Scintillation properties of Tm-doped Lu3Al5O12 single crystals

Using the micro-pulling-down (μ-PD) method, Tm-doped Lu₃Al₅O₁₂ (Tm:LuAG) single crystals were grown to examine their scintillation properties. In transmittance spectra, they exhibited about 80% transparency in the wavelengths longer than 320 nm and five absorption lines due to Tm³⁺ 4f–4f transitions were observed. ²⁴¹Am α-ray excited radioluminescence spectra were measured and intense 4f–4f emission peaks were observed with the host emission. When excited by ¹³⁷Cs γ-Ray to obtain pulse height spectra, Tm 1% doped LuAG showed the highest light yield coupled with a photomultiplier (PMT) or a silicon avalanche photodiode (Si-APD). The light yield was estimated to be 5800 and 7300 photons/MeV for PMT and Si-APD, respectively. Decay time profiles consist of two exponential components and the fast and slow components are considered to be attributed to the host and the combination of the host and Tm³⁺ 4f–4f emission, respectively.     

Luminescence characteristics of LuAG:Pr and YAG:Pr single crystalline films

Emission and excitation spectra and luminescence decay kinetics were studied for Pr³⁺-doped Lu₃Al₅O₁₂ and Y₃Al₅O₁₂ single crystalline films (SCF) grown by the liquid phase epitaxy method from a PbO-based flux. The influence of lead-induced centers on their scintillation characteristics was clarified. It was found that the influence of single Pb²⁺-based centers on the characteristics of Pr³⁺ centers due to the Pb²⁺ → Pr³⁺ energy transfer was weak. However, an overlap of the emission spectra of single and dimer lead-induced centers with the emission spectrum of Pr³⁺ ions, and especially a strong overlap of the 4f–5d₁ absorption band of Pr³⁺ ions with the slow emission of localized excitons in the 290 nm band had a considerable influence on the scintillation characteristics of the Pr³⁺-doped SCF.     

Growth and luminescent properties of Lu2SiO5 and Lu2SiO5:Ce single crystalline films

Single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Lu₂SiO₅:Ce (LSO:Ce) silicates with thickness of 2.5-15 μm were crystallized by liquid phase epitaxy method onto undoped LSO substrates from melt-solution based on PbO-B₂O₃ flux. The scintillation and luminescence properties of LSO:Ce SCF were compared with the properties of LSO:Ce single crystal. The peculiarities of luminescence properties of LSO:Ce SCF in comparison with crystal analog can be due to different distribution of Ce³⁺ over the Lu1 and Lu2 positions of LSO host and are further influenced by Pb²⁺ flux-originated contamination.     

Luminescence characteristics of Ce-doped Lu1−xScxBO3 solid solution single crystals grown by Czochralski method

Solid solution crystals of Lu_1−xSc_xBO₃:Ce³⁺ (x = 0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. These crystals have high optical transmittance within wavelength concerned, except for an absorption shoulder in Lu_0.8Sc_0.2BO₃:1at%Ce³⁺ crystal from 360 to 530 nm. With the increase of Sc/Lu ratio, the excitation and emission spectra have redshift due to change of Ce³⁺ crystalline environment and the lifetime gradually increases due to the increase of emission wavelength. Efficient energy transfer from the self-trapped excitons to Ce³⁺ ions was observed. Lu_0.8Sc_0.2BO₃:1at%Ce³⁺ crystal, due to high density, short decay time, high scintillation efficiency and non-hygroscopic property, could be a promising scintillator.     

