Recent R&amp;D Trends in Inorganic Single‐Crystal Scintillator Materials for Radiation Detection

Nikl, M.; Yoshikawa, Akira

doi:10.1002/adom.201400571

Cited by 622 publications

(405 citation statements)

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“…6b scintillators. 24 The emission at Ce 3+ and Eu 2+ involves the transition of an electron from the 5d level to the 4f level (see Fig. 7).…”

Section: 57mentioning

confidence: 99%

“…For example, new efficient red phosphors with suitable emission wavelengths are highly desirable for producing warm white light from LEDs; [21][22][23]6,14 scintillators with improved energy resolutions are sought for gamma-ray spectroscopy. 24 Theoretical calculations can be useful for searching for new materials and optimizing existing materials. The important material properties that need to be calculated may differ for different applications.…”

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confidence: 99%

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Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns 2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, which can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn 4+ Luminescence of materials when excited by photons or ionizing radiation is the foundation for numerous technologies, such as energy efficient lighting (fluorescent lamps and white LEDs), laser, medical imaging, and nuclear materials detection.1-3 Efficient luminescence in semiconductors and insulators usually relies on the localization of excited electrons and holes at certain impurities, which act as luminescence centers (or activators). An activator can trap electrons and holes for efficient radiative recombination and is the essential component of a phosphor or scintillator material. The commonly used activators are typically multivalent ions, which can insert multiple electronic states inside the bandgap of the host material. 45 Good examples of the multivalent ions that can act as luminescent centers are rare-earth ions (e.g., Ce 3+ , Eu 2+ ), 6-11 transition metal ions (e.g., Cr 3+ , Mn 4+ ), [12][13][14][15][16][17] and ns 2 ions (ions with outer electron configuration of ns 2 , such as Tl + , Sn 2+ ). 18-20Energy efficiency is critically important for phosphors used for lighting. To suppress the energy loss through nonradiative recombination, a phosphor is excited by directly exciting activators, not the host (see Fig. 1a). The excitation energy is less than the bandgap energy of the host but is large enough to excite the activator. Since the excitation occurs locally at the activator, the chance for the excited activator to interact with nonradiative recombination centers, such as deep defects, is small. This is important for achieving high quantum efficiencies for phosphors. In scintillators used for detecting ionizing radiation, the radiation creates charge carriers in the valence and conduction bands of the host, which are subsequently trapped by activators, leading to radiative recombination (see Fig. 1b). In scintillators, a portion of the charge carriers need to travel a certain distance before being trapped by the activators, which ...

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“…6b scintillators. 24 The emission at Ce 3+ and Eu 2+ involves the transition of an electron from the 5d level to the 4f level (see Fig. 7).…”

Section: 57mentioning

confidence: 99%

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confidence: 99%

Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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“…Within the last two decades, a number of excellent scintillators based on Ce 3+ and Pr 3+ -doped materials, together with truly novel nanoscintillators, nanocomposites, and phase-separated material systems, have been discovered and studied in depth. [1][2][3][4][5][6][7][8] This high R&D activity in the scintillator fi eld was triggered by the pressing needs of modern medical imaging and radiotherapy, of high-energy physics, homeland security, and environmental applications. Among them, Cedoped Lu 3 Al 5 O 12 (LuAG:Ce) aluminum garnets have attracted much attention because of their relatively high density of 6.73 g cm −3 , 5d -4f electric dipole allowed radiative transition of Ce 3+ with emission at around 500-550 nm, fast scintillation response of about 60 ns, and high theoretical light yield (LY) value of 60000 photons/MeV.…”

