Synthesis And Properties Of Rare Earth Doped Re₃PO₇?Re=La,Y,Gd? Fluorescent Material

Rare earth phosphates are high-efficiency fluorescent materials.There had been widely investigated in the field of lighting and display.In the present studies,most of researches were forced on the synthesis and properties of rare earth doped orthophosphates and oxides.However,there is still a lack of studies in the preparation and properties of rare earth doped non-orthophosphates.While rare earth doped non-orthophosphates easily formed chain or ring structure,which greatly increases the distance between rare earth ions in crystal latticeand reduces the energy transfer efficiency between rare earth active ions,meaning that the rare earth doped non-orthophosphates may be display excellent luminescence properties,especially for high concentration doped matrix.The Eu3+ doped La3PO7 crystals were synthesized by a co-precipitation method.The influences of the pH of the solution,the calcination temperature,the calcination time,the mole ratio of Re(Re=La and Eu)to P(n(La+Eu)/n(P)),and the concentration of Eu3+ on the phase structures,luminescence properties and particle size distribution of the synthetic La3PO7:Eu3+ samples wereinvestigated.The results show that the optimum synthesis conditions of the as-prepared of Eu3+doped La3PO7nano-materials by co-precipitation method could be summarized as follows: the pH of the solution is 10,the calcination temperature is 900 oC,the calcination time is 25 h,the mole ratio of Re(Re=La and Eu)to P(n(La+Eu)/n(P))is 3:1,and the doping content is 4%(mole fraction).The results show that the particle size distribution of the as-prepared samples followed a normal distribution with a mean particle size of about 626.2 nm.The emission spectra are derived from the 5D0-7F1,5D0-7F2,5D0-7F3 and 5D0-7F4 transitions of Eu3+ ions.The photoluminescence spectra show a dominated red emission peak located at 617 nm under 280 nm light excitation,which originating from the5D0-7F2 transition of Eu3+ ions,confirming that the doping Eu3+ ions replace the La3+ ions at the non-inversion symmetric centers in La3PO7 crystal lattice.The concentration quenching phenomenon was observed when the doping content was over 4%(mole fraction),and the concentration quenching mechanism was caused by the exchange interaction of Eu3+ ions.The Tb3+ doped Y3PO7 samples were prepared by a co-precipitation method.The effects ofthe calcination temperature,the pH of the solution,the calcination time,the mole ratio of Re(Re=Y and Tb)to P(n(Y+Tb)/n(P)),and the doping concentration of Tb3+ions on the phase structures,luminescence properties and particle size distribution of the as-synthetized samples were studied.The results show that the optimum synthesis conditions as follows: the calcination temperature is 900 oC,the pH of the solution is 6.7,the calcination time is 25 h,the mole ratio of Re(Re=La and Eu)to P(n(La+Eu)/n(P))is 7:3,and the doping content is6 %(mole fraction).The pH of the solution and the mole ratio of Re(Re=La and Eu)to P(n(La+Eu)/n(P))has a significant effect on the phase structure of the sample.The results show that the samples obtained under these conditions are pure phase Tb3+ doped Y3PO7 crystals.Under UV light excitation,the as-prepared samples emit the characteristicgreen light of Tb3+ ions at 545 nm.There are a series of excitation peaks derived from the absorption of 4f7-5d1 transition,O2--Tb3+ charge transfer band,and the 7F6-5H6,7F6-5H7,7F6-5L7,7F6-5D2,7F6-5G5,7F6-5D3 and 7F6-5D4 of the 4f-4f transition.In addition,a series of emission peaks are derived from the5D4-7F6,5D4-7F5,5D4-7F4,5D4-7F3 transitions of Tb3+ions located at 490 nm,545nm,588 nm,and 623 nm,respectively.The concentration quenching phenomenon was observed when the doping content was over 6 %(mole fraction).The Eu3+,Tb3+,Sm3+,Dy3+and Ce3+ doped/co-doped Re3PO7(Re=La,Gd)luminescent materials were obtained by a co-precipitation method.The phase structure and properties of the as-prepared samples were also researched.The results show that the rare earth ions doped Gd3PO7 and La3PO7were pure phase with monoclinic crystal.The slight contents of the rare earth ions doped in the lattice did not obviously change the phase structure of the matrix.The emission peaks of the Eu3+ doped Gd3PO7 luminescent materials are derived from the 5D0-7F1,5D0-7F2,5D0-7F3 and 5D0-7F4 transitions of Eu3+.The concentration quenching phenomenon was observed when the doping content was over 8 %(mole fraction).The concentration quenching mechanism was caused by the exchange interaction of Eu3+ ions.The emission bands of Sm3+ doped Gd3PO7 luminescent materials are origined from the 4G5/2-6H5/2,4G5/2-6H7/2,and4G5/2-6H9/2 transitions of Sm3+.The concentration quenching phenomenon was also presented when the doping content was over 1 %(mole fraction).The concentration quenching mechanism was caused by the exchange interaction of Sm3+ions.For the Dy3+ doped La3PO7 luminescent materials,the emission peaks are derived from the 4F9/2-6H13/2 transitions of Dy3+ions.The concentration quenching phenomenon was observed when the doping content was over 3 %(mole fraction),and the concentration quenching mechanism was caused by the exchange interaction of Dy3+ions.The emission bands of Ce3+ doped La3PO7 crystals are derived from the 5d-2F5/2 transitions of Ce3+ ions.The concentration quenching phenomenon was observed when the doping content was over 1.5 %(mole fraction).In the emission spectra of the Gd3PO7:0.2%Ce3+,x%Tb3+ samples,a series of emission peaks which derived from the5D4-7F6,5D4-7F5,5D4-7F4,5D4-7F3 transitions of Tb3+ can be observed.And the quenching concentration is 5%(mole fraction)for the Gd3PO7:0.2%Ce3+,x%Tb3+ samples.