Luminescent properties of Al2O3:Ce single crystalline films under synchrotron radiation excitation

The paper is dedicated to study the luminescent and scintillation properties of the Al₂O₃:Ce single crystalline films (SCF) grown by LPE method onto saphire substrates from PbO based flux. The structural quality of SCF samples was investigated by XRD method. For characterization of luminescent properties of Al₂O₃:Ce SCFs the cathodoluminescence spectra, scintillation light yield (LY) and decay kinetics under excitation by α-particles of Pu²³⁹ source were used. We have found that the scintillation LY of Al₂O₃:Ce SCF samples is relatively large and can reach up to 50% of the value realized in the reference YAG:Ce SCF. Using the synchrotron radiation excitation in the 3.7–25 eV range at 10 K we have also determined the basic parameters of the Ce³⁺ luminescence in Al₂O₃ host.     

Crystal growth and scintillation properties of Er-doped Lu3Al5O12 single crystals

Er-doped Lu₃Al₅O₁₂ (Er:LuAG) single crystalline scintillators with different Er concentrations of 0.1, 0.5, 1, and 3% were grown by the micro-pulling-down (μ-PD) method. The grown crystals were composed of single-phase material, as demonstrated by powder X-ray diffraction (XRD). The radioluminescence spectra measured under ²⁴¹Am α-ray excitation indicated host emission at approximately 350 nm and Er³⁺ 4f-4f emissions. According to the pulse height spectra recorded under γ-ray irradiation, the 0.5% Er:LuAG exhibited the highest peak channel among the samples. The γ-ray excited decay time profiles were well fitted by the two-component exponential approximation (0.8 μs and 6-10 μs).     

Growth and characterization of Yb doped garnet crystals for scintillator application

Several concentration of Yb-doped Lu₃Al₅O₁₂ (Yb:LuAG) and Lu₃Ga₅O₁₂ (Yb:LGG) single crystals were grown by the micro-pulling-down method. The crystals were seeded-grown in the 1 1 1 direction and transparent and crack free crystals were obtained. Photoluminescence spectra and decay kinetics of these crystals were studied. Charge transfer luminescence of Yb³⁺ was observed in both crystals. Mean decay time of about 25 ns at 90 K and strong thermal quenching at room temperature was measured for Yb 5%:LuAG. Radioluminescence intensity was compared to the standard BGO sample.     

Composition engineering of single crystalline films based on the multicomponent garnet compounds

The paper demonstrates our last achievement in development of the novel scintillating screens based on single crystalline films (SCF) of Ce doped multicomponent garnets using the Liquid Phase Epitaxy (LPE) method. We report in this work the optimized content and excellent scintillation properties of SCF of Lu_3-xGd_xAl_5-yGa_yO₁₂, Lu_3-xTb_xAl_5-yGa_yO₁₂ and Tb_xGd_xAl_5-yGa_yO₁₂ garnet compounds grown by the LPE method from PbOB₂O₃ based melt-solution onto Gd₃Al_2.5Ga_2.5O₁₂ and YAG substrates.We also show that the Tb_1.5Gd_1.5Al_2.5Ga_2.5O₁₂:Ce SCF possess the highest light yield (LY) in comparison with all ever grown garnet SCF scintillators. Namely, the LY of these SCF exceeds by 3.8 and 1.85 times the LY values of the best samples of YAG:Ce and LuAG:Ce SCF scintillators, respectively. The SCF samples of the mentioned compounds show low thermoluminescence in the above room temperature range and relatively fast scintillation decay time t_1/e in the 180–200 ns range.     

Crystal growth and scintillation properties of Nd-doped Lu3Al5O12 single crystals with different Nd concentrations

Nd 0.1%, 0.5%, 1% and 3% doped Lu₃Al₅O₁₂ (Nd:LuAG) single crystals were grown in the nitrogen atmosphere by the micro-pulling down (μ-PD) method. The grown crystals had a single-phase confirmed by powder XRD analysis. In absorption spectra, some weak absorption lines due to Nd³⁺ 4f-4f transitions were observed and their intensity increased with the increase of Nd concentration. When excited by ²⁴¹Am α-ray, a broad emission peak due to defects in the host lattice at 320 nm and some sharp lines due to Nd³⁺ 4f-4f transitions at wavelength longer than 400 nm were observed. The decay time profiles of Nd:LuAG under γ-ray excitation were well approximated by two exponential function of 340-760 ns and 3-5 μs for each sample. By pulse height measurement using ¹³⁷Cs, Nd 0.5%:LuAG showed the highest light yield of 7600 ± 760 photons/MeV.     

