基于%5BLnMo_%2812%29%5D二十面体的三维稀土钼酸盐骨架的合成、结构及荧光性能%28英文%29.pdf

第39卷第11期2023年11月Vol.39 No.1122092218无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRY收稿日期：20230411。收修改稿日期：20230914。国家自然科学基金(No.21871262，21901242)、福建省自然科学基金(No.2020J05080)、厦门自然科学基金(No.3502Z20206080)、中国科学院重点研究计划(No.ZDRWCN202133)和中国科学院青年创新促进会(No.2021302)资助。通信联系人。Email：，基于LnMo12二十面体的三维稀土钼酸盐骨架的合成、结构及荧光性能黄敏1,2,3,4卓著1,2,3陈婷1,2,3,4路自修,2,3王维,1,2,3,4黄有桂,1,2,3,4(1福建师范大学化学与材料学院，福州350002)(2中国科学院福建物质结构研究所，中国科学院功能纳米结构设计与组装重点实验室，福建省纳米材料重点实验室，福州350002)(3中国科学院海西研究院厦门稀土材料研究所，稀土光电功能材料厦门重点实验室，厦门361021)(4中国科学院大学福建学院，福州350002)摘要：通过缓慢蒸发溶剂法合成了2例新的三维稀土钼酸盐：Ln(H2O)33LnMo12O42xH2O，其中Ln=Eu(1)、Tb(2)，x=7(1)，10.17(2)。这2种稀土钼酸盐中都含有新颖的二十面体LnMo12O42构建单元，该单元通过与LnO9多面体进一步连接形成三维网络。光致发光测试表明，化合物1和2显示出明显不同的发射特征，这与Eu3+和Tb3+离子的不同能级跃迁密切相关。化合物1表现出较强的红色发射(CIE色度坐标为(0.66，0.33)、高发光强度、较大的荧光量子产率(约60%)，对应于从5D0到7FJ(J=4、3、2、1、0)的跃迁；化合物2表现出浅绿色发射(CIE色度坐标为(0.34，0.60)，对应从5D4到7FJ(J=6、5、4、3)的能级跃迁，其发光强度较弱和荧光量子产率较低(约20%)。有趣的是，一定量的Tb3+引入和大量溶剂分子的存在导致化合物2发生部分荧光猝灭，但对化合物1的荧光几乎没有影响。关键词：稀土钼酸盐；晶体结构；光致发光；荧光淬灭；配位化学；荧光粉中图分类号：O614.33+8；O614.341文献标识码：A文章编号：10014861(2023)11220910DOI：10.11862/CJIC.2023.176Synthesis,crystal structure,and luminescence properties of threedimensionalrare earth molybdate framework based on LnMo12 icosahedronHUANG Min1,2,3,4ZHUO Zhu1,2,3CHEN Ting1,2,3,4LU ZiXiu,2,3WANG Wei,1,2,3,4HUANG YouGui,1,2,3,4(1College of Chemistry and Materials Science,Fujian Normal University,Fuzhou 350002,China)(2CAS Key Laboratory of Design and Assembly of Functional Nanostructures,Fujian Provincial Key Laboratory of Nanomaterials,Fujian Institute of Research on the Structure of Matter,Chinese Academy of Sciences,Fuzhou 350002,China)(3Xiamen Key Laboratory of Rare Earth Photoelectric Functional Materials,Xiamen Institute of Rare Earth Materials,Haixi Institutes,Chinese Academy of Sciences,Xiamen,Fujian 361021,China)(4Fujian College,University of Chinese Academy of Sciences,Fuzhou 350002,China)Abstract:Two new 3D rareearth molybdate frameworks,Ln(H2O)33LnMo12O42xH2O,where Ln=Eu(1),Tb(2);x=7(1),10.17(2),have been synthesized by slow evaporation.Both of these rare earth molybdate frameworks have anew rareearthcentered icosahedron LnMo12O42 building unit,which is further connected to adjacent ones byLnO9 polyhedra to form a 3D network.Photoluminescence tests reveal that 1 and 2 exhibited different emissionproperties,which are caused by the forbital energy levels of Eu3+and Tb3+.1 exhibited bright red emissions(CIE无机化学学报第39卷chromaticity coordinates:(0.66,0.33)corresponding to the transition from5D0to7FJ(J=4,3,2,1,0),with high luminescent emission intensity and high quantum yield(about 60%).2 exhibited light green emissions(CIE chromaticitycoordinates:(0.34,0.60)corresponding to the transition from5D4to7FJ(J=6,5,4,3),with lower luminescent emission intensity and quantum yield(about 20%).Interestingly,the introduction of Tb and the presence of a large number of solvent molecules in compound 2,both lead to partial fluorescence quenching but have little effect on the fluorescence