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Encarnación G. Víllora, [Yueshen Zhou](https://orcid.org/0009-0009-5327-9731), Kenichi Watanabe, [Kiyoshi Shimamura](https://orcid.org/0000-0001-6502-8731)

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[Scintillation efficiency of Tb:YTaO<sub>4</sub> single crystals](https://mdr.nims.go.jp/datasets/c08b7317-c5a5-4578-a3b2-15db68bd1c86)

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Scintillation efficiency of Tb:YTaO4 single crystalsApplied PhysicsExpress      LETTER • OPEN ACCESSScintillation efficiency of Tb:YTaO4 single crystalsTo cite this article: Encarnación G. Víllora et al 2025 Appl. Phys. Express 18 032002 View the article online for updates and enhancements.You may also likeNonvolatile magneto-thermal switchingdriven by vortex trapping in commercial In-Sn solderPoonam Rani, Takumi Murakami, YutoWatanabe et al.-Physical reservoir computing withgraphene-based solid electric double layertransistor and the information processingcapacity analysisHina Kitano, Daiki Nishioka, KazuyaTerabe et al.-Recovery of plasma-induced defects inSiO2/Si stack: defect activation andhydrogen’s effectsShota Nunomura, Takayoshi Tsutsumi andMasaru Hori-This content was downloaded from IP address 144.213.253.16 on 17/03/2025 at 03:38https://doi.org/10.35848/1882-0786/adb89fhttps://iopscience.iop.org/article/10.35848/1882-0786/adb6eehttps://iopscience.iop.org/article/10.35848/1882-0786/adb6eehttps://iopscience.iop.org/article/10.35848/1882-0786/adb6eehttps://iopscience.iop.org/article/10.35848/1882-0786/adb19bhttps://iopscience.iop.org/article/10.35848/1882-0786/adb19bhttps://iopscience.iop.org/article/10.35848/1882-0786/adb19bhttps://iopscience.iop.org/article/10.35848/1882-0786/adb19bhttps://iopscience.iop.org/article/10.35848/1882-0786/adb82ehttps://iopscience.iop.org/article/10.35848/1882-0786/adb82ehttps://iopscience.iop.org/article/10.35848/1882-0786/adb82ehttps://iopscience.iop.org/article/10.35848/1882-0786/adb82ehttps://pagead2.googlesyndication.com/pcs/click?xai=AKAOjst0qn5muKyKUYGIpHTNL65SRrM4Qc7OGcVvCJQnVUDzZtUFgsUfTQL20Fo4IFDq1e9ms6PFh0i_pCWhQabYKM4e8TS7ZXUAgSq11iw2875oTBhWmUGqzE3YKLebUeDqXPk4c8iTL2gpCr7JO3QJ5oMdJG2UUE83LqRG3FJJi0ka3P84ihEnKnb9Bw29lyrfEKQrj6sa2DjJNtmvwW-YWTOGxRaWzvrY7a72wFukfW7eu2zgJ1EnQNglmXCoziJmYge0FSLUUQo4am38lwldZ6sdsiuthv0QJaJGhyxoZ4kTw8sLdCYLL6YaQgdoO1SQPS9zz5vWo6VUsfEDWYAoXKDjvvnMzBWaEBjxiMALAht52AM&sig=Cg0ArKJSzDaKNZ6EMfd6&fbs_aeid=%5Bgw_fbsaeid%5D&adurl=https://ecs.confex.com/ecs/248/cfp.cgi%3Futm_source%3DIOP%26utm_medium%3Dbanner%26utm_campaign%3DIOP_248_abstract_submission%26utm_id%3DIOP%2B248%2BAbstract%2BSubmissionScintillation efficiency of Tb:YTaO4 single crystalsEncarnación G. Víllora1*, Yueshen Zhou1,2, Kenichi Watanabe3, and Kiyoshi Shimamura1,2*1National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan2Waseda University, 3-4-1 Ookubo, Shinjuku, Tokyo, 169-8555, Japan3Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan*E-mail: VILLORA.Garcia@nims.go.jp; SHIMAMURA.Kiyoshi@nims.go.jpReceived February 16, 2025; revised February 18, 2025; accepted February 19, 2025; published online March 12, 2025Environmentally friendly scintillators are demanded to substitute CdWO4 single crystal for X-ray imaging. Tb3+:YTaO4 single crystals are apromising candidate with a high stopping power, green emission matching to photodiodes, and a small afterglow. This study demonstrates that thelight yield of Tb3+:YTaO4 scintillators is ∼ 24,000 ph/MeV. Furthermore, the fluorescence lifetime, ∼ 970 μs, though shorter than in other oxides, isclose to the theoretical prediction by Judd-Ofelt analysis, indicating a high emission quantum efficiency of the Tb3+ activator. As the scintillationlifetime is shorter due to non-radiative decay, a potential light yield increase to 33,000 ph/MeV is estimated.