On the relationship between emission color and Ce3+ concentration in garnet phosphors

It is known that the emission color of Ce³⁺ doped garnets is strongly redshifted at higher Ce³⁺ concentrations. In this report, we study the cause of this redshift in Lu₃Al₅O₁₂:Ce³⁺ (LuAG:Ce) phosphors. These changes in emission color with Ce³⁺ concentration are mainly attributed to a combination of inhomogenous broadening for Ce³⁺ in LuAG and energy transfer from high energy Ce³⁺ ions to low energy Ce³⁺ ions. Evidence for inhomogenous broadening and energy transfer is given through time resolved measurements. Potential reasons for inhomogenous broadening of Ce³⁺ in these phosphors are also discussed.     

Growth and scintillation properties of Yb doped aluminate, vanadate and silicate single crystals

For the purpose of quick screening for charge transfer (CT) transitions of Yb³⁺ in various hosts, (Lu_1−xYb_x)₃Al₅O₁₂ (Yb:LuAG) with x=0.05, 0.15, 0.30 and (Y_1−xYb_x)AlO₃ (Yb:YAP) with x=0.05, 0.10, 0.30 were grown by the micro-pulling-down method. (Y,Yb)VO₄ with strong wetting was grown by edge defined film-fed growth method and materials, which require moderate temperature gradient, such as Ca₈(La,Yb)₂(PO₄)₆O₂ and (Gd,Yb)₂SiO₅ were grown by Czochralski method. Strong dependence of the CT luminescence decay time and intensity on temperature was observed for Yb-doped LuAG and YAP. Super fast decay with 0.85 ns decay time was observed in Yb(30%) doped YAP at room temperature. Though the emission intensity is weak at room temperature, it exceeds several times that of PbWO₄. In addition, CT luminescence of Yb:YAP occurs at longer wavelength than in BaF₂, which enables the usage of glass-based photomultiplier for the detection. In addition, higher stopping power will be expected due to the higher density host compared with BaF₂.     

Formation of high-density scintillation ceramic from LuAG:Ce + Lu2O3 powders obtained by co-precipitation method

The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu₂O₃ (LuAG:Ce + Lu₂O₃), are described. Powders of a novel material LuAG:Ce + Lu₂O₃ were synthesized by co-precipitation method. The introduction of Lu₂O₃ into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties.     

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

Abstract

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd₃Al₅O₁₂, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd³⁺ to the activator. Ce³⁺ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out.     

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd₃Al₅O₁₂, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd³⁺ to the activator. Ce³⁺ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out.     

Intrinsic and Ce-related luminescence of YAG and YAG:Ce single crystals, single crystalline films and nanopowders

A comparative analysis of the luminescent properties of YAG and YAG:Ce nanopowders (NP) in comparison with single crystalline film (SCF) and single crystal (SC) analogues was performed under excitation by a pulsed synchrotron and X-ray radiation. It was shown that the natural defects concentration in NP was between the SC with a large (0.18–0.19 at.%) concentration of Y_Al antisite defects (AD) and SCF of these garnets where Y_Al AD were completely absent. At the same time, Ce³⁺ doped YAG NP showed luminescent properties close to those of YAG:Ce SCF.     

Scintillation properties of the Ce-doped multicomponent garnet epitaxial films

(Lu,Y,Gd)₃(Al,Ga)₅O₁₂:Ce garnet scintillator single crystalline films were grown onto LuAG, YAG and GGG substrates by liquid phase epitaxy method. Absorption, radioluminescence spectra and photoluminescence excitation, emission spectra, and decay kinetics were measured. Photoelectron yield, its dependence on amplifier shaping time and energy resolution were determined to evaluate scintillation performance. Most of the samples exhibited strong UV emission caused by trapped excitons and/or Gd³⁺ 4f–4f transition. However, emission spectrum of the best performing Gd₂YAl₅O₁₂:Ce is dominated by the Ce³⁺ fast 5d–4f luminescence. This sample has outperformed photoelectron yield of all the garnet films studied so far.     

