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## Creator

[Akihiro Nakanishi](https://orcid.org/0009-0001-1859-261X), [Shiro Funahashi](https://orcid.org/0000-0002-9381-3603), [Yukinori Koyama](https://orcid.org/0000-0002-7090-4430), Hisanori Yamane, [Kohsei Takahashi](https://orcid.org/0000-0002-6443-1534), [Takayuki Nakanishi](https://orcid.org/0000-0003-3412-2842), [Naoto Hirosaki](https://orcid.org/0000-0001-9218-9557), [Takashi Takeda](https://orcid.org/0000-0003-2510-4562)

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[Blue–Green Emitting Phosphor Ba                    <sub>2</sub>                    LiAlSi                    <sub>2</sub>                    O                    <sub>8</sub>                    :Eu                    <sup>                      2                      +                    </sup>                    for Phosphor-Converted Light-Emitting Diodes via Single-Particle Diagnosis in a Quasi-Quaternary System](https://mdr.nims.go.jp/datasets/13cfb621-da45-4688-81b0-1477b8b4bc71)

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Blue–Green Emitting Phosphor Ba2LiAlSi2O8:Eu2+ for Phosphor-Converted Light-Emitting Diodes via Single-Particle Diagnosis in a Quasi-Quaternary SystemBlue−Green Emitting Phosphor Ba2LiAlSi2O8:Eu2+ for Phosphor-Converted Light-Emitting Diodes via Single-Particle Diagnosis in aQuasi-Quaternary SystemAkihiro Nakanishi, Shiro Funahashi, Yukinori Koyama, Hisanori Yamane, Kohsei Takahashi,Takayuki Nakanishi, Naoto Hirosaki, and Takashi Takeda*Cite This: ACS Appl. Mater. Interfaces 2026, 18, 28857−28865 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: Phosphor-converted light-emitting diodes (PC-LEDs) are widely usedin various fields due to their long lifetime and high energy efficiency. In particular,blue−green-emitting phosphors have the potential to fill the cyan gap in white LEDsand to be used in display indicators for autonomous driving. A new blue−green-emitting Ba2LiAlSi2O8:Eu2+ phosphor was discovered through exploratory experi-ments in the BaO−Li2O−Al2O3−SiO2 quasi-quaternary system using a single-particle-diagnosis approach. Single-crystal X-ray diffraction analysis revealed thatBa1.96Eu0.04LiAlSi2O8 crystallizes in a space group of Pna21 (No. 33) with a =8.04521(11) Å, b = 19.0484(2) Å, c = 5.02228(6) Å, and Z = 4. The crystal structurecomprises LiO4, AlO4, and SiO4 tetrahedra, which orderly align and form aframework by sharing apical oxygen atoms. Ba atoms are surrounded by eight andseven oxygen atoms in the framework. Density functional theory calculationscorroborated the Al and Si arrangement in the Ba2LiAlSi2O8 crystal structure. Asingle-phase powder of the Ba2LiAlSi2O8:Eu2+ phosphor was successfully obtained via a solid-state reaction. This phosphor exhibiteda blue−green luminescence peak at 497 nm with a full width at half-maximum of 85 nm under 372 nm excitation. The internal andexternal quantum efficiencies were 51.0% and 42.7%, respectively. The peak intensity at 150 °C was 67% of that at roomtemperature. We fabricated pc-LEDs based on 405 nm LED chips combined with Ba2LiAlSi2O8:Eu2+ phosphor, and the CIEchromaticity coordinates were in the blue−green region. These results indicate that the new Ba2LiAlSi2O8:Eu2+ phosphor is apromising candidate for future LED technologies.KEYWORDS: Eu2+-activated phosphor, single-crystal X-ray diffraction, quasi-quaternary system, new crystal phase,phosphor-converted LEDs1. INTRODUCTIONPhosphor-converted light-emitting diodes (pc-LEDs) haveapplications in various fields due to their advantages of longlife and high-energy efficiency.1−3 A typical example is thecombination of blue-LEDs4 and yellow phosphors to createwhite light.5 Color-conversion phosphors are widely studiedfor various applications. Particularly, yellow-emitting( Y 3 A l 5 O 1 2 : C e 3 + a n d C a - α - S i A l O N(Cam/2Si12−m−nAlm+nOnN16−n:Eu2+)), blue-emitting (BaMgA-l10O17:Eu2+), and red-emitting (CaAlSiN3:Eu2+ andM2Si5N8:Eu2+ (M = Ca, Sr)) phosphors are commerciallyavailable for fabricating white LEDs comprising blue orultraviolet LED chips.5−9 Narrow-band green phosphor β-SiAlON:Eu2+ (Si6−zAlzOzN8−z:Eu2+) is used in liquid crystaldisplay backlights to enlarge color gamuts.10,11The development of blue−green emitting phosphors, whichare used for developing high color-rendering white LEDs to fillcyan gaps, has attracted considerable attention in theadvancement