© 2025 The Author(s). Published on behalf of The Japan Society of Applied Physics by IOP Publishing LtdSupplementary material for this article is available onlineCdWO4 (CWO) is one of the earliest found andimplemented scintillators still used for high-energyX-ray radiography applications.1) Its high density(ρ = 7.9 g cm−3) and stopping power (estimated asρ*Zeff4 = 134 × 106, with an effective atomic numberZeff = 64.2), low afterglow (∼ 0.01% @ 20ms), andradiation resistance are unique. Though its light yield (LY)is moderate (∼14,000 ph MeV−1), its intrinsic visibleemission matches well with the spectral sensitivity ofSi-photodiodes (Si-PDs). The possibility of producing trans-parent CWO single crystals using the standard Czochralskigrowth technique is also crucial for the device implementa-tion in bulk form. Despite various advantages, the toxiccharacter of Cd is a fundamental drawback since environ-mentally friendly materials are being demanded in evolvingworldwide directives. Therefore, there is a need to developalternative materials to substitute CWO.Terbium is one of the typical dopants in phosphors andscintillators. Its dominant green luminescence is used influorescent displays, X-ray and neutron imaging, radiationdosimetry, lasers, biological markers, etc.2–12) In the parti-cular case of scintillators, Tb3+ represents an activator ionwith a remarkable emission quantum efficiency (QE) in thevisible, matching well the spectral sensitivity of Si-PDs.Furthermore, since its decay is comparatively slow, with alifetime in the millisecond order, it is suitable for applicationswhere sensitivity and spatial resolution, rather than dynamicresponse, are essential. The most representative example,which has become a commercial product, is Tb:Gd2O2S(Tb:GOS).3,5,13–15) It exhibits a high density and stoppingpower of Tb:GOS (7.34 g cm−3 and 102x106, respectively), anda high LY. However, only translucent ceramics can be synthe-sized, limiting its use to thin film applications. Recently, it hasbeen shown that among the heavy tantalates, doped YTaO4(YTO) transparent single crystals are a promising alternative toCWO,16,17) particularly when doped with Tb. With a relativelyhigh activator concentration, 15%Tb:YTO compromises highdensity and stopping power (7.76 g cm−3 and 129 × 106,respectively) with an emission maximum in X-ray luminescence(XRL). The radioluminescence LY of Tb:YTO, however, hasn’tbeen determined yet because the decay of Tb3+ ions is too slowto carry out a standard pulse-height analysis (PHA).This study aims to determine the LY of Y1-xTbxTaO4 (Tb:YTO, or 100·x%Tb:YTO) single crystals grown by theFloating zone (FZ) technique. Pulse area integration18)(PAI) is used to evaluate the LY instead of standard PHA.Furthermore, to assess the emission efficiency of Tb3+activator ions, photoluminescence (PL) decay measurementsupon intraatomic and conduction band excitation are mea-sured and compared with theoretical values obtained throughJudd-Ofelt (JO) analysis. By further comparison with theXRL decay, the scintillation efficiency is estimated.Tb:YTO crystals were grown by the FZ technique