Effective lattice stabilization of gadolinium aluminate garnet (GdAG) via Lu3+ doping and development of highly efficient (Gd,Lu)AG:Eu3+ red phosphors

Abstract

The metastable garnet lattice of Gd₃Al₅O₁₂ is stabilized by doping with smaller Lu³⁺, which then allows an effective incorporation of larger Eu³⁺ activators. The [(Gd_1?xLu_x)_1?yEu_y]₃Al₅O₁₂ (x = 0.1–0.5, y = 0.01–0.09) garnet solid solutions, calcined from their precursors synthesized via carbonate coprecipitation, exhibit strong luminescence at 591 nm (the ⁵D₀ → ⁷F₁ magnetic dipole transition of Eu³⁺) upon UV excitation into the charge transfer band (CTB) at ～239 nm, with CIE chromaticity coordinates of x = 0.620 and y = 0.380 (orange-red). The quenching concentration of Eu³⁺ was estimated at ～5 at.% (y = 0.05), and the quenching was attributed to exchange interactions. Partial replacement of Gd³⁺ with Lu³⁺ up to 50 at.% (x = 0.5) while keeping Eu³⁺ at the optimal content of 5 at.% does not significantly alter the peak positions of the CTB and ⁵D₀ → ⁷F₁ emission bands but slightly weakens both bands owing to the higher electronegativity of Lu³⁺. The effects of processing temperature (1000–1500 °C) and Lu/Eu contents on the intensity, quantum efficiency, lifetime and asymmetry factor of luminescence were thoroughly investigated. The [(Gd_0.7Lu_0.3)_0.95Eu_0.05]₃Al₅O₁₂ phosphor processed at 1500 °C exhibits a high internal quantum efficiency of ～83.2% under 239 nm excitation, which, in combination with the high theoretical density, favors its use as a new type of photoluminescent and scintillation material.     

Evaluation of characterization of rare-earth doped sesquioxide ceramic scintillators

We investigated basic optical and scintillation properties of pure Y₂O₃, Tm³⁺-doped Y₂O₃, pure Lu₂O₃ and Nd³⁺-doped Lu₂O₃ transparent ceramics made by a sintering method. All ceramic samples showed 60–80% transparency, and some absorption bands due to Nd³⁺ 4f–4f transition were observed in Nd³⁺:Lu₂O₃ ceramic. Both Tm³⁺:Y₂O₃ and Nd³⁺:Lu₂O₃ ceramics showed sharp luminescence lines corresponding to the 4f–4f transition under 285 nm (Tm³⁺:Y₂O₃) and 340 nm (Nd³⁺:Lu₂O₃) excitation. The photoluminescence decay times were calculated to be about 24 μs for Tm³⁺:Y₂O₃ and 1 μs for Nd³⁺:Lu₂O₃, respectively. In radioluminescence measurements, Tm³⁺ and Nd³⁺ 4f–4f luminescence were observed for Tm³⁺-doped Y₂O₃ and Nd³⁺-doped Lu₂O₃ ceramics under ²⁴¹Am 5.5 MeV α-ray excitation. Finally scintillation light yield was investigated with pulse height analysis.     

Shaped single crystal growth and scintillating application of Yb:(Gd,Lu)3(Ga,Al)5O12 solid solutions

Shaped single crystals of (Yb_0.05Lu_xGd_0.95−x)Ga₅O₁₂ (0.0x0.9) and Yb_0.15Gd_0.15Lu_2.7(Al_xGa_1−x)O₁₂ (0.0x1.0) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃(Ga,Al)₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect––host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.