of LED applications.12,13 In addition, blue−green lights with wavelengths of 440−570 nm exhibit deeppenetration depth in marine environments, resulting in theirusage for underwater wireless optical communication, fishattractions, and aquaculture in marine ranching systems.14,15Recently, turquoise-colored exterior marker lights have beenapproved by Mercedes-Benz for vehicles equipped with itsDrive Pilot SAE (Society of Automotive Engineers) Level 3automated driving system.16 Therefore, blue−green emittingphosphors are expected to play a pivotal role in future LEDtechnologies.Eu2+- or Ce3+-activated phosphors are attractive for LEDapplications because of the parity-allowed transition betweenReceived: February 2, 2026Revised: April 30, 2026Accepted: May 6, 2026Published: May 14, 2026Research Articlewww.acsami.org© 2026 The Authors. Published byAmerican Chemical Society28857https://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−28865This article is licensed under CC-BY 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on June 1, 2026 at 10:24:19 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Akihiro+Nakanishi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shiro+Funahashi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yukinori+Koyama"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hisanori+Yamane"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kohsei+Takahashi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takayuki+Nakanishi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takayuki+Nakanishi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Naoto+Hirosaki"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Takeda"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acsami.6c02416&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=agr1&ref=pdfhttps://pubs.acs.org/toc/aamick/18/20?ref=pdfhttps://pubs.acs.org/toc/aamick/18/20?ref=pdfhttps://pubs.acs.org/toc/aamick/18/20?ref=pdfhttps://pubs.acs.org/toc/aamick/18/20?ref=pdfwww.acsami.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://www.acsami.org?ref=pdfhttps://www.acsami.org?ref=pdfhttps://creativecommons.org/licenses/by/4.0/5d- and 4f-orbital.17 Their luminescence properties arestrongly influenced by the local structure surrounding Eu2+or Ce3+,18−21 and this local structure varies with the hostmaterial. Therefore, the discovery of suitable host materials iscrucial for accelerating phosphor development. However,identifying new host materials remains time-consuming andcostly because no clear guidelines for their discovery have beenestablished so far. Traditionally, phosphor development hasrelied on a trial-and-error approach, typically using known hostmaterials listed in databases (e.g., Inorganic Crystal StructureDatabase22) or by exhaustively screening possible elementalcombinations to find new host materials. We previouslyproposed a single-particle-diagnosis approach that is highlyeffective for discovering new phosphors.23 This approachenables the direct determination of the crystal structure andluminescence properties of single-crystal phosphors frommultiphase powders containing various secondary phases,without the need for single-phase synthesis. Using thisapproach, new (oxy)nitr ide phosphors , such asBa5Si11Al7N25:Eu2+, BaSi4Al3N9:Eu2+, Ba2LiSi7AlN12:Eu2+,Sr3Si8−xAlxO7+xN8−x :Eu2+, Ca1.62Eu0.38Si5O3N6, andSi2.5Al9.5O0.5N12.5:Eu2+, were discovered.23−27Oxide materials are relatively easy to synthesize; con-sequently, numerous oxide-based compounds have beenreported. To further expand the exploration of oxide materials,exploratory experiments in multicomponent systems combin-ing the single-particle-diagnosis approach offer a more effectivestrategy for material discovery. In this study, we explored a newoxide-based Eu2+-activated phosphor in the BaO−Li2O−Al2O3−SiO2 quasi-quaternary system. In previous studies,Eu2+ -activated phosphors have been discovered in the Ba−Li−Al−Si−N system using the single-particle-diagnosis ap-proach.24 Eu2+ -doped Ba2SiO4, BaAl2Si2O8, BaSiO3,Li2BaSiO4, and BaAl2O4 have been reported to exhibit blueto yellow emission.28−32 However, in the oxide-based Ba−Li−Al−Si−O system, no new phases have yet been discovered,leaving room for further exploration. A new blue−greenemitting Ba2LiAlSi2O8:Eu2+ phosphor was discovered using thesingle-particle-diagnosis approach, and a Ba2LiAlSi2O8:Eu2+phosphor powder was successfully