using afour-xenon-lamp furnace from Crystal Systems Corp. Thecompositions were varied along the full solid-solution range,from low Tb concentrations up to fully substituted TbTaO4(TTO). High-purity (4 N) oxides (Y2O3, Ta2O5, and Tb4O7)were weighed in stoichiometric ratios and mixed. Feed rodswere prepared by isostatic pressing at 300MPa and subse-quent sintering at 1300 °C for 10 h under a reducingAr+3%H2 atmosphere. Further growth details and growncrystals are shown in a previous publication.17) Here, itshould be noted that the actual Tb concentration in crystalsagreed with the nominal one according to energy-dispersiveX-ray spectroscopy.LY measurements were carried out by a digital PAI using asetup specially designed for scintillators with a decay time inthe millisecond order.18) 137Cs isotope was used as theexcitation source, which emits 662 keV gamma photonsupon intermediate beta decay to metastable 137Ba of only153 s half-life. The difference in spectral sensitivity of thephotomultiplier for the emissions of Tb:YTO and BGOreference was corrected with the factor 2.026. Excitationand emission PL spectra were recorded with a Jasco-8600DSfluorescence spectrometer. PL decay measurements wereobtained with a setup consisting of an oscilloscope, achopper, a Fluorolog Jobin-Yvon photospectrometer fromHoriba, and an R928 Hamamatsu photomultiplier. Thecontinuous excitations sources were pulsed with a singlenarrow slit blade rotating at a frequency of 11.5 Hz. ThisContent from this work may be used under the terms of the Creative Commons Attribution 4.0 license. Any further distribution of thiswork must maintain attribution to the author(s) and the title of the work, journal citation and DOI.032002-1© 2025 The Author(s). Published on behalf ofThe Japan Society of Applied Physics by IOP Publishing LtdApplied Physics Express 18, 032002 (2025) LETTERhttps://doi.org/10.35848/1882-0786/adb89fhttps://crossmark.crossref.org/dialog/?doi=10.35848/1882-0786/adb89f&domain=pdf&date_stamp=2025-03-12mailto:VILLORA.Garcia@nims.go.jpmailto:SHIMAMURA.Kiyoshi@nims.go.jphttps://doi.org/10.35848/1882-0786/adb89fhttps://creativecommons.org/licenses/by/4.0/https://doi.org/10.35848/1882-0786/adb89fguaranteed a long enough decay time between excitationpulses but promoted a slow rise time. While reabsorption wasnegligible due to the short penetration depth of excitationsources, emissions with wavelengths longer than that ofexcitation were selected with the spectrometer to preventartifacts from scattered light. The 546 nm emission (5D4 →7F5) decay was measured upon, firstly, intraatomic Tb3+excitation (7F6 →5D4 transition) with a 488 nm laser pointer,and, secondly, excitation in the conduction band of a hostwith a 222 nm lamp from Quark Technology (eVIO-100).The 437 nm emission (5D3 →7F4) decay was measured uponintraatomic Tb3+ excitation (7F6 →5D3 transition) with a UVLED (LED-UV365P from OptoCode Corp.). Transmittancemeasurements for the JO analysis were performed with aJasco V-570 UV–vis-NIR spectrometer and a PerkinElmerSpectrum One FT/IR. The dispersion of the refractive index nfrom 231 to 800 nm was determined with an OPTM-A1 fromOtsuka Electronics on a random crystal surface. It should benoticed that though the monoclinic crystals are opticallybiaxial, the anisotropy is supposed to be relatively small inthese crystals.16) Within the measured range (231 to 800 nm)n didn’t show any systematical change with the Tb concen-tration, and even agreed well