【作者】 沈常宇；

【导师】 冯华君； 金尚忠；

【作者基本信息】 浙江大学 ， 光学工程， 2009， 博士

【摘要】 白光LED被称为第四代光源,与当今普遍使用的白炽灯、荧光灯光源相比,其具有寿命长、功耗低、响应快、尺寸小、抗冲击性好和无汞污染等优势,可以满足人们对安全、节能、环保、舒适、美观等多方面要求。目前使用最广泛、技术最成熟的白光LED技术是蓝光芯片加YAG黄色荧光粉技术,它是用蓝光LED芯片发出蓝光,然后去激发YAG荧光粉产生黄光,剩余的蓝光与黄光混合形成白光。但是YAG黄色荧光粉存在发射光谱的宽度不够宽,缺少红光成分的固有缺陷。因此该种类型白光LED色温偏高、显色指数偏低,难以达到普通照明要求。改善现有YAG荧光粉或寻找发射光谱较宽的替代YAG的其它荧光粉以提高白光LED的显色性对于当前固体照明显得尤为重要。高温固相法是合成稀土掺杂荧光材料传统的和应用最多的方法,其制备方法简单,只要控制好温度和焙烧时间,样品成功率高;微波辐照法是80年代中期迅速发展起来的新兴荧光材料合成方法,具有快速、高效、受热均匀等特点。本文采用微波辐照法和高温固相法相结合,充分利用高温固相法和微波辐照法的优点,制备出了一系列的白光LED用荧光粉。研究了Ba²⁺共掺Sr₃SiO₅:Ce³⁺,Li⁺橙黄色荧光粉。其激发峰350nm和415nm分别对应于Ce³⁺的4f→²D_<sub>5/2和4f→²D_3/2跃迁。随着Ba离子含量的增加,发射光谱峰值波长由530nm红移至590nm,发射光全半宽度由85nm增加至160nm。Ba²⁺的最佳掺杂浓度为0.35mol。将0.35Ba²⁺共掺Sr₃SiO₅:0.018Ce³⁺,0.018Li⁺与蓝光IngaN LED芯片（峰值波长为460nm）封装,在前向驱动电流为20mA下,获得了显色指数为86的白光LED。研究了分别掺杂Ba²⁺,Ca²⁺,Mg²⁺的Sr₂SiO₄:Eu²⁺的黄色荧光粉。三个系列样品在340nm-450nm范围都有较强的激发。以Sr_1.73Ba_0.02SiO₄:0.07Eu²⁺的激发和发射效果最好,其发射波段范围为520nm-620nm,这归因于占据六配位的Sr²⁺（Ⅱ）的Eu²⁺的4f⁶5d→⁸S_7/2跃迁。Ba²⁺、Eu²⁺的最佳掺杂分别为0.2mol和0.07mol。将Sr_1.73Ba_0.2SiO₄:0.07Eu²⁺与蓝光InGaN LED芯片（峰值波长为460nm）进行封装,在20mA前向驱动电流驱动下,得到了显色指数为85的白光LED。研究了能被近紫外激发的高效BaMgAl₁₀O₁₇:Eu²⁺（BAM）蓝色荧光粉;制备了BAM蓝光荧光粉,研究了其光谱特性,研究了BAM的受热后发光衰减机理,并且通过分析BAM晶格结构,研究了增加Mg²⁺的含量来提高BAM的稳定性,得出了提高BAM热稳定性的最佳Mg²⁺的总摩尔浓度为1.05mol。研究了两个系列的硅酸盐的红光荧光粉:M_3-xSiO₅:xEu³⁺（M=Mg,Ca,Ba,Sr）和ca(La_1-xEu_x)₄Si₃O₁₃。它们可以作为补偿蓝光芯片加YAG黄色荧光粉封装的白光LED的红色成分的红色荧光粉,也可以作为近紫外芯片激发的三基色白光LED中的红光荧光粉。研究了Ba_2-xMg_1-ySi_2-zAl_zO₇:xEu²⁺,yMn²⁺系列白光荧光粉。当Al³⁺的掺杂浓度为0.3mol时,样品具有最佳的发射效果,是一个从400nm-650nm的宽波段发射,包含三个发射峰,峰值波长分别为:623nm,501nm和438nm。其中438nm和501nm的发射源于在晶格中取代了Ba（Ⅱ）和Ba（Ⅰ）的两种Eu²⁺的5d→4f的能级跃迁。623nm的发射源于Eu²⁺将一部分能量转移到Mn²⁺,Mn²⁺产生⁴T₁→⁶A₁的能级跃迁。Al³⁺的掺杂能够调节样品发射蓝光（438nm）和绿光（501nm）的相对强度。将样品分别与380nm芯片,405nm芯片和460nm芯片进行封装,得到三种白光LED,其中以380nm芯片加该样品封装的显色指数最高,达到86,计算出来的色坐标是（0.3183,0.3136）,超过了当前460nm芯片加YAG黄色荧光粉的显色指数。更多还原