properties of 1.CCDC:2254280,1;2254281,2.Keywords:rareearth molybdate;photoluminescence;crystal structure;fluorescence quenching;phosphor0IntroductionRareearth molybdates possess interesting structures because of the flexibility of coordination numberand geometry of both Ln3+and Mo6+ions15.The diversestructures of rare earth molybdates lead to unique physical and chemical properties,such as magnetism,luminescence,and catalysis510.Among various properties,the photoluminescence properties of rareearth molybdates are of particular interest and have been widelyinvestigated.As we know,rareearth ions with rich energy levels,as the most popular activators,enable luminescent emissions over the ultraviolet visible near infrared(UVVisNIR)spectral region via ff or dftransitions.The 4f orbitals of Ln3+ions are shielded bythe 5s25p6subshells and therefore give highly intensivenarrowband emissions,making them attractive for awide range of applications such as displays,luminescent sensors,and medical probes for clinical use.Famous examples include the Eu3+and Tb3+based compounds with red(5D07FJtransition)and green(5D47FJtransition)luminescence,respectively.On the other hand,molybdates generally have goodchemical stability,thermal stability,luminescent properties,mechanical properties,and thermal conductivity1113.The molybdate matrix also has a strong and widecharge absorption band in the near ultraviolet range.Under ultraviolet excitation,the energy is transferredto the active ions through nonradiative transitions.Bycombining rare earth ions and Mo6+into rare earthmolybdates,excellent performance can be realized.Forexample,Ln2MoO6(Ln=rare earth)14,Ln2Mo2O915,Ln2Mo3O1216,Ln2Mo5O1817,Ln2Mo4O1518,Ln4Mo7O2719,Ln6MoO1220,Ln6Mo10O3921,Nb12.4MgMo13O3622,andLnEuMo2O823(A=alkali metal)were found to have different structural characteristics and fluorescence performances.Up to now,the synthesis of new rareearthmolybdates with well designed structures is still animportant research topic.This is because the chemicaland physical properties of a material closely depend onits composition,structure,crystalline phase,shape,particle size,and dimensionality2427.It is therefore important to obtain new rare earth molybdates exhibitinggood luminescence performances,to explore the relationship between crystal structure and luminescenceperformance.In this work,two new 3D rare earth molybdateframeworks,Ln(H2O)33LnMo12O42xH2O,where Ln=Eu(1),Tb(2);x=7(1),10.17(2),were synthesized forthe first time via a facile slow evaporation method.Thecrystal structures were determined and the luminescence properties were investigated.1Experimental1.1Starting materials and instrumentsAll chemicals,including Tb(NO3)36H2O(AdamasCo.,Ltd.,purity greater than 99.99%),Eu(NO3)35H2O(AdamasCo.,Ltd.,puritygreaterthan99.99%),Co(NO3)26H2O(Adamas Co.,Ltd.,99%),thiodiglycolicacid(Bidepharm Co.,Ltd.,98%),and Na2MoO46H2O(Bidepharm Co.,Ltd.,97%),HCl(36%38%，12 molL-1,Greagent)were used as received without