with reported values for YTO19)and GdTaO420) tantalates. Therefore, the n values in the nearIR range were taken from the literature.The LY of Tb:YTO crystals as a function of Tb concen-tration is shown in Fig. 1. The PAI analysis was carried outby comparison with the energy distribution response of aBi4Ge3O12 (BGO) single crystal of 8,000 ph/MeV LY underthe same experimental conditions. Up to 20% Tb content, theLY of all samples lies between 20,000 and 26,000 phMeV−1, i.e. within the ∼ 10% standard deviation inherentto the PAI technique. This value is about 70% higher thanthat of a standard CWO. Beyond 25%Tb concentration, theLY rapidly decreases, and reliable measurements above 35%Tb couldn’t be conducted under the same conditions. The LYdrop with Tb concentration was equally observed in priormeasurements of integrated XRL spectra, and it was attrib-uted to quadrupole-quadrupole interactions between neigh-boring Tb3+ ions.17) Unlike former XRL measurements, thereis no noticeable improvement after annealing under areducing atmosphere, nor is there a clear maximum LY at15%Tb concentration. If the annealing effect is only super-ficial, the difference between both results might be attributedto the largely differing penetration depth of both excitationsources. While 8 keV Cu X-rays are absorbed at the surface(within < 100 μm) in former XRL, gamma-rays in currentPAI pass through the sample (penetration depth ∼ 10 cm).Therefore, the homogeneity of the annealing process requiresa further detailed investigation.The PL decay of Tb3+ ions upon dissimilar excitationpaths, namely intraatomic @ 488nm and through host @222nm, was investigated to gain more insight into theemission efficiency. The distinction between both excitationwavelengths is understandable when considering the PLspectra. Figure 2(a) shows the excitation and emission PLof 15%Tb:YTO and TTO along with the spectra of the YTOhost reference. At the same time, Fig. 2(b) illustrates theTb3+ energy levels relative to the valence and conductionbands of the YTO host. As found by XPS,21) the valenceband of YTO, mainly determined by O-2p orbitals, broadensby the appearance of Tb3+ energy levels after Tb incorpora-tion, where the ground state 7F6 represents the new valenceband maximum. As a result, the 5.0 eV bandgap of YTOnarrows to the 4.0 eV one of TTO. Consequently, threeexcitation possibilities can be distinguished: (1) a pure Tb3+intraatomic absorption at 488 nm, the well-known 7F6 →5D4transition, (2) a Tb3+-host absorption peaking at 280 nm, thetransition 7F6 → Ta-5d from the Tb3+ ground level at thevalence band maximum to the conduction band bottom, and(3) the host absorption peaking at 222 nm, in good corre-spondence with the non-doped YTO excitation maximum.The results of PL decay measurements are shown in Fig. 3.The PL decay curves are characterized by a single exponentialcomponent, independently of both the excitation wavelengthand the Tb concentration. The decay curves of 15%Tb:YTOand TTO with the corresponding fitting are shown as examplesin Fig. 3(b). This finding contrasts with the double exponentialdecay observed in previously measured XRL curves.17) Thelifetime dependences on Tb content upon the host andintraatomic excitation are very similar to the former depen-dence of the slow XRL component. However, their absolutevalues are different. The three curves exhibit the longestlifetime for the 15%Tb:YTO crystal, indicating that the non-(a) (b)Fig. 1. (a) Light yield of