Synthesis And Luminescence Properties Of Rare Earth (Eu²⁺,Ce³⁺) Doped Sr₂Si₅N₈ Phosphors

Based on its advantages such as environmental protection,long life,white light emitting diodes（LEDs）is expected to become a new generation of lighting source.As an important part of white LEDs,phosphors have great influence on the color,brightness and life.In the phosphor systems,silicon-based nitride phosphors exhibit a long-wavelength emission band in the range of visible light range due to the tetrahedral network structure of Si-N in the crystal structure and the excitation from near ultraviolet to blue light（370 nm-465 nm）,which can be well applied in white LEDs.In this thesis,Sr₂Si₅N₈:Eu²⁺and Sr₂Si₅N₈:Ce³⁺phosphors were synthesized by carbothermal reduction-nitridation method.The effects of rare earth ions(Eu²⁺,Ce³⁺)doping and partial substitution of Sr²⁺and Si⁴⁺with Y³⁺,Al³⁺and Ti⁴⁺on the structure and luminescent properties of the phosphors were investigated.The research results are shown as follows:（1）Sr₂Si₅N₈:Ce³⁺phosphors were successfully synthesized at 1500℃.XRD spectra showed the crystal structure of the sample is consistent with Sr₂Si₅N₈ standard phase（PDF 85-0101）and belongs to the orthogonal crystal system（Pmn2₁ space group）.At 510 nm wavelength detection,the spectrum was at 300 nm-500 nm,and under the excitation of 430 nm,Sr₂Si₅N₈:Ce³⁺phosphors exhibit strong broad-peak emission in the range of 450 nm-650 nm,with a peak of about 510 nm,which originates from the 5d→4f electron transition of Ce³⁺.With the increase of Ce³⁺doping content,the luminescence intensity of phosphors first increases and then decreases,and concentration quenching occurs when the Ce³⁺doping concentration exceeds 3%.Finally,the effect of charge compensation of alkali metal ions Li⁺,Na⁺and K⁺on luminescence property of Sr₂Si₅N₈:0.03Ce³⁺phosphors by was investigated.With 3%Li⁺,3%Na⁺and 4%K⁺co-doping,the optimal luminescence intensity of the samples were obtained,which is 33%,25%and 14%higher than that of Sr₂Si₅N₈:0.03Ce³⁺,respectively（2）Sr₂Si₅N₈:Eu²⁺phosphors were successfully synthesized in thesis.XRD patterns showed that the diffraction peaks of the samples corresponded well to the standard diffraction peaks of Sr₂Si₅N₈ structure（PDF 85-0101）one by one,and there was no impurity peaks.At 613 nm emission wavelength detection,the excitation spectrum is at 300 nm-550 nm,from the 4f⁷→4f⁶5d¹ transition of Eu²⁺,and under the excitation of 450 nm,the emission spectra show a band emission between 500 nm and750 nm with a peak at 613 nm,which corrponding to the 4f⁶5d¹→4f⁷ transition of Eu²⁺.With the increase of Eu²⁺doping amount,the luminescence intensity first increases and then decreases,and reaches the maximum when the doping concentration is 2%.The photoluminscence spectra of Sr₂Si_5-xAl_xN₈:0.02Eu²⁺(Sr_2-xY_xSi_5-xAl_xN₈:0.02Eu²⁺)phosphors show that the luminescence intensity first increases and then decreases with the increase of doping concentration of Al³⁺(or Y³⁺and Al³⁺),and the luminescence intensity is the strongest when doping concentration are 0.4（or 0.16）,respectively,which is 22%higher than that of Sr₂Si₅N₈:0.02Eu²⁺phosphors.Lastly,Ce³⁺co-doping improves its luminescent properties of Sr₂Si₅N₈:0.02Eu²⁺phosphor.When the doping amount is 0.03,the luminescent intensity of the phosphor is the highest,which is 66%higher than that without co-doping.（3）Sr₂Si₅N₈:0.02Eu²⁺phosphors were synthesized with using glucose(C₆H₁₂O₆)as reducing agent.The optimum temperature is 1500℃and doping amount of reductant n(C₆H₁₂O₆)/n（SrCO₃）=1.5 were determined,than the carbon powder as reducing agent sample luminous intensity could be improved by 34%.XRD results showed that the diffraction peak of the sample was consistent with the standard diffraction peak of Sr₂Si₅N₈ structure（PDF 85-0101）.And the luminescence spectra show that the luminescence intensity increases first and then decreases with the increase of Ti⁴⁺doping content.When the doping content is 0.12,the excellent luminescence performance can be obtained,specifically,the luminescence intensity is increased by 54%,and the lifetime is extended to 5.37 ms.