furtherpurification.PowderXraydiffraction(PXRD)datawererecorded on a Rigaku miniflex 600 powder Xray diffractometer(Cu K,=0.154 184 nm)at room temperature(40 kV,15 mA,2=350).The IR spectrum wasrecorded on a Thermo Fisher Nicolet iS 50IR spectrophotometer in a range of 4004 000 cm-1.Thermogravi2210第11期metric analysis(TGA)was carried out on a TGA 50thermogravimetric analyzer from 30 to 800 in anargon atmosphere with a heating rate of 5 min-1.The emission spectra and excitation spectra were collected at room temperature using a spectrometer(FLS980,Edinburgh Instruments)equipped with both continuous(450 W)and microsecond pulsed xenon(Xe)lamps,with the detection of emission spectra to 2 100nm and timecorrelated singlephoton counting lifetimemeasurements as short as 30 ps.Measurements of theemission spectra were conducted using excitation atthe strongest excitation wavelength,i.e.,328 nm for 1and 276 nm for 2.The photoluminescence decay spectra were collected on the same spectrofluorometer withan excitation wavelength of 350 nm as the lightingsource.Quantum efficiency was measured at room temperature with an FLS 980 spectrometer.It is defined asthe ratio between the number of photons emitted by theLn3+ion to the number of those absorbed and could becalculated according to Eq.1:=AR/(AR+ANR),where ARand ANRare the radiative and nonradiative transitionprobabilities,respectively.1.2Preparation of compounds 1 and 2For compound 1,a mixture of Eu(NO3)36H2O(0.504 g,1.13 mmol),Co(NO3)26H2O(0.366 1 g,0.90mmol),thiodiglycolic acid(0.134 9 g,0.90 mmol),andNa2MoO46H2O(0.153 0 g,0.63 mmol)was dissolvedin a mixed solvent of HCl(2 mL)and H2O(8 mL).Thesolution was stirred at room temperature for 5 h andthen put in a 20 mL vial covered with a piece of parafilm with a large number of pinholes.The vial was keptat 100 for 2 d.Colorless blockshaped crystals of 1were isolated by filtration(Yield:75%based on Eu).Compound 2 was prepared in a procedure similarto that of 1,except that Eu(NO3)36H2O was replacedby Tb(NO3)35H2O(Yield:80%based on Tb).1.3Crystallographicdatacollectionandstructure refinementSingle crystals were mounted on a loop using viscous hydrocarbon oil for singlecrystal Xray diffraction measurements.The data were acquired by using aBruker D8 APEX CCD diffractometer with Mo Kradiation(=0.071 073 nm)at 200(2)K.Subsequently,data were directly integrated with the SAINT program28.The structure was solved by direct methodsand refined by a fullmatrix leastsquares techniquebased on F2using SHELXL2017 within Olex229.ThePLATON program30was used to verify the symmetry ofthe structure.All nonhydrogen atoms were refined anisotropically.The contribution of the disordered solventmolecules was subtracted from the reflection data bythe SQUEEZE method as implanted in the PLATONprogram.Selected crystallographic data and structuredetermination parameters for compounds 1 and 2 aregiven in Table 1.Selected bond distances and bond angles of 1 and 2 are listed in Table 2 and 3.CCDC:2254280,1;2254281,2.Table 1Crystallographic