Tb:YTO crystals as a function of Tb concentration. (b) 137Cs γ-ray integrated pulse area response of representative 10%Tb:YTOand reference BGO.032002-2© 2025 The Author(s). Published on behalf ofThe Japan Society of Applied Physics by IOP Publishing LtdAppl. Phys. Express 18, 032002 (2025) E. G. Víllora et al.radiative recombination losses are minimal at this concentra-tion. This finding completely correlates with the maximum LYobserved in integrated XRL measurements. Following thesame logic, the lifetimes decrease when the quadrupole-quadrupole Tb interactions quench the luminescence at higherconcentrations. The following observations are made bycomparison of the absolute values: (1) in the low Tbconcentration range, the lifetimes upon intraatomic and hostexcitations are the same, indicating an optimum electronictransfer from the conduction band to the Tb3+ activator ions.(2) On the contrary, in the high Tb concentration range, thelifetime upon excitation into the conduction band is higher,indicating that the probability of non-radiative recombinationof excited electrons is lower. Under the hypothesis of ahomogeneous excitation of all Tb3+ centers upon intraatomicexcitation, the latter observation indicates that the conductionband favors the transfer of excited electrons to radiative Tb3+centers, lessening the transfer to non-radiative ones. (3) Uponexcitation in the upper energy bands by high-energy ionizingradiation (X- or γ-rays), there is a general decrease in lifetimefor all Tb concentrations, caused by non-radiative recombina-tion losses. In other words, the LY can be improved. Toevaluate the scintillation potential of Tb:YTO crystals, adetailed investigation of the theoretical transition probabilitiesA, branching ratios β, and radiative lifetimes τR of excitedTb3+ energy levels in Tb:YTO crystals was approached for thefirst time by the JO formalism.In the free-ion approximation, the 4 f n electric dipoletransition (ED) intensity from an initial ground state ofquantum numbers (S, L, J) to an excited state of quantumnumbers (S’, L’, J’) is theoretically estimated by( ) | [ ] ‖ ‖ [ ] | ( )( )US J J f SL J f S L J; , 1tEDttn n2,4,62å¢ = W á ¢ ¢ ¢ñ=where U(t) are the host independent doubly reduced matrixelements of rank t, and Ωt (t = 2, 4, 6) the JO parametersspecific to the material. The JO analysis relies on accuratelydetermining the absorption spectrum α(λ). For each state(or manifold m), the mean wavelength is calculated as̄ ( ) ( )/d dò òl la l l a l l= , the absorption cross-section as̄ ( ) [ ]/d Tbòa l lG = , and the resulting line strength as( )¯̄ ( )Sch Jenn3 2 1832, 2m 3 2 22p l=++G⎛⎝⎞⎠where n is the refractive index, c the speed of light, and h thePlanck’s constant. The JO parameters are determined by the(a) (b)Fig. 2. (a) Excitation & emission PL spectra of 15%Tb:YTO and TTO, together with YTO host reference. (b) Schematic energy diagram of Tb3+:YTO.(a) (b)Fig. 3. (a) Lifetime of Tb:YTO crystals upon excitation in the UV (host @ 222 nm) & visible (intraatomic @ 488 nm) as a function of Tb concentration.