【作者】 罗海滨；

【导师】 洪樟连；

【作者基本信息】 浙江大学 ， 材料学， 2010， 硕士

【摘要】 白光LED有着节能环保、高效安全、坚固可靠等优点,是未来的新一代光源,蕴藏着巨大的经济效益和社会效益。随着（近）紫外LED芯片技术不断发展,开发探索新型的可在近紫外光有效激发的LED用三基色荧光粉具有重要的研究意义和实用价值。本论文在总结白光LED用三基色荧光粉的研究现状的基础上,基于硅酸盐体系荧光粉具有较稳定的热性质和化学性质,对新型Ba₂Si₃O₈:Eu²⁺荧光粉的合成和性能进行了研究。采用高温固相法和溶胶-凝胶法两种制备工艺合成了绿色荧光粉Ba₂Si₃O₈:Eu²⁺,比较了两种制备工艺对荧光粉形貌和性能的影响,并在此基础上采用Pechini溶胶-凝胶法制备了核-壳结构的SiO₂@Ba₂Si₃O₈:Eu²⁺荧光粉。利用DTA、TG、XRD、SEM、TEM、PL等测试技术,对Ba₂Si₃O₈:Eu²⁺体系荧光粉的物相形成过程、颗粒形貌、发光性能等各方面进行了研究。本研究第一部分内容是采用高温固相法合成了新型绿色荧光粉Ba₂Si₃O₈:Eu²⁺。研究发现,混合料在升温过程中经历了BaSiO₃→Ba₂Si₃O₈的物相演变过程;荧光粉样品激发光谱系覆盖300nm～450nm的连续宽带谱,谱峰中心位置在370nm左右,可与（近）紫外LED芯片相匹配;发射光谱中心峰位在502nm左右,属于典型的Eu²⁺离子4f⁶5d¹-4f⁷跃迁,为强烈的绿色发光。结果表明,烧成温度、保温时间、助熔剂浓度、激活剂浓度等合成工艺参数对荧光粉的物相结构、颗粒形貌和发光性能都有很大影响。研究获得了适宜的荧光粉制备工艺条件为:烧成温度为1250℃、保温时间为3h、助熔剂H₃BO₃含量为5wt%。改变激活剂浓度的研究表明:该体系激活剂的临界猝灭浓度约为Eu=0.05,浓度猝灭机制应为偶极-偶极相互作用。此外,还采用固相合成工艺,研究了Ca²⁺、Sr²⁺碱土金属固溶取代基质中Ba²⁺后对荧光粉性能的影响。研究发现,少量Ca²⁺取代基质Ba²⁺离子,会增强样品的发光强度;不过,过多引入Ca²⁺会生成杂相并降低荧光粉的发光强度。此外发现:Ca²⁺取代后样品的发射光谱发生了一定的蓝移;而Sr²⁺取代则会使发射光谱发生红移,持续降低样品的发光强度。还有,通过引入Ce³⁺研究了它对激活剂Eu²⁺发光的敏化作用。结果表明,通过Ce³⁺共掺可大幅增强荧光粉的发光强度,Ce³⁺与Eu²⁺之间存在能量传递过程,Ce³⁺的最佳共掺浓度为0.04,可使荧光粉的强度增强到单掺Eu²⁺的荧光粉的8.64倍,Ce³⁺离子具有显著的敏化发光作用。其次,采用溶胶凝胶法制备了Ba₂Si₃O₈:Eu²⁺荧光粉。结果发现,溶胶-凝胶工艺中,随着热处理温度的提高,样品中依次发生了从Ba₂SiO₄→BaSiO₃→Ba₂Si₃O₈的物相演变过程。最终制备的荧光粉激发光谱为覆盖300nm-450nm,峰位中心在370nm左右的连续宽带谱,可被（近）紫外LED芯片激发。对应的发射谱为峰值在502 nm左右的带状谱,是典型的Eu²⁺离子4f⁶5d¹-4f⁷跃迁,发出绿光。虽然通过溶胶-凝胶法制备的荧光粉样品可避免球磨工艺,可直接获得分散性较好的、颗粒尺寸为2～4μm的荧光粉颗粒,颗粒尺寸比固相法要小得多,可有效降低荧光粉的颗粒尺寸。不过,与大多数研究结果类似,本研究中通过溶胶-凝胶法制备的荧光粉样品发光强度比高温固相法制备样品要弱。此外,本研究还利用Pechini溶胶-凝胶法,以尺寸可控的、成本较低的球形SiO₂颗粒为核,成功合成了以Ba₂Si₃O₈:Eu²⁺荧光粉为壳层的核-壳结构材料。XRD、SEM、TEM等测试结果表明,Ba₂Si₃O₈:Eu²⁺荧光粉成功包覆在球形SiO₂颗粒表面,且产物保持了良好的球形结构特征,具有良好的分散性,颗粒尺寸在330nm左右。光谱测试结果表明,核-壳结构SiO₂@Ba₂Si₃O₈:Eu²⁺荧光粉的激发光谱为覆盖300nm-450nm,峰位中心在370nm左右的连续宽带谱,可被（近）紫外LED芯片激发。而发射谱为峰值位于502 nm左右的带状谱,是典型的Eu²⁺离子4f⁶5d¹-4f⁷跃迁,发出绿光。研究表明,增加包覆次数可有效增强材料的发光强度。更多还原