synthesized for pc-LEDapplication.2. EXPERIMENTAL SECTION2.1. Exploratory Synthesis and Characterization ofParticlesVarious Ba/Eu/Li/Al/Si/O compositions were explored withreagents of BaCO3 (99.95%, Kojundo Chemical, Japan), Li2CO3(99.99%, Kojundo Chemical, Japan), Al2O3 (99.99%, TAIMEICHEMICALS Co., LTD, Japan), SiO2 (99.9%, Kojundo Chemical,Japan), and Eu2O3 (99.9%, Shin-Etsu Chemical Co., LTD, Japan).The mixed precursor powders were calcined on an alumina boat at1050 °C for 5 h in a reducing atmosphere (H2:N2 = 5:95 gas). Theresulting powders were excited by a 365 nm LED, and a blue−greenemitting phosphor particle was collected under microscopeobservation. Single-crystal X-ray diffraction (XRD) measurements ofthe particles were performed using a diffractometer (XtaLab Synergy-Custom, Rigaku, Japan) with Mo−Kα radiation (λ = 0.71073 Å).Data were integrated and corrected for absorption using CrysAlisPro.The crystal structures were refined by SHELX.33,34 The chemicalcompositions were analyzed using a scanning electron microscope(Hitachi High-Technology, SU1510) with an energy dispersivespectroscope (EDS, Bruker AXS, XFlash SDD) operated at 10 kV.The excitation and emission spectra of the particles were measuredusing a self-made device and analyzed using a proximity method.352.2. Density Functional Theory Calculations to ExamineCation Ordering in Ba2LiAlSi2O8Density functional theory (DFT) calculations were performed usingthe plane-wave basis projector augmented wave method, asimplemented in the Vienna Ab initio simulation package VASP6.3.2,36,37 to examine the arrangement of Li, Al, and Si atoms inBa2LiAlSi2O8. The Perdew−Burke−Ernzerhof exchange-correlationfunctional38 was used, with the cutoff energy set to 520 eV.Reciprocal-space integration was conducted using a gamma-centered2 × 2 × 4 mesh. The total energy converged to 10−9 eV/atom. Thelattice constants and internal coordinates were optimized until theforce converged to 0.01 eV/Å.2.3. Powder Synthesis and Characterization ofBa2LiAlSi2O8:Eu2+Ba2(1−x)Eu2xLiAlSi2O8 (x = 0, 0.005, 0.02, 0.04, and 0.06) phosphorswere synthesized via a solid-state reaction. The stoichiometricamounts of BaCO3, Li2CO3, Al2O3, SiO2, and Eu2O3 were thoroughlymixed in an alumina mortar. After mixing, the precursor powder wascalcined in the alumina boat at 1050 °C for 5 h in a reducingatmosphere (H2:N2 = 5:95 gas). The crystal phases of the phosphorswere analyzed at room temperature via powder XRD (SmartLab X-rayDiffractometer, Rigaku, Japan) with Cu-Kα1 radiation at 45 kV, 200mA, and 2θ in the range of 10°−90°. The XRD data were analyzedusing Rigaku PDXL 2 software. The luminescence properties ofpowder samples were measured with a fluorescence spectrometer(FP-8600 Spectrofluorometer, JASCO, Japan), and the decay curveswere measured with a fluorescence spectrometer (FLS1000Spectrofluorometer, Edinburgh Instruments Ltd., UK) under theexcitation of a 375 nm pulse laser diode. The internal quantumefficiency (IQE) and external quantum efficiency (EQE) of thephosphors were measured using a QE-2100 system (OtsukaElectronics, Japan). BaSO4 was used for a white reference. Thecation content was analyzed via inductively coupled plasma opticalemission spectroscopy (5800 ICP-OES, Agilent, USA). The measure-ment solution was prepared by dissolving the sample powder insolution. Sample powder was fused with sodium carbonate and boricacid in a platinum crucible. After cooling, the melt was dissolved in 10mL of HCl (1 + 1) and diluted with water. The solution wastransferred to a flask, and Yb standard solution was added as aninternal standard. The temperature-dependent luminescence proper-ties were measured using the QE-2100 system combined with atemperature control stage (10002L, Linkam Scientific Instruments,UK).2.4. Characterization of pc-LED with Ba2LiAlSi2O8: Eu2+PhosphorThe pc-LEDs were fabricated by coating a mixture of the obtainedphosphors and silicone resin and with a 405 nm LED chip.Particularly, the obtained phosphors and silicone resin were mixedat a weight ratio of 1:3. The resulting paste mixture was coated on theLED chip and heated at 150 °C for 30 min to cure the resin. Theelectroluminescence (EL) spectra of the obtained pc-LEDs weremeasured using the QE-2100 system.3. RESULTS AND DISCUSSION3.1. New Phosphor DiscoveryA new oxide phosphor was discovered in the product from acomposition of Ba/Eu/Li/Al/Si = 