| In this dissertation,it is oriented to the preparations and functions of antimonotungstate(AT)-based rare-earth(RE)derivatives and isopolytungtate(IPOT)-based RE derivatives,thus,three types of polyoxotungtate(POT)-based RE derivatives have been constructed in aqueous solution.The first type is RE and Sb-oxo-cluster simultaneously bridging ATs,the second type is acetate-decorated tetrahedral {WO4}-derecting tri-RE substituted trimeric ATs and the third type is a double-oxalate-bridging tetra-RE substituted IPOT with a 3-D porour framework They have been characterized by various physicochemical measurements and photoluminescence properties have been systematically investigated.Their intramolecular luminescence mechanisms have been also elucidated.Moreover,heteronuclear RE co-doped POTs have been prepared and their tuneable luminous performances have been studied.The dissertation provides not only new synthetic ideas and methods for preparing novel AT-based RE derivatives and IPOT-based RE derivatives,but also valuable theoretical and experimental foundations for the optical applications of POT-based RE derivatived materialsThis dissertation is divided into five chaptersChapter 1:This chapter summarizes the research developments of AT-based RE derivatives/IPOT-based RE derivatives involving their structural features and relative properties.Simutaneously,some examples on photoluminescence properties of representive POT-based RE derivatives have been also enumerated to demonstrate their great potentials in optic applicationsChapter 2:Based on the synthetic ideas:organoamine cations can act as solubilizers to improve the reaction behavior between POTs and RE ions;the main-group Sb3+ions can perform as effective metal linkers;and the trivacant Keggin-type[B-?-SbW9O33]9-fragment has a strong affinity to RE ions,four novel RE and Sb-oxo-cluster simultaneously bridging ATs[H2N(CH3)2]8Na6H8{[RE4(H2O)6 Sb6O4](B-a-SbW10O37)2(B-?-SbW8O31)2}·24H2O(RE=Dy3+,Er3+,Y3+,Ho3+,Tb3+)(1-4)have been triumphantly constructed.Their tetrameric polyoxoanions are all established by two[B-?-SbW10O37]11-and two[B-?-SbW8O31]11-segments encapsulating a RE-Sb heterometal[RE4(H2O)6Sb6O4]22+cluster.Under the excitation at 268 nm derived from the O?W(1A1g?1T1u)LMCT absorption in AT segments,the RE ions in 1 and 2 can absorb the emission energy(3Tiu?1A1g)from AT segments,giving rise to the sensitization of AT segments to the emission of RE ions in 1 and 2.Through the sensitization of AT segments,the emission intensities are increased and lifetimes are prolonged in 1 and 2.Photoluminescence and energy transfer(ET)measurements indicate that Dy3+ions in 1 can obtain more energy from AT segments than to Er3+ions in 2.Furthermore,the sensitization effects of AT segments to different f-f transitions of RE ions can be effectively influenced by the matched degree betweeen the 1A1g?1T1u emission transition and f-f emission transitions of RE ions.It seems that the better energy level match of 3Tiu?1A1g transition of AT segments with f-f emission transitions of RE ions will lead to a stronger sensitization effect.The CIE diagrams of 1 and 2 give out varied emission colors under O?W LMCT excitation and f-f excitation in 1 and 2.Chapter 3:With the help of the synthetic ideas that carboxyl-containing organic ligands can play a significant role of structure decorators and the four-coordinated{WP4} tetrahedron can act as structure-directing agent to directing the formation of polyoxoanions,four acetate-decorated tri-RE tetrahedral {WO4}-directing substituted trimeric ATs Na17{(WO4)[RE(H2O)(Ac)(B-?