Spectrum Tuning Of Rare Earth Doped Silicate Phosphors By Ion Substitution

LEDs have been widely used in the field of lighting and display owing to their long lifetime,energy saving qualities,high luminous efficiency,and environmentally friendly character.In the future,the demand in this market will increase.At the same time,with the progress of energy conservation and emission reduction,many countries and regions have relevant policies to promote the development of LED.LED lighting technology has made continuous progress and new application field is emerging.At present,the vigorous construction of"smart cities"around the world also promotes the development of LED lighting technology.In this paper,three kinds of silicate phosphors have been successfully prepared by the traditional high-temperature solid-state method:Sr_0.84Na_0.03Al_1.69Si_2.29O₈:Eu^2+,K_1-xLa_0.99-xSi O₄:0.01Eu²⁺/Eu³⁺,x(Mg²⁺,Sr²⁺)and Na₂Ba_5.99-xSi₂O₇Si_2-xO8:0.01Eu²⁺,x(Y³⁺,Al³⁺).The crystal structure and luminescence properties of these three silicate phosphors were studied,and the mechanism of some phenomena was discussed.In the first chapter,the development of phosphor materials,white LEDs,common testing and characterization methods for phosphor materials,spectral tuning approaches in pc-WLED phosphors,the status and development prospects of phosphors are introduced.This chapter provides relevant theoretical basis for the research.The second chapter of this thesis mainly introduces the raw material reagents,related instruments and experimental process used in the preparation and characterization of phosphor samples.In the third chapter,the structure and optical properties of a series of Eu²⁺-activated Sr_0.84Na_0.03Al_1.69Si_2.29O₈ phosphors prepared by high temperature solid-state method were studied.The XRD test showed that the prepared sample was the target phosphor of Sr_0.84Na_0.03Al_1.69Si_2.29O₈:Eu²⁺with pure phase.At 312 nm excitation,this phosphor can emit broad blue light in the range of 380 to 500 nm and the peak at 404 nm.The optimum doping concentration of Eu²⁺ions is x=0.02.The mechanism of concentration quenching was confirmed to the dipole-dipole interaction mechanism.Sr_0.84Na_0.03Al_1.69Si_2.29O₈:Eu²⁺phosphor has excellent thermal stability,and the emission intensity can still reach 95.6%of the initial value（luminous intensity at 25°C）at 150°C.The thermal stability is better than commercial BAM blue phosphor(BaMgAl₁₀O₁₇:Eu²⁺).The activation energy Ea of Sr_0.83Na_0.03Al_1.69Si_2.29O₈:0.01Eu²⁺is calculated as 0.33 eV,which can also prove that it has good thermal stability.In addition,Sr_0.84Na_0.03Al_1.69Si_2.29O₈:Eu²⁺phosphor shows excellent color stability.All the results imply that Sr_0.84Na_0.03Al_1.69Si_2.29O₈:Eu²⁺phosphor is a potential blue phosphor for LED.The fourth chapter mainly introduces the luminescence properties and spectral changes of K_1-x-x La_0.99-xSiO₄:0.01Eu²⁺/Eu³⁺,x(Mg²⁺,Sr²⁺)（x=0.02,0.04,0.06,0.08,0.10）,which are prepared by a high-temperature solid-state method in a reducing atmosphere at 1050°C.The XRD test shows that the prepared sample is the target phosphor.The samples are pure and there is no obvious impurity.When KLaSiO4:Eu³⁺is synthesized under the air condition,it emits red light which originates from the characteristic emission of Eu³⁺.But when it is prepared in the reducing conditions,it emits blue light.This is because the sample contains a little amount of Eu²⁺.As（K+,La3+）were substituted by(Mg²⁺,Sr²⁺)gradually,the spectra changed obviously.There appeared an obvious green broad peak in the emission spectrum which was attributed to the emission of Eu²⁺.The green emission intensity first rise then descend.The light color of the sample also changes from blue to green.By doping(Mg²⁺,Sr²⁺)ions,the photoluminescence performances of K_1-xLa_0.99-xSi O₄:0.01Eu²⁺/Eu³⁺,0.04(Mg²⁺,Sr²⁺)phosphors has been improved.However,the thermal stability of the phosphor needs to be further improved.The fifth chapter mainly introduces the luminescence properties and spectral changes of Na₂Ba_5.99-xSi₂O₇Si_2-xO₈:0.01Eu²⁺,x(Y³⁺,Al³⁺)（x=0,0.4,0.8,1.2,1.6,2.0）phosphors.The XRD pattern shows that these samples are the target phosphor,and there is no obvious impurity until x exceeds 1.2.When x=0,Na₂Ba_5.99Si₂O₇Si₂O₈:0.01Eu²⁺have two emission peaks,respectively 443 nm(blue-light Ba²⁺site)and500nm(green-light Ba²⁺site).Under ultraviolet light,the sample emits blue-green light.In this experiment,Y³⁺is used to replace Ba²⁺,and Al³⁺is used to replace Si⁴⁺.With the gradual increase of the concentration of substituted ions(Y³⁺,Al³⁺),the peak at 443 nm in the spectrum gradually decreases and disappears,while the emission intensity of the peak at 500 nm increases first and then decreases.This phenomenon can also indicate that in the Na₂Ba₆Si₂O₇Si₂O₈ matrix,the doped Y³⁺preferentially occupies the blue-light Ba²⁺site.The CIE coordinates of the sample also move from the blue area to the green area.By doping(Mg²⁺,Sr²⁺)ions,the luminescent color and luminous intensity of the sample has been changed and the emission spectrum of the phosphor has a single emission peak.However,the entirety thermal stability of the phosphor has not been significantly changed.