39.2:0.8:10:10:40. Figure 1shows a microscopic photograph of the powder product under365 nm excitation light. Several particles showed emission inthe blue−green region, and some particles with yellowemission were observed. Ba2SiO4, BaSiO3, and BaAl2Si2O8were identified in the powder XRD analysis (Figure S1). Ithas been reported that Ba2SiO4: Eu2+ and BaAl2Si2O8: Eu2+phosphors show blue emission28,29 and BaSiO3: Eu2+ showsyellow emission.30 However, some XRD peaks were notconsistent with known Ba/Li/Al/Si-containing oxides, suggest-ACS Applied Materials & Interfaces www.acsami.org Research Articlehttps://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−2886528858https://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfwww.acsami.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asing it is a new compound. In the single-crystal XRD analysis ofthe emission particles, a new phosphor with blue−greenemission was discovered. Figure S2 shows the excitation andemission spectra of blue−green emitting single particles. Themonitored excitation spectrum has a broad band in the near-ultraviolet (UV) region, and the emission spectrum shows anemission peak at 491 nm under 350 nm irradiation.The blue−green emitting particle was determined as a newBa2LiAlSi2O8 material via the single-crystal XRD analysis.Table 1 lists the crystallographic data and refinement structureparameters. Table 2 lists the fractional coordinates. The Euoccupancy was refined based on the nominal Eu content of 2%relative to Ba, as defined by the starting stoichiometric ratioused in the synthesis. The crystal structure has anorthorhombic system with a = 8.04521(11) Å, b =19.0484(2) Å, c = 5.02228(6) Å, and a space group of Pna21(No. 33). The reliability factors R1 and wR2 were 2.41% and3.71%, respectively. Table S1 lists the anisotropic displacementparameters. Figure S3 shows the EDS spectrum and analyzedcation ratio of the blue−green emitting single particles. Noclear Eu signal was obtained because the amount of Eu issmall; thus, it was excluded from the analysis. The atomicratios of Ba, Al, and Si were 13.6%, 7.2%, and 13.9%,respectively. The cation ratio is in close agreement with the2:1:2 ratio obtained by single-crystal XRD structural analysis.Figure 2 shows the crystal structure of Ba2LiAlSi2O8, drawnusing VESTA.39 The Wyckoff position is only a general 4a sitein the space group of Pna21. The crystal structure comprisescorner-sharing tetrahedra of LiO4, AlO4, and SiO4, which areorderly arranged in the framework, and the tetrahedra alignalong the c axis. SiO4 tetrahedra are isolated with other SiO4tetrahedra in the structure, indicating it is a member of thenesosilicate group. Al and Si often occupied the samecrystallographic sites in aluminosilicates; however, Al and Sioccupied different crystallographic sites in Ba2LiAlSi2O8.To investigate in detail the distribution of Al and Si, whichhave similar X-ray atomic scattering factors, the cationarrangement at the tetrahedral sites was additionally examinedusing DFT calculations. Twelve structure models wereconstructed by placing Li, Al, and Si ions at four tetrahedralsites (T1, T2, T3, and T4). The lattice constants and internalcoordinates were optimized via DFT calculations to minimizetotal energy. Table 3 shows the cation arrangements andrelative DFT energies of the four lowest-energy structuremodels, as well as the R1 and wR2 values obtained from theXRD structural analysis. Other cation arrangements wereexcluded because they had higher relative DFT energies. Thelowest-energy arrangement (Li, Al, Si, Si) was identical to thearrangement obtained from the XRD analysis. The arrange-ment with Li and Al swapped (Al, Li, Si, Si) had the second-lowest energy. However, its energy was 0.997 eV/formula-unithigher than that of the lowest-energy structure. Theconfiguration entropy of a completely random arrangementis −4 kB (0.25 log 0.25 + 0.25 log 0.25 + 0.5 log 0.5) = 0.156meV/K formula-unit, where kB denotes the Boltzmannconstant. This corresponds to an energy of 0.206 eV at 1050°C. The difference between the lowest and second-lowestenergies was significantly larger than the configuration entropy.Therefore, the cations were ordered at the tetrahedral sites,and the degree of disordering should be small. An XRDanalysis was also attempted for this cation arrangement, andthe R1 and wR2 values were unacceptably large. Thearrangement with the third-lowest