Sacrifical Template Synthesis And Up/Down Conversion Luminescence Properties Of High Performance Rare Earth Fluoride Phosphors

At present,rare earth fluorides are widely used in phosphor matrix because of their low phonon energy and high emission energy.Fluoride phosphors doped with rare earth ions have attracted researchers'attention because of their adjustable spectrum,wide coverage and high application prospect in up/down conversion luminescence.In this work,sulfate-type rare earth layered compounds((La,RE)₂(OH)₄SO₄·2H₂O(RE=Gd,Eu,Tb,Sm,Er,Ho,Tm and Yb)were used as new templates to synthesis rare earth fluoride,as the relevant synthesis principles were explained.The phase transformation in the reaction process and the luminescence of the obtained products were studied by self-sacrifice template method.The specific work is as follows:(1)(La_0.95RE_0.05)F₃(RE=Eu,Tb and Sm)was prepared with the NH₄F by self-sacrificetemplatehydrothermalmethod,whilethe(La_0.95RE_0.05)₂(OH)₄SO₄·n H₂O(RE=Eu,Tb and Sm)precursor was synthesized by hydrothermal method.The down-conversion fluorescence properties of the(La,RE)F₃with hexagonal phase were studied.The results show that(La_0.95RE_0.05)F₃(RE=Eu,Tb and Sm)phosphors have the strongest emission peaks at 589 nm,539 nm and 591 nm,which belong to the ⁵D₀?⁷F₁(589 nm)transition of Eu³⁺,⁵D₄?⁷F₅(539 nm)transition of Tb³⁺and ⁴G_5/2?⁶H_7/2(591 nm)of Sm³⁺,respectively.The lifetimes of these phosphors are 1.36 ms(Eu),0.87 ms(Tb)and 2.17 ms(Sm)and the CIE color coordinate diagram of the phosphors are(0.60,0.39)(Eu),(0.33,0.57)(Tb)and(0.55,0.44)(Sm),respectively.(2)Three upconversion fluorescent materials(La_0.97Yb_0.02RE_0.01)F₃(RE=Er,Ho and Tm)were synthesized with Ho,Er and Tm as activators and Yb as sensitizer on the basis of the above results.The phase conversion process and up-conversion fluorescence properties of the products were studied and the results show that(La_0.97Yb_0.02Er_0.01)F₃has the strongest emission peak at 656 nm,which belongs to the⁴F_9/2?⁴I_15/2transition of Er³⁺,and the fluorescence lifetime of this emission peak is about 1.466 ms;(La_0.97Yb_0.02Ho_0.01)F₃has the strongest emission peak at 642 nm,which belongs to the transition of ⁵F₅?⁵I₈of Ho³⁺,and the fluorescence lifetime of this emission peak is about 0.745 ms;(La_0.97Yb_0.02Tm_0.01)F₃has the strongest emission peak at 804 nm,which belongs to the ³H₄?³H₆transition of Tm³⁺.(3)(La_0.95-xGd_xEu_0.05)OF(x=0-0.95)were prepared with the NH₄F by self-sacrificetemplatehydrothermalmethod,whilethe(La_0.95-xGd_xEu_0.05)₂(OH)₄SO₄·n H₂O(x=0-0.95)precursors were synthesized by hydrothermal method.The(La_0.95-xGd_xEu_0.05)OF phosphors were obtained by calcination at different temperatures with the precursors of(La_0.95-xGd_xEu_0.05)(OH)₂F crystal and the performances of their down-conversion fluorescence were studied.The results show that the strongest transition in the fluorescence spectra of the precursors(La_0.95-xGd_xEu_0.05)(OH)₂F appear at 613 nm,which belongs to the ⁵D₀?⁷F₂transition of Eu³⁺.The fluorescence decay of this transition has a behavior with single exponential function,and the fluorescence lifetime is about between 1.11 ms with 0.95 ms.The CIE color coordinate diagrams are between(0.61,0.38)and(0.62,0.36),which are located in the orange-red region.The(La_0.95-xGd_xEu_0.05)OF(x=0.95,0.75 and 0.3)phosphors have the strongest emission peak at 608 nm,which originates from⁵D₀?⁷F₁transition of Eu³⁺.the fluorescence lifetime of phosphor is about 2.00 ms,1.42 ms and 1.49 ms respectively and IE color coordinate diagrams are about(0.65,0.35).(4)The three upconversion phosphors(La_0.77Gd_0.2Yb_0.01RE_0.02)OF(RE=Er,Ho and Tm)were synthesized with Ho,Er and Tm as activators and Yb as sensitizer on the basis of the above results.The result shows that(La_0.77Gd_0.2Yb_0.01Er_0.02)OF has the strongest green emission peak at 546 nm,which belongs to the 4f-4f(²H_11/2/⁴S_3/2?⁴I_15/2)transition of Er³⁺,the fluorescence lifetime is about 0.36 ms under the excitation of 0.65 W power at room temperature;(La_0.77Gd_0.2Yb_0.01Ho_0.02)OF has the strongest green emission peak at 544nm,which belongs to the ⁵S₂?⁵I₈transition of Ho³⁺,the fluorescence lifetime is about 0.25 ms under the excitation of 0.65 W power at room temperature;(La_0.77Gd_0.2Yb_0.01Tm_0.02)OF has the strongest near infrared emission peak at 794 nm,which belongs to the ³H₄?³H₆transition of Tm³⁺,the fluorescence lifetime is about 0.32 ms under the excitation of 1.2 W power at room temperature.