Preparation And Properties Of Rare Earth Doped Oxygen Phosphate Fluorescent Materials For White LED

In this thesis are focused on the synthesis and properties of rare earth doped Gd₃PO₇,La₇P₃O₁₈ and La₃PO₇ oxyphosphates luminescent materials for white LEDs by co-precipitation method and hydrothermal method.The phase structures,microscopic morphologies and luminescence properties of the prepared samples were characterized by XRD,SEM,FT-IR,UV-Vis DRS and PL.Through experimental research,the conclusions are as follows:Single-host white-light-emitting Gd₃PO₇:Dy³⁺phosphor was synthesized by wet chemical method.The phase structures,morphologies and optical properties of the as-prepared samples were characterized by X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,fourier transform infrared（FT-IR）,and fluorescence spectroscopy.XRD results show that the as-obtained samples are Dy³⁺doped Gd₃PO₇ crystals with monoclinic structure with slight impurity.The PL spectra show that those Gd₃PO₇:Dy³⁺samples emit the characteristic emission bands of Dy³⁺ions at yellow light region(⁴F_9/2→⁶H_13/2)and blue light region(⁴F_9/2→⁶H_15/2),under the excitation with the characteristic excitation band of Gd³⁺ions at 276 nm,indicating that the energy transfer from Gd³⁺to Dy³⁺occur in Gd₃PO₇:Dy³⁺matrix.The luminescence intensities of the samples depend on the p H values and the Dy³⁺doping contents.When the p H is 6.00 and the Dy³⁺doping content is 0.5%,the sample exhibits a relatively high luminescence intensity.The emission color of the Gd₃PO₇:Dy³⁺samples are affected by the Dy³⁺doping contents.The as-synthesized Gd₃PO₇:Dy³⁺sample with 3%can emit white light with coordinates of（0.335,0.345）,implying that Gd₃PO₇:Dy³⁺is a potential single-host white-light-emitting phosphor.The La₇P₃O₁₈:Eu³⁺red luminescence materials were prepared by co-precipitation method.The phase structures,morphologies and luminescence properties of the prepared samples were analyzed by XRD,SEM,FT-IR,PL and other characterization methods.The XRD results show that the obtained samples are La₇P₃O₁₈:Eu³⁺crystals with monoclinic structure containing a small anount of impurity La₃PO₇.Photoluminescence spectra results reveal that under the excitation of 466nm,the La₇P₃O₁₈:Eu³⁺samples emits the characterstic ⁵D₀→⁷F₁ magnetic dipole transition and ⁵D₀→⁷F₂ electric multipole transition emission peaks of Eu³⁺ions at 592 nm and 619 nm,respectively.And the intensity of the emission peak at 619 nm is significantly stronger than that of other emission peaks.The synthesis conditions have an important effect on the pahse strucutre and luminescence properties of the samples.Under the conditions of p H is 0.20,the doping amount of Eu³⁺is 2%,the n（La+Eu）:n（P）is 7:3,the drying temperature of the precursor is 120℃,the drying time is 5 h,and the sintering temperature is 1300℃,the obtained sample exhibit better phase composition,crystallinity and luminescence properties.The La₃PO₇:Pr³⁺luminescence materials with monoclinic structure were prepared by hydrothermal method and co-precipitation method in alkaline environment.p H and Pr³⁺doping content affect the phase structure and photoluminescence properties of the obtained samples.The La₃PO₇:1%Pr³⁺sample prepared by hydrothermal method at p H 12display better luminescence performance,while the La₃PO₇:1.5%Pr³⁺sample sythesized by co-precipitation method at p H 11.5 possess better luminescence properties.The La₃PO₇:Pr³⁺samples obtianed by the two methods can be efficiently excited by 460 nm light and emit the green characteristic emission band at 563 nm for the ³P₀→³H₆ transition of Pr³⁺ions.The hydrothermally synthesized La₃PO₇:Pr³⁺samples have better crystallinity and stronger green light emission than the coprecipitation synthesis sample.The results confirm that the as-synthesized La₃PO₇:Pr³⁺samples can be efficiently excited by the commercial GAN LED blue chip and emit green light,making it as a potential green luminescence material for white LEDs.The La₇P₃O₁₈:Eu³⁺and La₃PO₇:Eu³⁺luminescence materials were prepared by co-precipitation method.In the strong acid environment,the XRD results and fluorescence spectra show that the La₇P₃O₁₈:Eu³⁺crystals prepared in a strong acid condition（p H=0.20）have better crystallinity than La₃PO₇:Eu³⁺crystals.Under the excitation of 466 nm light,the prepared La₇P₃O₁₈:2%Eu³⁺and La₃PO₇:2%Eu³⁺samples both emit red light at 619 nm,and the emission intensity of the La₇P₃O₁₈:2%Eu³⁺sample is significantly stronger than that of La₃PO₇:2%Eu³⁺sample.The calculation results of luminescence color coordinates and luminescence color purities revel that the emission of La₇P₃O₁₈:2%Eu³⁺and La₃PO₇:2%Eu³⁺samples are located in the orange-red light region,and the luminescence color purities are high.The results indicate that the La₇P₃O₁₈:2%Eu³⁺sample can be excited by the commercial GAN LED blue chip and emit red light,which is a potential red light luminescence material for white LEDs.