Study On Synthesis And Properties Of Luminescent Materials La₂O₃: Sm³⁺by Combustion Method

Light-emitting diode?LED?has excellent properties,such as long life?5000-10000 hours?,small volume,low consumption and low pollution.As is known to all,a method of preparation of white LED has been using the blue LED combined with yellow phosphors.However,this method makes the color rendering index of LED and luminous efficiency low due to lack of red component.Another method has been using to produce white LED with better color rendering index,ie.,using tricolor phosphors?red,green and blue phosphors?with near ultraviolet?370-420 nm?chip.Therefore,the tricolor phosphors which can be excitated by near-ultraviolet were widely research.Among them,red phosphors are crucial.On the one hand,as one kind of rare earth ions with the activator of luminescent materials,Sm³⁺ ions are studied at present.The 4f-4f absorption transition of Sm³⁺is near ultraviolet region and has been little influenced around the crystal field which is able to absorb the energy and emit high purity red light.For suitable host materials,Sm³⁺ can effectively absorb the near ultraviolet light?350-450 nm?,which meet the preparation requirements of LED phosphors.Therefore,Sm³⁺ ions are used as activate ions in lots of rare earth luminescent materials.On the other hand,the host materials play a key role in which affects the properties of phosphors.Among these rare earth oxides,due to its easiness to synthesis,simple structure with low phonon frequency,La₂O₃ doped with rare earth ions for phosphors has been widely investigated.1.Nanomaterial La₂O₃:Sm³⁺ was prepared by combustion synthesis.The morphology and structure were characterized and analyzed by X-ray diffraction?XRD??Scanning electron microscope?SEM?and High resolution transmission electron microscopy?HRTEM?.The luminescent properties were also investigated by fluorescence spectrum meanwhile the decay time was tested and depicted the CIE chromatograms.The results showed:The sample material was hexagonal structure;The grain size was approximately 34 nm;Under the 411 nm excitation,the major emission peaks were observed at ⁴G_5/2?⁶H_5/2?568 nm?,⁴G_5/2?⁶H_7/2?611 nm,the highest intensity?and ⁴G_5/2?⁶H_9/2?654 nm?.The decay lifetime was about 202 us;The chromaticity coordinate was approximately?0.5849,0.4143?which is located in the reddish-orange area.2.Combustion synthesis was used to prepare the same annealing temperature?annealing at 1000 ??with different doped concentration of Sm³⁺?x=1,1.5,2,3 and 5 mol%?of nanomaterials La₂O₃:xSm³⁺ and the same doped concentration?1.5 mol%?with different annealing temperature?annealing at 400,600,800 and 1000 ? for 1 hour?of nanomaterial La₂O₃:Sm³⁺ The morphology,structure and particle size were characterized by X-ray diffraction?XRD?and Scanning electron microscope?SEM?.The luminescent properties were also investigated by fluorescence spectrum and depicted the CIE chromatograms.The results showed:As the concentration of doped Sm³⁺ ions increased,the emission intensity of La₂O₃:Sm³⁺ were up to its maximum.When the concentration of doped Sm³⁺ ions was 1.5 mol%and the concentration quenching effect was observed from the main dipole-dipole interaction.With the increased of annealing temperature,the average grain size and the emission intensity of La₂O₃:Sm³⁺ increased.