Synthesis And Luminescent Properties Of Eu³⁺-Doped Lanthanum Cerium Composite Oxides Modified With Various Surfactants

In recent years,the new rare-earth oxides as inorganic luminescent nanomaterials have been widely used in diverse fields.Cerium dioxide with cubic fluorite structure is a typical rare-earth oxide.It has been widely used in fuel cells,electrolytic,catalytic and luminescent fields due to its unique electrical,optical,catalytic and mechanical properties.Nevertheless,there are few reports on the rare-earth doped cerium and lanthanum composite,especially in the aspect of light emission.In this paper,the La₂Ce₂O₇ composite and rare-earth Eu³⁺was used as substrate and activator,respectively.The effects of different surfactants on their structure,morphology and luminescence properties were investigated in detail.Here,the rare-earth Eu³⁺-doped La₂Ce₂O₇:xEu³⁺?x=0.0⁰.9?composite oxide was synthesized by hydrothermal self-rising method.Assisted with different surfactants?glycine,polyvinyl alcohol,sodium dodecyl sulfate,and cetyl trimethyl ammonium bromide,respectively?and a subsequent heat treatment process,the phosphor nanopowders were finally obtained.The X-ray diffraction,Raman spectroscopy,photoluminescence,fluorescence decay curves,particle size distribution,color coordinates and scanning electron microscopy were used to characterize the effect of the surfactants on the structure,particle size,surface morphology and luminescent properties.The results showed that the structure of the sample without surfactant was a mixture of La₂O₃ and CeO₂ oxides.After the four surfactants modification,the La₂Ce₂O₇:xEu³⁺?x=0.0⁰.9?solid solution with cubic fluorite structure was successfully synthesized,and the doping of Eu³⁺had little influence on the structure.The photoluminescence analysis indicateed that the dominant excitation wavelength of the sample belonged to the characteristic transition of⁷F₀?⁵D₂ of Eu³⁺at 466 nm in the blue light region.Applied the blue light 466 nm as the excitation wavelength,the emission spectra were achieved,and the predominant emission was the⁵D₀?⁷F₂ electric dipole transition of Eu³⁺at613 nm.The optimal luminescence intensity was determined when the doping concentration of Eu³⁺was 0.7.Moreover,the fluorescence intensity of the surfactant-modified composite samples was significantly higher than that of the surfactant-free samples and the CeO₂:Eu with the corresponding surfactant.Among them,the glycine-modified sample displayed the highest fluorescence intensity.After modification with surfactants,the irregular circular or elliptical shape with severe agglomeration of the samples was obviously improved to a more regular spherical shape with uniform size and good distribution.Applying the glycine-modified sample powders to coat on a commercial blue GaN LED chip,the strong red light was generated under blue light irradiation as the power was on.Therefore,the Eu³⁺-activated La₂Ce₂O₇ composite samples modified with surfactants are expected to have greater application potential in solid-state lighting and optoelectronic devices.