-SbW9O31OH)2)]3}·50H2O[RE=Eu3+,Dy3+,Ho3+,Gd3+)(5-8)were isolated.Interestingly,a tetrahedral {WO4} group plays a significant structure-directing template role in the formation of their polyoxoanions.With regard to luminescence properties,by changing the excitation wavelength,it is available to switch emission colors from orange to red for 5,blue to green for 6 and blue to yellow for 7.Under the O?W LMCT excitation,energy transfer from AMT fragments to Eu3+,Dy3+and Ho3+ions occurs because RE3+ions can absorb energy from O?W LMCT emission of AT segments.The temperature-dependent luminescence behaviors(25-720?)of 5 together with auxiliary emitting photographs illustrate that the growing emission in temperature range of 25-100?results from the loss of lattice water molecules,the decline of emission between 100 and 320? may be because crystals become amorphous powders,the slow emission decay(220-320?)is due to the case that the emission enhancement derived from the removal of water ligands on Eu3+ions in some degree compensates for the decline of emission intensity,the sharp decrease of emission(320-520?)may result from the change of coordinate environment of Eu3+ions,and the weak recovery of emission(620-720?)may be ascribed to the formation of new phase Nao.5Euo.5WO4.This work lays a significant foundation for preparing novel POM-based luminescent materials.Chapter 4:An acetate-decorated tri-Tb3+substituted trimeric ATs Na17{(WO4)[Tb(H2O)(Ac)(SbW9O31(OH)2)]3}·50H2O(Tb3W28)has been successfully synthesized.The capping {WO4} tetrahedron has a key role of structure direction,it drives three Tb3+ions and three[B-?-SbW9O33]9-fragments to aggange in a regular triangle mode.The single-phase Eu3+/Tb3+/Dy3+codoped system based on Tb3W28 has been firstly prepared.When the red emitter Eu3+,yellow emitter Dy3+and Gd3+ions are codoped into Tb3W28 to substitute Tb3+ions for the research of energy transfer(ET)mechanism among Dy3+,Tb3+and Eu3+ions and the emission color tunable property,the structure of polyoxoanions has remained integrally.Upon the 6H15/2?4I13/2 excitation of Dy3+at 389 nm,the ET mechanism(Dy3+?Tb3+)has been confirmed as a nonradiative dipole-dipole interaction.Upon the 7F6?5L10 excitation of Tb3+at 370 nm,the ET mechanism(Tb3+?Eu3+)is a non-radiative quadrupole-quadrupole interaction.Under the excitation at 389 nm,the two-step successive Dy3+?Tb3+?Eu3+ET process has been proved in Eu3+/Tb3+/Dy3+codoped Dyi.2Tb32Eu0.03Gd1.77-3zW28 system.Through switching the excitation wavelengths for Dyi.2Tbi.2Eu0.03Gd0.57W28,the emission color has varied from blue to yellow,in which a near-white-light emission has been obtained upon the excitation at 378 nm.Chapter 5:In line with the synthetic idea that multi-carboxyl-containing organic ligands can connect with multiple POT fragments,a double-oxalate-bridging tetra-Gd3+containing divacant Lindqvist dimeric IPOTs Na10[Gd2(C2O4)(H2O)4(OH)W4O16]2·30H2O(Gd4Ws)was obtained based on the reaction of Na2WO4·2H2O,H2C2O4 and GdCl3 in aqueous solution.Its dimeric polyoxoanion is established by two divacant Lindqvist-type[W4O16]8-segments connected by a rectangular tetra-nuclearity[Gd4(C2O4)2(H2O)8(OH)2]6+cluster.Notably,neighboring trinuclear[Na3O4(H2O)11]5-clusters are interconnected to construct a picturesque 1-D sinusoidal Na-0 cluster chain.The most outstanding characteristic is that 1-D sinusoidal Na-0 cluster chains combine[Gd2(C2O4)(H2O)4(OH)W4O16]210-polyoxoanions together,giving rise to an intriguing 3-D extended porous framework.The red emitter Eu3+ions and green emitter Tb3+ions are firstly co-doped into Gd4Ws to substitute Gd3+ions for the exploration of energy transfer(ET)mechanism between Eu3+and Tb3+ions and color-tunable PL property in isopolytungtate system.The PL emission spectra and decay lifetime measurements of the Eu3+/Tb3+co-doped Gd4Ws system illustrate that under the excitation at 370 nm,Tb3+ions can transfer energy to Eu3+ions.When the molar concentration of Tb3+ions is fixed as 0.9 and that of Eu3+ions gradually increases from 0.01 to 0.08,the calculated ET efficiency(?ET)from Tb3+to Eu3+ions increases from 7.9%for Gd0.36Tb3.6Eu0.04W8 to 67.3%for Gd0.08Tb3.6Eu0.32W8.The energy transfer mechanism(Tb3+?Eu3+)is a non-radiative dipole-dipole interaction.Furthermore,upon the excitation at 370 nm,Eu4W8 and Tb4Ws show the visible red and green emission lights,respectively When co-doping trace amounts of Eu3+ions in Tb4Ws,under the excitation at 370 nm,Tb3.92Eu0.08W8 displays near white light emission... |
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