| Polyoxometalates(POMs)are well-defined with abundant structural topologies and oxygen-rich surface,which afford lone pair electrons that coordinate to f-and/or d-metal ions to form functionalized POM derivatives.Lanthanides ions(Ln3+)are widely used in several applications(e.g.,magnetic,luminescence)that originate from the unique 4Ff electronic configuration generating a large variety of electronic levels.Ln3+ions can be utilized as a good electron acceptors due to unfilled 5d or 6s orbitals which can accept lone pair of electrons from POM subunits to form covalent bonds,constructing Ln-based POM derivatives.Up to now,Ln-based POM derivatives have drawn considerable interest of researchers because of abundant topologies,sharp characteristic emissions,and long luminescent lifetime,such as catalysis,magnetism,biology,medicine,electro-chemistry and optics.On account of these excellent features and good potential applications of Ln-based POM derivatives,[P2W19069(H2O)]14-and[P2W156]12-precursor were used to synthesize a series of Ln-based POM derivatives,and we also systematically investigated their photoluminescence behaviors.(1)The reported[N(CH3)4]6K3H7[Dy(C4H2O6)(a-PW11O39)]2·27H2O as choosed as the parent Ln-POM to synthesize two series of different ratios of Dy3+/Er3+ and Dy3+/Tm3+ ion doped DyxEr(1-x)-POM and DyxTm(1-x)-POM derivatives which have been well synthesized by various physicochemical analysis.Time resolved emission spectroscopy reasonably approves that the photoexcitation O?M LMCT state of phosphotungstate fragments can effectively sensitize the emission of Ln3+ ions via intramolecular energy transitions.The photostability study reveals that the Dy0.8Er0.2-POM sample on continuous UV irradiation can exhibit a high photoluminescence emission intensity with wonderful stability.The investigations of color-tunable photoluminescence emission revealed that the CIE luminescent color coordinates of DyxTm(1-X)-POM can be tuned from blue to white to yellow by increasing the doping proportion of Dy3+ ion.(2)We choose lacunary K14[P2W19O69(H2O)]·24H2O precursor that can provide abundant POM-fragmented building blocks in solution reacts with LnCl3-6H2O and organic carboxylic acid to successfully synthetize a series of chromophore-Ln-POM derivatives[N(CH3)4]3K2Ln(C7H5O2)(H2O)2(a-PW11O39)]·11H20 and[N(CH3)4]3K2Eu(PHBA)(H20)2(a-PW11O39)]·7H2O.Subsequently,a series of multicenter-Ln analogues[N(CH3)4]3K2EuXTbyTm1-x-y(C7H5O2)(H2O)2(?-PW11O39)·11H2O were synthesized by tuning the molar ratio of Eu3+:Tb3+:Tm3+ ions,and the white-light-emitting behavior can be well tuned by adjusting the molar ratio of Eu3+/Tb3+/Tm3+.The energy transfer between phosphotungstate fragments and Ln3+ ions also have been recorded and carefully studied.The sensing propertis of[N(CH3)4]3K2Eu(PHBA)(H2O)2(a-PW11O39)]·7H2O were peformed on several ions in aqueous solution,and the photolumescnece intensity for sensing Cr3+ ion display a quenching phenomenon and for sensing Ca2+ion display an enhancement signal.(3)Three Ln-based POM derivatives[N(CH3)4]3H8La(H2O)2[Ln2(H2O)7(?2-P2W17O61)2]·17H2O(Ln3+=La3+,Ce3+.,Pr3+)was synthesized by the reactions of[P2W15O56]12-precursor and Ln3+ ions,which were fully characterized by elemental analysis,powder X-ray diffraction,thermogravimetric analyses,Single-crystal X-ray diffraction and IR spectra.Single-crystal X-ray diffraction structural analyses indicate two Ln3+ions as bridges locate defect sites of monolacunary Dawson-type[?2-P2W17O61]10-subunits to construct 1D Z-type chain-like structure,and another one Ln3+ ion connect adjacent 1D Z-type chain to build 2D layer structure.Photoluminescence study reveal that phosphotungstate fragments can not effectively sensitize Pr3+ion in Pr-based POM derivatives,and the reason why the emission intensity of Pr3+ emitting center was so weak can be explained that the radiationless losses via charge-transfer Pr-W state quench the emission of Pr3+ ion. |
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