(b) Decay curves of 15%Tb:YTO and TTO upon UV excitation. *17).032002-3© 2025 The Author(s). Published on behalf ofThe Japan Society of Applied Physics by IOP Publishing LtdAppl. Phys. Express 18, 032002 (2025) E. G. Víllora et al.least-square fitting that minimizes the difference betweenthe theoretical (Eq. (1)) and experimental (Eq. (2)) linestrengths.22)Though magnetic dipole interactions (MD) are generallyorders of magnitude smaller than ED ones, their contributionsare sometimes non-negligible. Their line strengths are calcu-lated as.23)( ) | [ ] ‖ ‖ [ ] | ( )S J J f SL J L S f S L J; 2 , 3MD Bn n2 2m¢ = á + ¢ ¢ ¢ñand the resulting transition probabilities A(J;J’) as( )( ) ¯ ( )A J Jeh JnnS n S;643 2 123, 4ED MD4 232 22pl¢ =¢ +++⎜ ⎟⎡⎣⎢⎛⎝⎞⎠⎤⎦⎥The radiative lifetime τR and the emission branching ratio βof an excited state J’ are obtained from the A(J;J’) as( )( )A J J1;5RJt =å ¢and( )( )( )A J JA J J;;. 6Jb =¢å ¢The transmittance spectra of representative crystals,namely 15% and 55%Tb:YTO, and the fully substitutedTTO, were measured. The derived absorption coefficient ofTb3+ as a function of wavelength in the UV-visible-near IR isshown in Fig. 4, where the corresponding Tb3+ 4 f n excitedstates are indicated. The absorption cross-sections werecalculated considering the Tb concentrations of the crystals(20.33, 73.89, and 133.00 × 10−20 atoms/cm3 for 15%, 55%,and 100%Tb, respectively).The experimental and JO calculated line strengths aresummarized in Table I for three well-differentiated Tb concen-trations: 15% and 55%Tb:YTO, and fully substituted TTO. Theleast-square fittings of the absorption bands are relatively good,as indicated by the small δ values. The obtained JO parametersΩt (t = 2, 4, and 6) are very similar for the evaluated samplesdespite the largely varying Tb content, contrasting with the shiftsobserved with composition.24–28) The Ωt dependences observedin glasses are attributed to the modification in the local structurewith the composition, the Ω2 being particularly dependent oncovalency and asymmetry .25,27) As in the case of Tb:YTO, theTb site remains invariant along the whole solid solution betweenYTO and TTO compounds, it is reasonable that Ωt arecomparable within the errors of the semiempirical JO approx-imation. The calculated Ωt are relatively close to those of a Tb-doped lithium borate glass.26)Table II summarizes the JO estimation of transition prob-abilities, branching ratios, and radiative lifetimes of the meta-stable 5D3 and5D4 energy levels of Tb3+ for the representativecase of 15%Tb:YTO. For comparison, the experimental life-times and branching ratios of 1% and 15%Tb:YTO obtained byPL are also given. For the greenish emission from the 5D4 level,the agreement between experimental and calculated results isreasonably good. Instead, the approximation of the bluishemission from the upper 5D3 level is less accurate. The PLemission and decay stemming from the 5D3 level are displayedin Fig. 5. There is a noteworthy difference in the most intensetransitions; for 1%Tb:YTO, it is the 5D3 → 7F6, while theestimated is the 5D3→7F4. Furthermore, the fluorescent lifetimeτPL, 440 μs from a single exponential decay, is 70% ofthe radiative τR with a value of 630 μs. The suppression ofthe bluish emission at relatively low Tb concentrations is well-known and attributed to a cross-relaxation process,29–31) asshown in the scheme of Fig. 2(b). The energy is transferred bythe emission 5D3 → 5D4 from an excited Tb3+ ion and thesubsequent absorption 7F6 → 7F0 at a neighboring one inthe ground state. This process is resonant and accelerates thedepopulation of the 5D3 level, quenching the bluish emission byshortening its lifetime. Meanwhile, it favors the increase in thegreenish emission by the population of the 5D4 level.31,32)Additionally, it should be noticed that the observation of thebluish emission in Tb:YTO crystals is indicative