energy was (Li, Si, Si, Al),and the arrangement with the fourth-lowest one was (Li, Si, Al,Si), which had swapped Al and Si compared with thearrangement with the lowest energy. Because Al and Si aredifficult to distinguish in an XRD analysis, the R1 and wR2values obtained for these two arrangements were comparableto those of the lowest-energy structure. However, DFTcalculations showed higher energies of 1.203 and 1.253 eV/formula-unit for these structures, respectively. Thus, the DFTFigure 1. Photograph of a powder product from the composition ofBa/Eu/Li/Al/Si = 39.2:0.8:10:10:40 under 365 nm excitation light.The inset shows the selected blue−green luminescent particle foranalysis.Table 1. Crystallographic Data and Structure RefinementParameters of Ba1.96Eu0.04LiAlSi2O8aFormula Ba1.96Eu0.04LiAlSi2O8Formula mass (g mol−1) 493.36Crystal system OrthorhombicSpace group Pna21 (No. 33)Temperature (K) 293a (Å) 8.04521(11)b (Å) 19.0484(2)c (Å) 5.02228(6)V (Å3) 769.659(17)Z 4Radiation type Mo Kαμ (mm−1) 10.727θ range for data collection (°) 2.7380 to 38.5940Index ranges −13 ≤ h ≤ 10, −31 ≤ k ≤ 31,−8 ≤ l ≤ 8Crystal size (mm) 0.019 × 0.017 × 0.011Diffractometer ROD, Synergy Custom system, HyPix-Arc150Absorption correction MultiscanTmin, Tmax 0.827, 1.000Reflection collected 55852Independent reflections 3736Final R indexes [I ≥ 2σ (I)] R1 = 0.0218, wR2 = 0.0367Final R indexes [all data] R1 = 0.0241, wR2 = 0.0371S 1.204Δρmax, Δρmin (e Å−3) 1.07, −1.40aR1, wR2 are reliability factors. S is goodness of fit. R1=∑|(|Fo| − |Fc|)|/∑ | F o | . = { [ ] [ ]}wR w F F w F( ) / ( )o c o22 2 2 2 2 1/2.= { [ ] }S w F F n p(( ) ) /( )o c2 2 2 1/2.= [ + + ]w F P P1/ ( ) (0.009 ) 1.6987o2 2 2 .= [ + ]P F F2 max( , 0) /3c o2 2 . Fo is the observed structure factor, Fc isthe calculated structure factor, σ is the standard deviation of Fo2, n isthe number of reflections, and p is the number of refined parameters.ACS Applied Materials & Interfaces www.acsami.org Research Articlehttps://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−2886528859https://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig1&ref=pdfwww.acsami.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ascalculation results were consistent with the ordered cationarrangement obtained via XRD analysis.Considering the tetrahedral framework of Ba2LiAlSi2O8,each LiO4 tetrahedron shares corners with two LiO4 units, oneAlO4 unit, and four SiO4 units, whereas each AlO4 tetrahedronshares corners with one LiO4 unit and four SiO4 units. Fromthe electrostatic repulsion viewpoint, the LiO4 tetrahedronshares corners with a greater number of surrounding tetrahedrathan the AlO4 tetrahedron due to the lower valence state ofLi+. Ba occupies two polyhedral sites formed by the tetrahedralframework, where the Ba1 and Ba2 sites are coordinated byeight and seven oxygen atoms, respectively. Table S2summarizes the cation−anion distances and bond valencesums (BVS).40 The average Ba−O distances for the Ba1 andBa2 sites are 2.87 and 2.79 Å, respectively. The BVS values forBa1 and Ba2 are 1.88 and 1.91, respectively. The average bondlengths of Li−O, Al−O, Si1−O, and Si2−O are 2.00, 1.75,1.63, and 1.63 Å, respectively. These values correspond to theorder of the ionic radii of Li+ (0.59 Å), Al3+ (0.39 Å), and Si4+(0.26 Å). The BVS values for the Li, Al, Si1, and Si2 sites are0.95, 3.07, 3.99, and 3.91, respectively. From the BVS values, itis clearly confirmed that Li+, Al3+, and Si4+ are orderly arrangedat the tetrahedral sites.The crystal structure of Ba2LiAlSi2O8 is related to those ofPbZnSiO4 (larsenite) and PbLiPO4.41,42 Considering thecrystal structure of Ba2LiAlSi2O8 based on that of PbZnSiO4,the Pb site is substituted by Ba and the Zn site is orderlysubstituted by Li and Al in a 1:1 ratio. Based on that ofPbLiPO4, the Pb site is substituted by Ba and half of the Li siteis orderly substituted by Al. The PO4 unit is substituted by theSiO4 unit. Figure 3 shows the phase diagram of the BaO-Li2O−Al2O3−SiO2 quasi-quaternary system. Li7Ba3Al3O11,LiBa2AlO4 (Li−Ba−Al−O system), Li2BaSiO4 (Li−Ba−Si−Osystem), Ba13Al22Si10O66, BaAl2Si2O8 (Ba−Al−Si−O system),LiAlSiO4, LiAlSi2O6, and LiAlSi4O10 (Li−Al−Si−O system)are known crystal phases of the quasi-ternary system.43−50 Insummary, single-crystal XRD analysis and DFT calculationsrevealed that a new crystal phase, Ba2LiAlSi2O8, was identifiedin the BaO-Li2O−Al2O3−SiO2 quasi-quaternary