Preparation And Photoluminescence Properties Of Tungsten/Molybdate Phosphors For WLEDs

With the development of lighting technology,WLEDs have gained much attentions on account of their numerous merits,including high luminous efficiency,longer service time,environmental friendliness and energy conservation.As an important component,the performance of phosphor directly affects the quality of WLEDs.In this thesis,a series of rare earth ions were introduced into the tungsten/molybdate host,and the structure as well as photoluminescence properties of the prepared samples were systematically studied,providing a basis and support for the research and development of tungsten/molybdate phosphors for WLEDs that can be effectively excited by UV/NUV light.The main research contents are as follows:（1）A series of NaBi（WO₄）₂:Eu³⁺,Na Bi（WO₄）₂:Dy³⁺,Eu³⁺and Na Bi（Mo O₄）₂:Sm³⁺phosphors were synthesized by the solid-state reaction method.For the Na Bi（WO₄）₂:0.8Eu³⁺sample doped with the optimal Eu³⁺ion concentration,the low symmetry of the lattice sites occupied by Eu³⁺ions was confirmed using Judd-Ofelt theory,and the temperature dependence of the emission intensity indicated excellent thermal stability and it is closer to the standard red light than the commercial red Y₂O₂S:Eu³⁺phosphor.For Na Bi（WO₄）₂:Dy³⁺,Eu³⁺phosphor,fixing the optimal concentration（8 mol%）of Dy³⁺ions and changing the concentration of Eu³⁺ions,the color coordinates of the samples can move from yellow-green to orange light region through the energy transfer of Dy³⁺→Eu³⁺ions,and the energy transfer mechanism is dipole-dipole interaction.The variable temperature emission spectra showed that the Na Bi（WO₄）₂:Dy³⁺,Eu³⁺phosphors have good thermal stability.For the Sm³⁺ion single-doped Na Bi（Mo O₄）₂phosphors,the effect of Sm³⁺ion doping concentration on the photoluminescence performance of the sample and the concentration quenching mechanism were discussed in detail,the results of CIE coordinates and correlated color temperatures indicated that the Na Bi（Mo O₄）₂:Sm³⁺samples were expected to be used as an orange-red light components in near-UV excited WLEDs.（2）Two new scheelite structured NaCaGd（WO₄）₃:Tb³⁺,Eu³⁺and KSr La（Mo O₄）₃:Tm³⁺,Dy³⁺phosphors were designed and synthesized by the cationic equivalence substitution strategy.Eu³⁺ions were introduced into the Na Ca Gd（WO₄）₃:0.6Tb³⁺sample doped with optimal Tb³⁺ion concentration,and the energy transfer of Tb³⁺→Eu³⁺ions can achieve a wide range of light color tunability from green to red light of the sample with an energy transfer efficiency of 96.36%,and it was confirmed that the energy transfer mechanism was dipole-dipole interaction.Its application potential was evaluated by testing the variable temperature emission spectra of the representative sample as well as the photoluminescence performance of as-fabricated WLED device.The effect of Tm³⁺and Dy³⁺ion doping concentration on their photoluminescence properties in KSr La（Mo O₄）₃samples was also investigated.The luminescence color of samples remained in the cool white region by fixing the Tm³⁺ion concentration（6 mol%）and changing the Dy³⁺ion concentration.By introducing Tm³⁺ions into the KSr La（Mo O₄）₃:0.06Dy³⁺phosphor,the luminescence color of the sample can be shifted from yellow to blue-white region via white light,and its excellent thermal quenching resistance indicated that the synthesized sample had good potential for the application in warm white emitting phosphors with single substrate.（3）A series of Sm³⁺,Eu³⁺and Pr³⁺ions single-doped Ba₂Mg WO₆phosphors with double perovskite structure were prepared by high-temperature solid-phase method.Under the excitation of charge transfer band,the effects of doping concentration on the photoluminescence properties of the samples and the symmetry of the lattice sites occupied by rare earth ions were investigated in detail.The effects of charge compensator A⁺on the structure,photoluminescence performance and fluorescence decay times of Ba₂Mg WO₆:Eu³⁺,A⁺（A⁺=Li⁺,Na⁺,K⁺）phosphors were studied and analyzed,and the results showed that the introduction of A⁺could prevent the formation of vacancy defects in the host,thus effectively improving the emission intensities and fluorescence decay times of the samples,the introduction of Li⁺ions could effectively improve the thermal stability of Ba₂Mg WO₆:Eu³⁺phosphor.The effects of various W/Mo ratios on the structure and photoluminescence performance of Ba₂Mg WO₆:Eu³⁺,Li⁺phosphors were studied and discussed.With the increase of Mo content,the maximum excitation wavelength of the charge transfer band shifted from 319 nm to 397 nm,and when the Mo content was 0.6,the corresponding sample had the best photoluminescence performance under the excitation of 397 nm,which makes it a potential application in the field of NUV excited WLEDs.