【Abstract】 White light-emitting diodes are considered as the fourth generation of solid-state lighting sources for their excellent properties such as high luminous efficiency,long lifetime,energy saving,subsize,stability and lack of toxic mercury.Compared with incandescence and fluorescence,they meet our demands for safety,energy saving and environment protection in a higher level for illumination products.Using a blue LED chip coated with a yellowish phosphor of YAG:Ce³⁺ is the widely used technique to produce white light LED.However,for lacking of red component in the emission spectrum,this kind of white LED suffers from the drawbacks of high color temperature,blue/yellow color separation and poor color rendering index（CRI）.The drawbacks of high color temperature and low color rendering index become two barriers in using white LED as general illuminations sources.It is important to broaden the YAG’s emission spectrum or to find out other yellow/yellow-orange phosphor with wider emission spectrum than what YAG has for the new generation of solid-state illumination.High temperature solid reaction method is widely used in phosphor synthesizing for advantages of easy operation and high success rate;while microwave radiation method is a newly-developed method which has been adopted since 1980s,showing advantages of high efficiency and rapid,uniform heating,and so on.In this work, series of phosphors for white LED were synthesized by combining the two methods, i.e.,the microwave radiation and high temperature solid reaction methods.Firstly,series of Ba²⁺ codoped Sr₃SiO₅:Ce³⁺,Li⁺ samples were synthesized and studied.It was found that the excitation wavelengths peaking at 350nm and 415nm attribute to the transition of 4f→²D_3/2 and 4f→²D_5/2 of the Ce³⁺ ions,respectively. Through transitions of 5d→4f in Ce³⁺,the phosphors showed a very broad and strong yellow emission under near ultraviolet（UV） or blue light excitation.Red shift of emission band from 530nm to 590nm has been achieved by adding the element Ba²⁺ in the Sr₃SiO₅host.The optimum doping concentration of Ba²⁺ is 0.35mol.Under a forward bias current of 20mA,white LED with a color rendering index of 86 was obtained by combining an InGaN LED chip（460nm） with 0.35Ba²⁺codoped Sr₃SiO₅:0.018Ce³⁺,0.018Li⁺.Secondly,series of Ba²⁺,Ca²⁺,Mg²⁺ codoped Sr₂SiO₄:Eu²⁺ yellow phosphors were synthesized and studied.These samples can be excited by light ranging from 340nm to 450nm efficiently.Among them,the phosphor Sr_1.73Ba_0.2SiO₄:0.07Eu²⁺ has the best excitation and emission efficiency.Sr_1.73Ba_0.2SiO₄:0.07Eu²⁺ has the emission spectrum ranging from 520nm to 620nm,attributing to the transition of 4f⁶5d→⁸S_7/2 of Eu²⁺, which occupies the site of sexadentate Sr²⁺（Ⅱ） in the host crystal.The optimum doping concentrations of Ba²⁺ and Eu²⁺ are 0.2mol and 0.07mol.Under a forward bias current of 20mA,white LED with color rendering index of 85 was obtained by combining an InGaN LED chip（460nm） with Sr_1.73Ba_0.2SiO₄:0.07Eu²⁺.Thirdly,series of high efficiency BaMgAl₁₀O₁₇:Eu²⁺（BAM） blue phosphors were studied.The luminescence and the principle of the degradation of BAM were studied. Through analysis of the crystal structure of the BAM,we found that the BAM’s thermally stability can be improved by adding additional Mg²⁺ ion,and the best sample was achieved with 1.05mol Mg³⁺.Fourthly,two series of m_3-xSiO₅:xEu³⁺（M=mg,Ca,Ba,Sr） and Ca(La_1-xEu_x)₄Si₃O₁₃ silicate red phosphors were studied.The two phosphors can be used as the compensation of the red spectrum for the white LED using a blue LED chip plus YAG yellow phosphor.In addition,they can be used as the red phosphor for the three primary colors white LED excited by a near ultraviolet LED chip.Finally,series of Ba_2-xMg_1-ySi_2-zAl₂O₇:xEu²⁺,yMn²⁺ were studied.As the concentration of the Al³⁺ is 0.3mol,the sample has the optimum emission spectrum ranging from 400nm to 650nm.The emission band consists of three peak wavelengths located at 623nm,501nm and 438nm,respectively.The emission peaks at 438 and 501nm originate from the transition of 5d→4f of Eu²⁺ ions that occupy sites of Ba（Ⅱ） and Ba（Ⅰ） in the host crystal,while the emission at 623nm is attributed to the transition of ⁴T₁→⁶A₁ of Mn²⁺.The relative emission intensity of the peaks at 438nm and 501nm can be modulated by changing the concentration of Al³⁺.Three white LEDs were obtained by combining the sample phosphor with LED chips at 380nm, 405nm and 460nm,respectively.Among them,the 380nm case has the best color rendering index of 86,and the CIE chromaticity coordinates is（0.3183,0.3136）.更多还原