system.Table 2. Occupancies, Fractional Atomic Coordinates, and Equivalent Isotropic Atomic Displacement Parameters (Ueq) ofBa1.96Eu0.04LiAlSi2O8aAtom Occupancy x y z Ueq (Å2)Ba/Eu1 0.979(3)/0.021(3) 0.18003(3) 0.55048(2) 0.37803(5) 0.00919(4)Ba/Eu2 0.981(3)/0.019(3) 0.47812(2) 0.72172(2) 0.40001(5) 0.00916(4)Li 1 0.4870(8) 0.5581(4) 0.8649(18) 0.0119(12)Al 1 0.80188(13) 0.65697(5) 0.8667(3) 0.00543(18)Si1 1 0.19239(11) 0.68060(4) 0.8825(3) 0.00532(13)Si2 1 0.71634(12) 0.57203(5) 0.3649(2) 0.00545(16)O1 1 0.8616(4) 0.51509(14) 0.3463(6) 0.0122(6)O2 1 0.6950(4) 0.59328(14) 0.6833(5) 0.0075(5)O3 1 0.7679(4) 0.64613(15) 0.2089(5) 0.0098(5)O4 1 0.2222(4) 0.76149(14) 0.7714(6) 0.0094(5)O5 1 0.5406(4) 0.54571(16) 0.2467(6) 0.0110(5)O6 1 0.3354(4) 0.63184(15) 0.7611(6) 0.0103(5)O7 1 0.1888(4) 0.68277(15) 0.2021(5) 0.0096(5)O8 1 0.0094(4) 0.65832(16) 0.7660(6) 0.0103(5)aUeq = (1/3){U11(aa*)2 + U22(bb*)2 + U33(cc*)2 + 2U12a* b* ab cos γ + 2U13a* c* ac cos β + 2U23b* c* bc cos α}.Figure 2. Crystal structure viewed from (a) the c axis and (b) the aaxis, and polyhedra of (c) Ba/Eu1- and Ba/Eu2-site ofBa1.96Eu0.04LiAlSi2O8. Black solid line represents the unit cell. Cyanand light cyan spheres are Ba/Eu1 and Ba/Eu2 sites. Red, green, andblue tetrahedra are LiO4, AlO4, and SiO4. Light gray spheres representO atoms.Table 3. Cation Arrangement at Tetrahedral Sites, RelativeEnergies Evaluated by DFT Calculations, and XRD AnalysisResults for the Four Lowest-Energy Cation ArrangementsNo. T1 T2 T3 T4 ΔE (eV/formula-unit) R1 (%) wR2 (%)1 Li Al Si Si 0 2.41 3.712 Al Li Si Si 0.997 9.44 23.813 Li Si Si Al 1.203 2.46 3.964 Li Si Al Si 1.253 2.47 4.01Figure 3. Phase diagram of the BaO−Li2O−Al2O3−SiO2 quasi-quaternary system.ACS Applied Materials & Interfaces www.acsami.org Research Articlehttps://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−2886528860https://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig3&ref=pdfwww.acsami.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as3.2. Powder Synthesis and Luminescence Properties ofBa2LiAlSi2O8: Eu2+ PhosphorsTo evaluate the luminescence properties of powder phosphorsand fabricate the prototype of pc-LEDs, powder synthesis wasperformed based on the Ba2LiAlSi2O8:Eu2+ composition.F igure 4 shows the powder XRD pat te rns o fBa2(1−x)Eu2xLiAlSi2O8 (x = 0, 0.005, 0.02, 0.04, and 0.06).The XRD patterns of all samples are consistent with thediffraction patterns calculated from the crystal structuredetermined by single-crystal XRD analysis. The crystal phaseof Ba2LiAlSi2O8 was mainly obtained in all samples. Figure 5shows the lattice parameters of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0,0.005, 0.02, 0.04, and 0.06) phosphors obtained by wholepattern fitting. The linear decrease in the lattice parameterswith an increase in Eu content is attributed to the difference inthe ionic radii between Ba2+ (rVIII = 1.42 Å) and Eu2+ (rVIII =1.25 Å),51 which produces the lattice distortion.52 Table 4summarizes the cation contents obtained by ICP analysis. Theexperimental result (Ba:Eu:Li:Al:Si = 1.91:0.08:1.00:1.00:2.00)corresponds to the theoretical atomic ratio value ofBa2(1−x)Eu2xLiAlSi2O8 (x = 0.04).Figure 6 shows the excitation and emission spectra ofBa2(1−x)Eu2xLiAlSi2O8 (x = 0.005, 0.02, 0.04, and 0.06)phosphors. The Eu concentration optimized to show thehighest intensity was given by x = 0.04. In the x = 0.04 sample,the broadband excitation spectrum is shown from 200 to 450nm while the emission spectrum shows a peak at 497 nm witha full width at half-maximum of 85 nm under 372 nmexcitation, which originated from the 5d−4f transition of Eu2+in the Ba2LiAlSi2O8 host material. With an increase in Eucontent, the excitation band intensity at wavelengths longerthan 400 nm increased and the emission peak position slightlyshifted to longer wavelengths. The excitation and emissionintensities gradually increased with Eu content and finallydecreased in the sample with x = 0.06 due to the concentrationquenching. No significant change in the emission peak wasobserved for this phosphor even after prolonged UV excitationfor 5 h.53 The IQE and EQE of the Ba2(1−x)Eu2xLiAlSi2O8 (x =0.04) phosphor obtained by 372 nm excitation were 51.0% and42.7%, respectively.Figure 7 shows the luminescence decay curve of theBa2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor. The lifetime wasobtained by fitting the decay curve with