Synthesis And Photoluminescence Properties Of Si-Al-O-N Materials

In recent years phosphors for white light-emitting diodes(LEDs), which can be excited by UV-visible,were investigated extensively. Rare-earth(RE)-activated Si-Al-O-N luminescent materials have attracted much attention due to their excellent thermal and chemical stabilities,novel luminescence properties,and potential applications as phosphors.In this article,the phosphor SiAlON:RE and Mullite:RE were synthesized by solid-state reaction and sol-gel reduction-nitridation processing,respectively.The influences of variety and concentration of activator,sensitizer,complexing agent on sol-gel processing and calcined temperatures on luminescent properties were discussed.Phase composition and structure were investigated by XRD;the luminescent properties of the phosphors were detected and discussed by using phosphor luminometer(PL);the molecular structure of SiAlON precursor and the reaction process was analyzed by the IR and TG-DTA, respectively.The experimental results indicated that:1.β-SiAlON phosphor was synthesized from Si,AlN,SiO₂ and rare earth oxide powders by solid-state reaction.The luminescence of Eu,Ce, Sm mon-dopedβ-SiAlON phosphors were strong blue,light blue and weak wine excited by UV,respectively;the Eu,Tb co-dopedβ-SiAlON phosphors shown blue and green luminescence at different temperature; the Eu,Mn co-doped sample shown green luminescence under UV.2.Theβ-SiAlON:Eu²⁺ shown two broad bands in the excitation spectrum centered at 285nm and 325nm,and a blue emission band centered at about 485nm with a full-width at half-maximum(FWHM) of 75nm,which correspond to 5d-4f transition of Eu²⁺.The critical concentration of Eu²⁺ inβ-SiAlON host was 8%.The excitation and emission spectrum of Eu²⁺,Tb³⁺ co-dopedβ-SiAlON under 1650℃calcination shifted to 470nm and 540nm,respectively;the excitation spectrum of Eu²⁺ was split into 3 peaks,the crystal field splitting is～17000cm^-1,which attributed to the incorporation of Tb³⁺.The mechanism analysis shown that the Eu²⁺ ions were coordinated on empty spheres which were formed by a continuous channel along[001]direction inβ-SiAlON.3.β-SiAlON:Eu²⁺ phosphor was synthesized by the sol-gel reduction-nitridation process.The SiAlON precursor using citric acid as complexing agent was calcinated at 1450～1600℃,and the luminescence of samples were green and blue,respectively;the PL intensity enhanced when calcinations temperature increased;excess carbon concentration was harmful for the luminescence. 4.Mullite phosphor was prepared by solid-state reaction.The luminescence of Eu,Ce,Tb doped mullite phosphors were dark blue, light blue and weak white excited by UV,respectively;the Eu,Tb co-doped mullite phosphors shown bright green luminescence excited by UV and the Eu,Mn co-doped sample shown weak red luminescence under UV.5.The observed strong enhancement of the Tb³⁺ emission for introducing Eu²⁺ content is attributed to the energy transfer effect from Eu²⁺ to Tb³⁺.According to the Dexter's energy transfer formula of multipolar interaction,the energy transfer between Eu²⁺ and Tb³⁺ is due to the electric dipole-dipole interaction of the resonance transfer.The optimum proportion of Eu,Tb co-doped 3/2-mullite is found to be 3Al₂O₃-2SiO₂:0.05Eu,0.05Tb.