兰州大学机构库 >物理科学与技术学院
近紫外及蓝光激发的LED用氧化物基发光材料的制备及其性能研究
Alternative TitlePreparation and photoluminescence properties of oxide based w-LED used materials under near-ultraviolet or blue light excitation
丁鑫
Subtype博士
Thesis Advisor王育华
2018-05-30
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword白光LED 固相反应 稀土离子 晶体结构 发光性质
Abstract

白色发光二极管(简称w-LED)固体光源作为最新代照明器件,以其革命式的优良性质已经受到越来越多的关注。常用白光LED产生的方式有三基色芯片组合法和芯片加荧光粉组合法(荧光转换法,简称pc-LED)。其中荧光粉材料是产生白光的不可或缺的关键因素。pc-LED中的代表即蓝光芯片加黄色荧光粉法是目前市场上使用最广泛的方式之一;为了解决蓝光芯片加黄色荧光粉的先天缺陷,另一类pc-LED的产生方式即近紫外芯片加三基色荧光粉也逐渐被广泛研究。本论文针对pc-LED两种产生方式存在的一些关键问题,通过材料结构设计,结构精细化研究,合成条件控制,理论模拟,发光性质表征等手段系统地研究了几种近紫外和蓝光激发的氧化物发光材料,其主要研究内容和结果如下:

1.针对目前近紫外激发的蓝光和绿光荧光粉存在的问题,使用高温固相法合成了三种在可见光范围内短波长发射的发光材料。K2ZrSi3O9: Eu2+蓝色-绿色发光材料,分别使用XRD精修,透射电镜,光致光谱,反射光谱等手段研究了其结构,发光,离子占位等情况。在400 nm的近紫外光激发下K2ZrSi3O9: Eu2+表现出波长在465 nm的蓝光发射,分别使用Al3+和Sc3+离子进行电荷补偿,由于离子半径差和对晶体产生畸变的影响不同,发现Al3+的加入不会改变Eu2+在晶格中的占位,Sc3+的加入使得Eu2+更倾向于占据Zr4+的格位,进而发射绿光。因此在同一基质中通过不同的电荷补偿离子实现了蓝光和绿光发射。通过离子对的取代合成了一种近紫外激发的绿色发光材料Ba5(PO4)2SiO4: Eu2+,这种材料是以Ba5(PO4)3F为结构原型,用[PO4]3- + X-→[SiO4]4-取代方式合成的。这种发光材料的最强激发在400 nm左右,能够实现波长在516 nm左右的绿光发射,研究发现Eu2+占据两种不同晶体场环境的格位,发射峰能够拟合为两个单峰。由于较低的热激活能使得该发光材料的热猝灭性质较差。通过与商用蓝粉BAM: Eu2+和红粉CaAlSiN3: Eu2+混合,配合近紫外芯片成功制作了具有暖白光发射的LED。Ca3Hf2SiAl2O12: Ce3+是具有典型石榴石结构的青光发光材料,通过XRD精修及透射测试,首次确定了其具体的晶胞数据。该发光材料在400 nm的近紫外光激发下能够实现波长在450-550 nm范围内的青光发射,青色发光的发光材料能够有效的补充用三基色荧光粉产生白光时蓝光和绿光之间的缺失部分。该发光材料在150oC仍能保持70%以上的发光强度,发光效率较高,具有不错的应用价值。

2.针对目前近紫外激发的红橙光发光材料的问题,研究了两种长波长发射的发光材料,包括Sr9(Li, Na, K)Mg(PO4)7: Eu2+,LiBa12(BO3)7F4: Eu2+。Sr9(Li, Na, K)Mg(PO4)7: Eu2+在400 nm近紫外光激发下具有半高宽为100 nm以上的橙光发射。其发射光谱覆盖范围广,且具有部分红光发射,在制作白光LED中能够有效避免红光缺失的情况。在该系列发光材料中,以Sr9LiMg(PO4)7: Eu2+为研究重点,发现Eu2+在晶体中有三种不同的发光环境,分别能够发射波长在527,608和680 nm的宽带可见光。该发光材料的热猝灭性质较差,是因为在该晶体结构中的多面体均以刚性较弱的共点连接,导致高温下晶格易发生扭曲变形。在940oC较低温度下合成了一种红色发光材料LiBa12(BO3)7F4: Eu2+,该发光材料在400 nm激发下能够发射波长在650 nm的红光,其半高宽为89 nm。在该晶体结构中有特殊的环状通道结构,且Ba2+呈现均匀的层状排列方式。Eu2+占据三种不同的Ba2+格位,通过MS(Materails Studio)理论模拟发现,该基质具有3.67eV的直接带隙,将1%的Eu2+掺杂到不同格位后发现带隙中存在着不同的Eu2+的基态和激发态能级,不同基态与激发态之间的能量差与发射光谱中三个发射峰对应的能量相一致。通过与商用BAM: Eu2+,(Sr, Ba)2SiO4: Eu2+混合,用三基色的方式制作了暖白光LED,其色坐标、色温、显色指数和流明效率分为(0.3475, 0.3416)、4856 K、84.1和72.6 lm/W。