a biexponentialfunction corresponding to two Eu2+ sites in the crystalFigure 4. XRD patterns of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0, 0.005, 0.02,0.04, and 0.06) phosphors.Figure 5. Lattice constant of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0, 0.005,0.02, 0.04, and 0.06) phosphors.Table 4. Cation Composition of Ba2(1−x)Eu2xLiAlSi2O8 (X = 0.04) Phosphors by ICP AnalysisaBa Eu Li Al Si O TotalTheoretical (wt %) 53.4 2.46 1.41 5.46 11.4 25.87 100.0ICP result (wt %) 52.7 2.43 1.40 5.43 11.3 25.71b 98.9Mol ratio of ICP result (fixed Al to 1 mol) 1.91 0.08 1.00 1 2.00aThe molar ratio of cation is also listed. bThis value was calculated from the metal element contents.Figure 6. Excitation (λem = 497 nm) and emission (λex = 372 nm)spectra of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0.005, 0.02, 0.04, and 0.06)phosphors.ACS Applied Materials & Interfaces www.acsami.org Research Articlehttps://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−2886528861https://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig5&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig6&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig6&ref=pdfwww.acsami.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asstructure and a background term. The decay components weredetermined to be 0.19 and 0.58 μs, with relative weights of1247 and 8691, respectively. The average decay time wascalculated to be 0.56 μs, which is consistent with typical valuesfor the 5d−4f transitions of Eu2+.Figure 8a and b shows the temperature-dependentl um i n e s c e n c e s p e c t r a a n d i n t e n s i t y o f t h eBa2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor. Figure S4 showstemperature-dependent normalized luminescence spectra. Thephotoluminescence intensity gradually decreased with increas-ing temperature from 25 to 300 °C due to the thermalquenching effect. At 150 °C, the peak and integrated intensitieswere 67% and 70% of those at room temperature, respectively.There is little difference between changes in peak andintegrated intensities, indicating that the peak shape changesslightly. No additional peaks or noticeable peak shifts wereobserved. These results are favorable for LED applications withno chromatic shift.3.3. Electroluminescence of Blue−Green Emitting pc-LEDswith Ba2LiAlSi2O8:Eu2+ PhosphorTo investigate the potential of the Ba2(1−x)Eu2xLiAlSi2O8 (x =0.04) phosphor, a pc-LED with 405 nm LED chip wasfabricated. Figure 9 shows the EL spectrum of the blue−greenemitting LED with 405 nm LED chip under forward-biascurrents from 10 to 60 mA. The inset shows the pc-LEDemission when the current is turned on. The EL spectra showthe emission band at around 400 nm derived from the LEDchip and the blue−green emission band of Ba2LiAlSi2O8: Eu2+phosphor at around 500 nm. The CIE chromaticitycoordinates of the LED are shown in Figure 10. With anincrease in current, the CIE chromaticity coordinates wereslightly shifted in the blue−green region. The blue−greenphosphor developed in this study has the potential to fill thecyan gap in white LEDs. In addition, the color coordinated foran automated driving system (ADS) marker lamp is regulatedin the blue−green region of (CIE x, CIE y) = (0.012, 0.495),(0.200, 0.400), (0.200, 0.320), and (0.040, 0.320) by the SAE.Finally, we emphasized that the novel blue−greenBa2LiAlSi2O8: Eu2+ phosphor has potential for exterior ADSmarker lights and future pc-LED applications.4. CONCLUSIONA new oxide-based blue−green emitting Ba2LiAlSi2O8:Eu2+phosphor was discovered using a single-particle-diagnosisapproach. The crystal structure, which is related to those ofFigure 7. Measured (light-blue dot) and fitted (black line) decaycurves of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor.Figure 8. (a) Temperature-dependent luminescence spectra, (b) peak and integrated intensities of Ba2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphorunder 372 nm excitation.Figure 9. EL spectra of blue−green emitting LEDs with 405 nm LEDchips and Ba2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor. The insetshows the pc-LED emission observed when the current is turned on.ACS Applied Materials & Interfaces www.acsami.org Research Articlehttps://doi.org/10.1021/acsami.6c02416ACS Appl. Mater. Interfaces 2026, 18, 28857−2886528862https://pubs.acs.org/doi/suppl/10.1021/acsami.6c02416/suppl_file/am6c02416_si_002.pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig7&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig8&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig8&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig8&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig8&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig9&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig9&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig9&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsami.6c02416?fig=fig9&ref=pdfwww.acsami.org?ref=pdfhttps://doi.org/10.1021/acsami.6c02416?