Preparation And Luminescence Properties Of Single-Phased Na₂Ca₃Si₂O₈ Phosphor

White light emitting diode?LED?,known as the green light source inthe 21st century,is the“new hope”of solid state lighting source due to its high efficiency,strong applicability,short response time,no pollution to the environment and low working voltage.At present,the white LED has been marketed,but the most widely used combination is YAG:Ce³⁺and InGaN chips.However,the lack of red light component leads to the disadvantages of high color temperature?CCT>4500K?and low color rendering index?CRI<80?,which inevitably limit its application in indoor lighting or backlighting.What can be remedied is that this disadvantage can be recovered by adding appropriate red phosphors,for which a great deal of research has been devoted to the application of white LED,a new type of red luminescent material.However,there is a serious problem of reabsorption in mixed phosphors,a single white LED phosphor need to be developed.On the other hand,silicate luminescent materials have the advantages of good chemical stability,long term bombardment resistance,excellent crystallinity and transmittance due to the close binding between their ions,easily-obtained SiO₂ raw materials of high purity.It is cheap and suitable for mass production,which thus has always been a hot topic in the research of luminescent materials.In this paper,a single substrate Na₂Ca₃Si₂O₈?NCSO?phosphor forwhite LED excited by ultraviolet/near ultraviolet light was synthesized by traditional high temperature solid state method.The phase,luminescence and energy transfer of phosphors were studied by means of characterization with different concentrations and different rare earth ions.The details follows:?1?The Na₂Ca₃Si₂O₈ matrix material was synthesized at differenttemperatures.It was proved that 1200^oC is the proper temperature for the synthesis of Na₂Ca₃Si₂O₈ matrix material.According to diffuse reflectance spectroscopy,the energy band gap of the matrix material is 3.621eV,and the particle size of the matrix material is estimated to be 5.53?m by scanning electron microscope,which proves that the matrix is suitable for use as phosphor material.?2?Na₂Ca₃Si₂O₈:Tb³⁺phosphors were synthesized in CO reduction byhigh temperature solid state method?HTSSM?.The XRD diffraction peaks of the sample sintered at 1200^oC for 5h were identical with the standard card23-668 of Na₂Ca₃Si₂O₈.It proved that the samples have single phase.It can be seen that the PLE spectra monitored at 544nm show a strong sharp absorption at250nm and weaker band ranged from 300 to 500nm corresponding to 4f?4f electron transition absorption.Under the excitation at 250nm,the emission spectrum shows four sharp emission peaks,among which the peak value of544nm?⁵D₄?⁷F₅?is highest,and the sample exhibits excellent green light.The luminescent intensity is getting stronger with the concentration of Tb³⁺increasing.In other words,this phenomenon indicates that the sample has no obvious concentration quenching.?3?Na₂Ca₃Si₂O₈:Sm³⁺red phosphor was synthesized by HTSSM.Noadditional XRD peaks are found,which indicates single phase of phosphor.The samples have four strong narrow band emission spectra between 550-750nm,among which the highest is at 601nm,and the excitation spectrum 325-500nm has six obvious excitation peaks,the highest is 404nm.By doping different concentrations of Sm³⁺,the emission spectrum intensity of phosphor increases and then decreases.It reaches the maximum at x=0.01.The Dexter theory proves that the electric dipole-dipole interaction results in the concentration quenching of Sm³⁺.According to the color coordinate analysis,the color of the phosphor is basically kept in?0.609,0.390?indicating that it has good color stability.?4?Na₂Ca₃Si₂O₈:Tb³⁺,Sm³⁺phosphors were synthesized by theHTSSM.Under the excitation at 250nm,the Tb³⁺and Sm³⁺doped phosphors show strong blue green and orange red light respectively,so that the color of phosphors can be changed by changing the doping concentration of Sm³⁺ions.Finally,when the concentration of Sm³⁺ions reaches 0.06mol,the sample is warm white.At the same time,the interaction between Tb³⁺and Sm³⁺ions has been found and proved,and the energy transfer has been demonstrated mainly through the electric dipole–dipole interaction.?5?Na₂Ca₃Si₂O₈:Tb³⁺,Eu³⁺phosphors were synthesized by theHTSSM in the atmosphere of CO reduction.The luminescence characteristics of phosphors are analyzed in detail.Under the UV excitation at 350nm,the phosphors exhibit strong blue green light and red light by doping Tb³⁺and Eu³⁺,respectively.And the color of phosphors could be changed by the doping concentration of Eu³⁺ions.By the way,the interaction between Tb³⁺and Eu³⁺ions is found and proved,and the energy transfer mainly through exchange interaction is explained by calculation.The strong absorption of the Na₂Ca₃Si₂O₈:Tb³⁺,Sm³⁺,Na₂Ca₃Si₂O₈:Tb³⁺,Eu³⁺phosphors in the range of 250-380 nm suggests that they have great potential for WLED.