【Abstract】 White light-emitting diodes have been considered as the next generation light source because of their advantages such as energy-conservation,environmental protection,high-efficiency and reliability,which provides tremendous economic and social benefits.With the continuous development of near-UV-LED chip technology,it has important research significance and application value to explore novel trichromatic phosphor which can be excited effectively by near ultraviolet LED.In this thesis,research progress of trichromatic phosphor for white LED was summarized.Based on the thermal properties stability and chemical properties stability of the silicate matrix,a novel green phosphor Ba₂Si₃O₈:Eu²⁺ was succussfully synthesized by solid-state reaction and sol-gel method.The formation process, microscopic structure,luminescence properties of the phosphors were studied by DTA, TG,XRD,SEM,TEM,PL measurement,etc.The morphology and luminescent properties of phosphor synthesized by two different technique routes were compared. Furthermore,the morphology of the phosphor was designed with the core-shell structure phosphor SiO₂@Ba₂Si₃O₈:Eu²⁺,whish was synthesized by Pechini sol-gel method followed by post-annealing process using mono-dispersive SiO₂ microspheres as cores and Ba₂Si₃O₈:Eu²⁺ as shells.A novel green phosphor Ba₂Si₃O₈:Eu²⁺ was successfully synthesized by solid-state reaction.With the increase of calcining tempereture,the sample has experienced the phase evolution process from BaSiO₃→Ba₂Si₃O₅.The excitation spectrum of product Ba₂Si₃O₈:Eu²⁺ phosphor is a broad band covered 300nm～450nm with peak center around 370nm,which well-matched with the emission of near-UV-LED chips.On the other hand,the emission spectrum is a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission spectral band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transitioncenter.It was revealed that the preparation parameters for phosphors such as calcine temperature,reaction time,flux concentration,activator concentration have great impact on morphologies and luminescent properties of as-prepared phosphors.The optimized parameters for present phosphors were determined as follows:calcine temperature of 1250℃,holding time of 3h,flux concentration of 5wt%and activator concentration of Eu ions be 0.05.The concentration quenching mechanism of Eu ions was supposed to be the dipole-dipole interaction.In the solid-solution matrix of alkaline-earth metal such as Ca²⁺ and Sr²⁺ ions replaced Ba²⁺ in the lattice,the luminescence properties change too.It was found that the Ca²⁺ replacement makes blue-shift in the emission peak and a little amount of Ca²⁺ replacement for Ba²⁺ enhances the emission intensity while access amount of Ca²⁺ replacement reduces the emission intensity.On the contrary,the Sr²⁺ replacement reduces the emission intensity and causes red-shift within the doping level. Furthermore,the sensitization effect of Ce³⁺ ions has been verified and the luminescence intensity of Eu²⁺ emission could significantly enhanced by Ce³⁺ co-doping.The energy transfer process between Ce³⁺ and Eu²⁺ was observed and the optimized concentration of Ce³⁺ ions is 0.04,which could increase the luminescence intensity for almost 8.6 times as much as that of Ce³⁺-free Ba₂Si₃O₈:Eu²⁺ phosphor.It was revealed that the phase evolution process is Ba₂SiO₄→BaSiO₃→Ba₂Si₃O₈ with increasing temperature for sol-gel derived samples.The excitation spectra of the prepared phosphor covers 300nm～450nm with peak center at 370nm,which matches well with the emission spectrum of near-UV-LED chips.The emission spectrum consists of a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission spectral band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transition center.Well dispersed phosphor with average particle size around 2～4μm could be obtained by sol-gel method with merits of ball milling process free.However,it was found that the luminescence intensity of sol-gel derived phosphor is weaker than that of solid-state reaction derived phosphor.Core-shell structure phosphor SiO₂@Ba₂Si₃O₈:Eu²⁺ was successfully synthesized by Pechini sol-gel method using size-controllable,low-cost SiO₂ microspheres as cores and Ba₂Si₃O₈:Eu²⁺ phosphor as shells.The XRD,SEM,TEM results indicated that Ba₂Si₃O₈:Eu²⁺ phosphor could be successfully coated on the surface of SiO₂ microspheres.The obtained core-shell structure SiO₂@Ba₂Si₃O₈:Eu²⁺ phosphor has good dispersion state and maintains spherical structural features with particle sizes around 330nm.The phosphor shows broad band covered 300nm～450nm with peak center around 370nm,which matches well with the emission of near-UV-LED chips. Its emission spectrum consisted of a single intense broad band centered at 502nm and exhibits intensity green light.The broad emission band could be attributed to the Eu²⁺ activator with classical 4f⁶5d¹-4f⁷ parity allowed transition center.Furthermore,the luminescence intensity of SiO₂@Ba₂Si₃O₈:Eu²⁺ phosphor could be enhanced by increasing the numbers of coated times.更多还原