data of compounds 1 and 2ParameterFormulaFormula weightCrystal systemSpace groupa/nmb/nmc/nmV/nm3ZDc/(gcm-3)F(000)Reflection collected,uniqueRint1Eu4Mo12O58H322 719.37TrigonalR3c1.817 57(3)1.817 57(3)2.426 79(9)6.943 0(3)63.9027 51244 522,1 4120.059 32Tb4Mo12O61.17H38.342 804.16TrigonalR3c1.725 29(3)1.725 29(3)2.536 54(6)6.538 8(3)63.9947 14017 190,1 6390.020 0黄敏等：基于LnMo12二十面体的三维稀土钼酸盐骨架的合成、结构及荧光性能2211无机化学学报第39卷2Results and discussion2.1Crystal structures descriptionSinglecrystal Xray diffraction shows that compounds 1 and 2 are isostructural.As a representativeexample,we only illustrate the structural features of 1in detail.1 crystallizes in the trigonal crystal system(space group:R3c)with the formula of Eu(H2O)33EuMo12O427H2O.In the asymmetric unit,the Eu,Mo,and O atoms occupy two,two,and eleven crystallographically unique positions,respectively.In the structure,the trivalent cations Eu3+are twelvefold and ninefold coordinated with O atoms,resulting in Eu1O12and Eu1O9 polyhedra(Fig.1a and 1e),respectively.The Mo6+ions are all sixcoordinated with O atoms toform distorted MoO6 octahedra(Fig.1b).The EuOdistances in the Eu1O12 polyhedra lie in a range of0.250 10.252 7 nm with an average bond distance of0.251 4 nm,while the EuO distances in the Eu2O9polyhedra ranges from 0.242 9 to 0.244 9 nm.The disParameterCompleteness/%GOF on F2R1,wR2I2(I)R1,wR2(all data)199.91.1000.022 9,0.052 90.027 8,0.056 9297.31.1830.029 3,0.085 90.029 3,0.085 9Continued Table 1Table 2Selected bond lengths(nm)for compound 1Eu1O1#1Eu1O1#2Eu1O1#3Eu1O1#4Eu1O1#5Eu1O1Eu1O6#2Eu1O6#4Eu1O6#5Eu1O6#1Eu1O6#30.250 1(4)0.250 1(4)0.250 1(4)0.250 1(4)0.250 1(4)0.250 1(4)0.252 7(4)0.252 7(4)0.252 7(4)0.252 7(4)0.252 7(4)Eu1O6Eu2O2Eu2O7#6Eu2O7Eu2O8#4Eu2O8#7Eu2O10#8Eu2O10#3Eu2O11Eu2O11#6Mo1O10.252 7(4)0.243 6(9)0.242 9(6)0.242 9(6)0.244 9(4)0.244 9(4)0.244 6(4)0.244 6(4)0.244 9(4)0.244 9(4)0.189 5(4)Mo1O1#2Mo1O4Mo1O6#4Mo1O10Mo1O11Mo2O1#2Mo2O3Mo2O4Mo2O6#4Mo2O6Mo2O80.225 5(4)0.193 2(4)0.225 9(4)0.171 5(4)0.172 0(4)0.227 5(4)0.169 4(4)0.195 3(4)0.225 1(4)0.191 6(4)0.173 1(4)Symmetry codes:#1:-x+4/3,-y+2/3,-z+2/3;#2:x-y+1/3,x-1/3,-z+2/3;#3:y+1/3,-x+y+2/3,-z+2/3;#4:-x+y+1,-x+1,z;#5:-y+1,x-y,z;#6:x-y+2/3,-y+4/3,-z+5/6;#7:y+2/3,x+1/3,-z+5/6;#8:x+1/3,x-y+2/3,z+1/6.Table 3Selected bond lengths(nm)for compound 2Tb1O4Tb1O4#1Tb1O1Tb1O2Tb1O2#1Tb1O3Tb1O3#1Tb1O5#1Tb1O5Tb2O8Tb2O8#20.244 5(5)0.244 5(5)0.239 0(10)0.247 6(7)0.247 6(7)0.235 5(5)0.235 5(5)0.245 5(5)0.245 5(5)0.251 9(5)0.251 9(5)Tb2O8#3Tb2O8#4Tb2O8#5Tb2O8#6Tb2O6#6Tb2O6Tb2O6#3Tb2O6#4Tb2O6#5Tb2O6#2Mo1O80.251 9(5)0.251 9(5)0.251 9(5)0.242 9(6)0.249 4(5)0.249 4(5)0.249 4(5)0.249 4(5)0.249 4(5)0.249 4(5)0.225 7(5)Mo1O6Mo1O6#3Mo1O7Mo1O4#3Mo1O5Mo2O8Mo2O8#4Mo2O6Mo2O7Mo2O9Mo2O3#20.223 9(4)0.188 7(5)0.194 5(5)0.173 7(5)0.171 8(5)0.221 0(5)0.228 3(5)0.194 9(5)0.194 9(5)0.169 8(6)0.172 9(5)Symmetry codes:#1:-x+2/3,-x+y+1/3,-z+11/6;#2:y+1/3,-x+y+2/3,-z+5/3;#3:x-y+1/3,x-1/3,-z+5/3;#4:-x+y+1,-x+1,z;#5:-x+4/3,-y+2/3,-z+5/3;#6:-y+1,x-y,z.2212第11期torted MoO6 polyhedral exhibits