of a homo-geneous Tb distribution in the rare earth site since the presenceof Tb clusters would quench the emission.A comparison of the JO calculation with other Tb-dopedsingle crystals is given in Table III. Tb-fluorides exhibitlower Ω2 values and longer lifetimes than Tb-oxides. Thesmall covalency characteristic of fluorides causes the low Ω2.The Ωt values of Tb:YTO crystals are within the typical rangefor oxides, however, their lifetimes are relatively shorter. TheΩ2 of TbAlO3 seems to be overestimated, particularly whencompared with the analogous to our case Tb:YAlO3. Themeasured PL decay of Tb:YTO crystals in the lower concentra-tion range is pretty close to the radiative one estimated by JO,(a) (b)Fig. 4. Absorption coefficient of Tb3+ in the (a) UV-visible and (b) near IR wavelength regions of 15% and 55%Tb:YTO, and TTO crystals.032002-4© 2025 The Author(s). Published on behalf ofThe Japan Society of Applied Physics by IOP Publishing LtdAppl. Phys. Express 18, 032002 (2025) E. G. Víllora et al.Table I. Measured and calculated average absorption line strengths of 15%Tb:YTO, 55%Tb:YTO, and TTO. Derived JO parameters Ω t and root-mean-square deviations δ.[Tb3+] = 15% Tb:YTO 55% Tb:YTO TTOLine strength Line strength Line strengthTransition 7F6 → l̄ (nm) (10−20 cm2) l̄ (nm) (10−20 cm2) l̄ (nm) (10−20 cm2)S(exp.) S(calc.) S(exp.) S(calc.) S(exp.) S(calc.)5H7+5D0 319.5 0.0898 0.0866 319.6 0.0671 0.0815 319.6 0.0653 0.07545G2+5G3+5L6+5L7+5L8 342.0 0.1232 0.1262 342.6 0.0000 0.1254 343.2 0.0931 0.11315L9+5G4+5D2 352.8 0.1324 0.1832 352.4 0.0922 0.183 352.2 0.0767 0.16385G5+5L10 359.4 0.0961 0.2397 358.8 0.1289 0.2382 358.1 0.1024 0.21425L10+5G6 369.6 0.1208 0.2471 369.7 0.1098 0.2455 370.0 0.0701 0.21985G6+5D3 378.2 0.1740 0.0689 378.1 0.1708 0.0678 376.5 0.1752 0.05965D4 487.1 0.0351 0.0135 486.6 0.0374 0.0127 487.8 0.0270 0.01167F0+7F1+7F2 1877.4 3.2801 3.214 1873.0 3.2730 3.2116 1856.2 2.8121 2.87097F3 2263.0 1.9301 2.087 2261.4 1.9921 2.1123 2252.2 2.0799 1.78977F4 2958.9 3.2971 3.2152 2956.6 3.2608 3.1992 2967.3 2.5164 2.67327F5 4565.3 6.1340 6.1472 4539.8 5.7463 5.7558 4606.3 5.1599 5.1335Ω2 (× 10−20 cm2) = 6.6 ± 0.4 5.7 ± 0.4 5.6 ± 0.5Ω4 (× 10−20 cm2) = 3.5 ± 0.3 3.6 ± 0.3 2.8 ± 0.3Ω6 (× 10−20 cm2) = 3.08 ± 0.11 3.07 ± 0.11 2.76 ± 0.15δ (× 10−20 cm2) = 0.104 0.105 0.146Table II. Calculated line strengths S, transition probabilities A, branching ratios β, and radiative lifetimes τR of 5D3 and5D4 energy levels of Tb3+ for therepresentative 15%Tb:YTO crystal. Experimental branching ratios βPL and fluorescent lifetimes τPL of 1% and 15%Tb:YTO crystals are given for comparison.Transition λ (nm) S (x10−20 cm2) AED (s−1) AMD (s−1) β τR (ms) 1%Tb:YTO 15%Tb:YTOβPL τPL (ms) βPL τPL (ms)5D3 →5D4 1725.9 0.4867 83.16 60.201 0.090 —7F0 484.7 0 0 0 0.000 —7F1 479.5 0.0122 108.375 0 0.068 0.009 —7F2 469.3 0.0184 175.028 40.747 0.135 0.019 —7F3 454.7 0.0085 89.472 2.208 0.058 0.035 —7F4 435.4 0.0433 527.259 144.961 0.421 0.276 —7F5 412.8 0.0183 265.367 0 0.166 0.261 —7F6 380.8 0.0052 98.571 0 0.062 0.63 0.401 0.440 — —5D4 →7F0 673.9 0.0061 14.235 0 0.016 0.016 0.0177F1 664 0.0089 21.963 0 0.025 0.019 0.0207F2 644.6 0.0092 24.778 0 0.028 0.008 0.0097F3 617.4 0.0187 57.674 14.31 0.082 0.092 0.0927F4 582.3 0.0136 50.307 0.453 0.058 0.116 0.1157F5 542.6 0.1047 485.517 122.756 0.691 0.578 0.5767F6 488.6 0.0135 87.746 0 0.100 1.14 0.172 0.929 0.171 0.976(a) (b)Fig. 5. (a) PL emission and (b) decay from the Tb3+ 5D3 excited state of 1%Tb:YTO.032002-5© 2025 The Author(s). Published on behalf ofThe Japan Society of Applied Physics by IOP Publishing LtdAppl. Phys. Express 18, 032002 (2025) E. G. Víllora et al.suggesting that the emission QE of the Tb3+ center is quitehigh. The fluorescence QE η can be approximately estimatedwith the theoretical radiative decay asɳ ( ). 