3+ Doped Tb3−xGdxAl5−yGayO12 Mixed Garnets

“…Ga 3+ alloying of Tb 3 Al 5−x Ga x O 12 :Ce SCFs in the concentration range up to y = 2 leads to the shift of the TSL peaks to 407 K and substantially decreases the TSL signal in the 350-600 K range (Figure 6a, curve 2) (see also [31,36]). Gd 3+ alloying additionally shifts the TSL peak to 390 K and slightly decreases the TSL signal of Tb 1.5 Gd 1.3 Al 2.5 Ga 2.5 O 12 :Ce (PbO) SCFs in the 450-650 K high-temperature range in comparison with Gd free SCF samples (Figure 6a, curve 3).…”

“…After that, other sets of optically good quality Tb 1.5 Gd 1.5 Al 5−y Ga y O 12 :Ce SCF samples-with y values changing in the 2-3.8 range and thickness in the 10.5-22 µm range-were also successfully crystallized onto GAGG substrates from novel lead-free BaO based flux (see Figure 1, middle and right figures, and Table 1). The components of this flux have significantly smaller influence on their scintillation properties than in the case of PbO flux grown SCF scintillators [31,33,37,38]. At the same time, the high viscosity of this BaO based flux leads to formation of different structural macro-defects and strongly decreases the uniformity of SCF surface [31,33,37].…”

“…Taking into account the low temperature of SCF preparation in oxygen containing atmosphere (air), the formation of these traps can be caused mainly by the presence of Pb 2+ and Ba 2+ (from flux) and Pt 4+ (from crucible) contaminations in SCF samples. This leads to the creation of different locally non-compensated lattice defects, such as the oxygen or cation vacancies, around the mentioned impurities, which act as trapping centers [21,31,36,53,54].…”

“…This result is in good correlation with the high LY in Tb 1.5 Gd 1.5 Al 3-2.5 Ga 2-2.5 O 12 :Ce (BaO) SCFs (Table 1), due to the low Ba 2+ contamination and related with them ptrapping centers as well as to the additional elimination of the trap-related phenomena in the scintillation processes in these SCFs by Ga 3+ and Gd 3+ alloying. Thus, the Ga 3+ alloying in the concentration range y = 2-2.5 positively affects not only the scintillation properties of melt-grown mixed garnet crystals with a large concentration of antisite defects and oxygen vacancies [22][23][24] but antisite free SCF counterparts as well [31][32][33] due to burying the trap levels by the bottom of the conductive band in the Ga-containing garnets. The additional positive effect on the elimination of the trap centers in scintillation phenomena, which is observed in Tb3−xGdxAl5−xGaxO12:Ce SCF samples, is most probably caused by burying the deeper trap levels by high-energy states of Tb 3+ and Gd 3+ cations in such Tb,Gd-rich garnets [36].…”

“…The components of this flux have significantly smaller influence on their scintillation properties than in the case of PbO flux grown SCF scintillators [31,33,37,38]. At the same time, the high viscosity of this BaO based flux leads to formation of different structural macro-defects and strongly decreases the uniformity of SCF surface [31,33,37]. Such unwanted effects are also observed in the case of growing the Tb 1.5 Gd 1.5 Al 5−y Ga y O 12 :Ce SCFs from BaO based flux.…”