a wide variation ofMoO distances(0.169 40.227 5 nm).These valuesare in agreement with those of other rareearth molybdates reported previously3133.The structure of 1 features a complicated 3D network composed of EuMo12O42 and Eu1O9 polyhedra.Specifically,one Eu1O12 and twelve MnO6 are connected via 4O or 2O atoms to build a Eucenteredicosahedron EuMo12O42 with the Eu1 at the center(Fig.1c and 1d).The EuMo12O42 polyhedron connectswith six other EuMo12O42 polyhedra via six Eu2O9polyhedra,forming a EuMo12O427 Eu2O96 framework(Fig.1f)that represents the overall 3D structure of1(Fig.2).By treating the EuMo12O42 and Eu2O9 polyhedra as the nodes and linkers(Fig.2a),respectively,the structure of 1 can be simplified as a pcu networkwith a Schlfli symbol of 4669(Fig.2b).It is worth noting that the Eucentered icosahedron EuMo12O42 secondary building units are rarely seen.Similar structures are only observed in a few noble metal nanoclusters34.The only rareearth molybdates with a similarstructure are Gd(H2O)33GdMo12O423H2O35.Fig.1Molecular structure composition of compound 1:(a)Eu1O12 polyhedron;(b)MoO6 polyhedron;(c)EuMo12O42 polyhedron;(d)atomic skeleton structure of centered icosahedron EuMo12O42;(e)Eu2O9 polyhedron;(f)7EuMo12O42+6Eu2O9 frameworkSymmetry codes:#3:y+1/3,-x+y+2/3,-z+2/3;#4:-x+y+1,-x+1,z.Fig.2(a)Topology analysis of the structure of compound 1;(b)pcu network of compound 12.2PXRD analysisFig.3 shows the observed PXRD patterns of thepowder samples of compounds 1 and 2,together withthe calculated ones from their single crystal structures.The observed PXRD patterns were in agreement withthe simulated patterns,further confirming that theobtained samples are of good purity.2.3IR spectroscopyThe FTIR spectra of the powder samples of compounds 1 and 2 in a range of 4004 000 cm-1are shownin Fig.4.Compounds 1 and 2 exhibited IR spectra withsimilar absorption features,indicating the presence ofsimilar functional groups in the two structures.Specifically,significant absorptions were observed at 1 608黄敏等：基于LnMo12二十面体的三维稀土钼酸盐骨架的合成、结构及荧光性能2213无机化学学报第39卷and 3 291 cm-1for 1,while similar absorption peaks at1 610 and 3 300 cm-1were observed for 2.These aretypical OH stretching vibrations of the water molecules in the structure.The bands at 855 cm-1(for 1)and 857 cm-1(for 2)can be assigned to the OMoOstretching vibrations of the MoO6 octahedra.Thepeaks observed in the IR spectra are consistent withthose of the other synthetic compounds and mineralscontaining MoO6 and H2O3639.2.4TG analysisTo study the thermal stability of compounds 1 and2,the TG curves of polycrystalline samples were studied(Fig.5).In Fig.5a,we can see that compound 1exhibited good thermal stability,with less than 8.2%weightloss up to 233.28.This is likely attributed tothe loss of free H2O molecules.In a temperature rangeof 233.28410.91,only a small amount of weightloss was observed(Fig.5a),which may be caused by thedetachment of coordinated water molecules.Similar tocompound 1,compound 2 exhibited a signif