7measuredRtt=Therefore, for the optimum 15%Tb:YTO, with τPL & τXRLvalues of 976 and 730 μs, respectively, the ηPL and ηXRL are∼86% and 64%, respectively. It is noteworthy that thefluorescence efficiency in Tb:YTO is quite high up tothe concentration quenching above 20%Tb, suggesting thatthe resonant energy transfer is negligible.31) From this it canbe deduced that the scintillation LY has a potential improve-ment of about ∼36%, increasing from ∼24,000 ph/MeV to33,000 ph MeV−1, if the non-radiative recombination centersthat quench the scintillation are eliminated.The present study evaluates the scintillation LY of FZ-grownTb:YTO transparent single crystals by PAI technique. Up to20%Tb, the LY is in the order of 24,000 ph MeV−1, i.e. ∼70%brighter than standard CWO. The measured PL decay time ofthe green luminescence is close to 1ms, which is in goodagreement with the theoretical estimation by JO analysis. Byfurther comparison with the XRL decay, an LY improvement of∼36%, reaching 33,000 ph MeV−1, is expected upon elimi-nating or neutralizing non-radiative recombination centers. Thisresult proves the potential of Tb:YTO single crystals to substituteCWO in high-energy X-ray imaging applications.Acknowledgments The authors would like to express their sincere thanksto Dr. Yuichi Oshima for his kind help with the refractive index measurementsand to Mr. Satoshi Yamamoto for his support with the polishing of variouscrystals.1) T. Yanagida, “Inorganic scintillating materials and scintillation detectors,”Proc. Jpn. Acad. Ser. B 94, 5 (2018).2) W. W. Moses, “Scintillator requirements for medical imaging,”SCINT99LBNL-45805.3) X. Yan, G. R. Fern, R. Withnall, and J. Silver, “Effects of the host latticeand doping concentration on the colour of Tb3+ cation emission in ofY2O2S:Tb3+ and Gd2O2S:Tb3+ nanometer sized phosphor particles,”Nanoscale 5, 8640 (2013).4) I. Kandarakis and D. Cavouras, “Experimental and theoretical assessment of theperformance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb-La2O2S:Tb mixtures for X-ray imaging,” Eur. Radiol. 11, 1083 (2001).5) S. 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Eng. 57, 017107 (2018).Table III. Comparison of JO parameters Ωt (t = 2, 4, and 6) (×10−20 cm2), and radiative τR and PL τPL lifetimes of Tb3+ in various crystals (* glass).Crystal Ω2 Ω4 Ω6 τR (ms) τPL (ms) References15%Tb:YTO 6.6 3.5 3.08 1.14 0.976 this work55%Tb:YTO 5.7 3.6 3.07 1.23 0.286 “TTO 5.6 2.8 2.76 1.3 0.257 “3%Tb:30Li2O·70B2O3 * 5.56 1.33 3.22 — —26)5%Tb:CaF2 1.71 2.65 2.25 6.77 6.06 33)LiTbF4 1.5 2.23 2.06 6.8 3.8 34)Tb0.81Ca0.19F2.81 1.14 1.52 1.82 6.9 4.2 34)TbP5O14 3.77 1.7 3.43 3.82 3.4 35)TbLiP4O12 3.5 2.43 1.8 4.09 3.7 35)Ba3Tb(PO4)3 2.53 8.55 1.3 3.54 3.17 36)TbAl3(BO3)4 8.15 0.29 2.44 2.07 0.8 35)7%Tb:Na3La9O3(BO3)8 1.05 11.74 1.59 2.38 2.02 37)1%Tb:KYb(WO4)2 0.86 1.66 1.98 2.08 0.395 38)0.1%Tb:YAlO3 3.25 7.13 2 2.07 1.71 39)7%Tb:Y3Al5O12 2.75 0.12 3.37 3.3 3.12 40)Tb:YAlO3 3.49 5.87 2.55 2.31 1.72 41)TbAlO3 40.52 8.74 2.26 3.5 2 42)Tb:Lu2O3 3.79 1.3 1.08 3.02 1.13 43)Tb3Sc2Al3O12 4.47 1.37 4.23 — —44)Supplementary table. 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