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confidence: 99%

Towards Bright and Fast Lu₃Al₅O₁₂:Ce,Mg Optical Ceramics Scintillators

Liu

Mareš

Feng

et al. 2016

Advanced Optical Materials

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needed. Within the last two decades, a number of excellent scintillators based on Ce 3+ and Pr 3+ -doped materials, together with truly novel nanoscintillators, nanocomposites, and phase-separated material systems, have been discovered and studied in depth. [1][2][3][4][5][6][7][8] This high R&D activity in the scintillator fi eld was triggered by the pressing needs of modern medical imaging and radiotherapy, of high-energy physics, homeland security, and environmental applications. Among them, Cedoped Lu 3 Al 5 O 12 (LuAG:Ce) aluminum garnets have attracted much attention because of their relatively high density of 6.73 g cm −3 , 5d -4f electric dipole allowed radiative transition of Ce 3+ with emission at around 500-550 nm, fast scintillation response of about 60 ns, and high theoretical light yield (LY) value of 60000 photons/MeV. [ 9,10 ] It was found that LuAG:Ce single crystal containing 0.55 at% Ce 3+ ions prepared by Bridgman technique is a highly competitive scintillator displaying a LY of about 26000 photons/MeV with a shaping time of 1.5 μs, close to that of Lu 2 SiO 5 :Ce (LSO:Ce). [ 11 ] Based on the understanding of defect chemistry, an effective bandgap engineering approach was successfully applied to the LuAG system. Multicomponent garnets, featuring a balanced admixture of Gd and Ga cations in the Lubased garnet structure, form a new family of materials with an amazingly high light yield up to 58000 photons/MeV, a value exceeding that of the best Lu 2-x Y x SiO 5 :Ce (LYSO:Ce) materials by about 40%. [12][13][14][15] Therefore, oxides based on garnet structure are presently considered as competitive candidates for advanced scintillation applications.However, the low segregation coeffi cient of Ce 3+ ions in the LuAG lattice is detrimental for the growth of homogeneously doped large LuAG:Ce single crystals, especially for high Ce 3+ concentrations (Ce 3+ > 0.2 at%). [ 16 ] It was also noticed that Lu Al antisite defects (AD) can severely deteriorate the scintillation characteristics of LuAG:Ce single crystals by acting as shallow traps, thus delaying the energy transport to the Ce 3+ emission centers. [ 17 ] Therefore, extensive research has recently been aimed at the preparation of ceramic analogues, which are characterized by lower preparation temperatures, more uniform doping, and lower cost. One point to consider is that during The choice of sintering agent appears critical to achieve both high optical transparency and scintillation performance. In this work, the optical investigations coupled with X-ray absorption near-edge spectroscopy evidence the benefi cial role of MgO sintering agent. Mg 2+ co-dopants in ceramics drive the partial conversion of Ce 3+ to Ce 4+ . The Ce 4+ center, however, does not impair the scintillation performance due to its capability to positively infl uence the scintillation process. The importance of simultaneous application of such co-doping and annealing treatment is also demonstrated. With 0.3 at% Mg, our ceramics display a light yield of ≈25000 photons/MeV wit...

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“…The absorption spectrum for the crystal grown from a presynthesized charge in air is also represented in the figure to understand the role of the multivalent states of cerium ions. The increased absorption at higher energies may be assigned to the charge transfer transition from O 2-to Ce ions [16]. It suggests an excessive presence of cerium ions in the tetravalent state (+4) in the material synthesized in air.…”

Section: Experimental Techniquesmentioning

confidence: 97%

Improvement of the scintillation properties of Gd₃ Ga₃ Al₂ O₁₂ :Ce,B single crystals having tailored defect structure

Tyagi

Singh

et al. 2015

Phys. Status Solidi RRL

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A novel approach is reported to minimize various defect centers in Ce doped Gd3Ga3Al2O12 single crystals to improve the scintillation properties. The crystals of Gd3Ga3Al2O12 codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a 137Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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Recent R&D Trends in Inorganic Single‐Crystal Scintillator Materials for Radiation Detection

Cited by 622 publications

References 242 publications

Using DFT Methods to Study Activators in Optical Materials

Using DFT Methods to Study Activators in Optical Materials

Towards Bright and Fast Lu₃Al₅O₁₂:Ce,Mg Optical Ceramics Scintillators

Improvement of the scintillation properties of Gd₃ Ga₃ Al₂ O₁₂ :Ce,B single crystals having tailored defect structure

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Recent R&D Trends in Inorganic Single‐Crystal Scintillator Materials for Radiation Detection

Cited by 622 publications

References 242 publications

Using DFT Methods to Study Activators in Optical Materials

Using DFT Methods to Study Activators in Optical Materials

Towards Bright and Fast Lu3Al5O12:Ce,Mg Optical Ceramics Scintillators

Improvement of the scintillation properties of Gd3 Ga3 Al2 O12 :Ce,B single crystals having tailored defect structure

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Towards Bright and Fast Lu₃Al₅O₁₂:Ce,Mg Optical Ceramics Scintillators

Improvement of the scintillation properties of Gd₃ Ga₃ Al₂ O₁₂ :Ce,B single crystals having tailored defect structure