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asPbZnSiO4 (larsenite) and PbLiPO4, was revealed via single-crystal XRD analysis. DFT calculations corroborated the Aland Si arrangement obtained from the single-crystal XRDanalysis results. Powder phosphor of Ba2LiAlSi2O8:Eu2+ wassuccessful ly obtained via a sol id-state react ion.Ba2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor showed a blue−green emission under 372 nm excitation. The IQE and EQEwere 51.0% and 42.7%, respectively. The peak intensity at 150°C was 67% of that at room temperature. The EL spectra ofthe corresponding pc-LEDs showed a blue−green emissionband, and the CIE chromaticity coordinates were in the blue−green region regulated by the SAE, indicating that the blue−green emitting Ba2LiAlSi2O8:Eu2+ phosphor has potentialapplications in exterior ADS marker lights and future LEDtechnologies. The single-particle-diagnosis approach is effectivefor discovering new phosphors; thus, it will facilitate thedevelopment of pc-LEDs.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acsami.6c02416.CIF file (Ba1.96Eu0.04LiAlSi2O8) (CIF)Figure S1: XRD pattern of the powder product of Ba/Eu/Li/Al/Si = 39.2:0.8:10:10:40 calcined at 1050°C for5 h in a reducing atmosphere (H2:N2 = 5:95 gas); FigureS2: excitation and emission spectra of the blue−greenemitting single particle; Figure S3: EDS spectrum of theblue−green emitting single particle; Figure S4: temper-ature-dependent normalized luminescence spectra ofBa2(1−x)Eu2xLiAlSi2O8 (x = 0.04) phosphor under 372nm excitation; Table S1: anisotropic displacementparameters (Å2) of Ba1.96Eu0.04LiAlSi2O8; Table S2:bond length, average bond length (Å) and BVS forBa1.96Eu0.04LiAlSiO8 (PDF)■ AUTHOR INFORMATIONCorresponding AuthorTakashi Takeda − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,Japan; orcid.org/0000-0003-2510-4562;Email: TAKEDA.Takashi@nims.go.jpAuthorsAkihiro Nakanishi − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,Japan; orcid.org/0009-0001-1859-261XShiro Funahashi − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,JapanYukinori Koyama − Center for Basic Research on Materials,National Institute for Materials Science, Tsukuba, Ibaraki305-0047, Japan; orcid.org/0000-0002-7090-4430Hisanori Yamane − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,JapanKohsei Takahashi − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,JapanTakayuki Nakanishi − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,Japan; orcid.org/0000-0003-3412-2842Naoto Hirosaki − Advanced Phosphor Group, NationalInstitute for Materials Science, Tsukuba, Ibaraki 305-0044,JapanComplete contact information is available at:https://pubs.acs.org/10.1021/acsami.6c02416Author ContributionsThis manuscript was written through the contributions of allauthors. All authors have approved the final version of themanuscript.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSThis work was supported by JST, the Core Research forEvolution Science and Technology (grant numberJPMJCR19J2). A part of the calculations in this study wasperformed on the Numerical Materials Simulator at theNational Institute for Materials Science.■ REFERENCES(1) Schubert, E. F.; Kim, J. K. Solid-State Light Sources GettingSmart. Science 2005, 308, 1274−1278.(2) Humphreys, C. J. Solid-State Lighting. MRS Bull. 2008, 33,459−470.(3) Lin, C. C.; Liu, R.-S. Advances in Phosphors for Light-EmittingDiodes. J. Phys. Chem. Lett. 2011, 2, 1268−1277.(4) Nakamura, S.; Mukai, T.; Senoh, M. Candela-Class High-Brightness InGaN/AlGaN Double-Heterostructure Blue-Light-Emit-ting Diodes. Appl. Phys. Lett. 1994, 64, 1687−1689.(5) Xia, Z.; Meijerink, A. Ce3+ -Doped Garnet Phosphors:Composition Modification, Luminescence Properties and Applica-tions. Chem. Soc. 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