| 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(α-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(α2-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[α2-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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