3.针对蓝光激发的红色荧光粉存在的问题,开发了两种非稀土离子Mn4+掺杂的红色发光材料。设计合成了两种Mn4+掺杂的红光材料Mg3Ga2GeO8: Mn4+和K2Ge4O9: Mn4+。Mg3Ga2GeO8: Mn4+是MgGa2O4-Mg2GeO4尖晶石固溶体的中间相,Mn4+占据了其中的八面体配位的Mg2+/Ga3+格位,通过Li+的电荷补偿,发光强度有了明显提高。该发光材料的最强激发在420 nm附近,接近蓝光,同时也具有较强的近紫外激发。用近紫外芯片与BAM: Eu2+和(Sr, Ba)2SiO4:Eu2+混合,制作的暖白光LED的色坐标为(0.316, 0.375),色温为3440K。K2Ge4O9: Mn4+的合成温度为900oC。其激发光是蓝光,在450 nm附近,能够发射波长在663 nm附近的红光。Mn4+同样占据了晶体中八面体格位。由于Mn-O电荷迁移带的作用使得该荧光粉的热猝灭性质较差。该发光材料能有效的补充蓝光芯片与黄色荧光粉产生冷白光中缺少的红光部分。使用蓝光芯片将K2Ge4O9: Mn4+与YAG混合之后得到的白光LED的色温从6343K下降到3119K,显色指数从65.4增加到84.1。

Other Abstract

White light-emitting diode (referred to as w-LED) solid-state light source as the latest generation of lighting devices, with its revolutionary nature of the excellent has received more and more attention. Common white LED production methods are the three primary color chip combination method and chip plus phosphor combination (fluorescence conversion method, referred to as pc-LED). Among them, phosphor material is an indispensable key factor for producing white light. The blue chip plus yellow phosphor method as the representative in pc-LED is one of the most widely used way currently on the market; in order to solve the blue chip plus yellow phosphor of birth defects, another type of pc-LED production that is near-ultraviolet chip plus trichromatic phosphors have also been widely studied. In this thesis, some problems existing in the two production modes of pc-LED are investigated systematically by means of material structure design, structure refinement, synthesis condition control, theoretical simulation and luminescence property characterization. Several near-UV and blue-light excited oxidation luminous materials, its main research are as follows:

1. Aiming at the problems of near-ultraviolet excited blue and green phosphors, three kinds of luminescent materials with short wavelength emission in visible light range were synthesized by high temperature solid-state method. K2ZrSi3O9 and Eu2+ activated K2ZrSi3O9 have been studied to explore the new materials for phosphor-converted white light near ultraviolet light-emitting diodes (NUV-LEDs). The CIE chromaticity coordinates and FWHM of the blue phosphor K2ZrSi3O9: 1%Eu2+ are (0.1538, 0.1857) and 57 nm. The photoluminescence properties of co-doped Eu2+-Al3+and Eu2+-Sc3+ charge compensation pairs phosphors were investigated. The Eu2+ single-doped K2ZrSi3O9 phosphor shows blue emission with the broad-band peaking at 465 nm upon 400 nm NUV excitation. By Eu2+-Al3+ as charge compensation, the photoluminescence properties do not change distinctly, while the photoluminescence emission spectrum shifts to red area about 39 nm and becomes green emission by using Eu2+-Sc3+ pair. Different occupying situations with different charge compensation pairs were discussed. Blue and green emission can be yielded in K2ZrSi3O9: Eu2+ compound by different charge compensation mechanism. It reveals that K2ZrSi3O9: Eu2+ possesses remarkable optical properties and can be used in NUV-LEDs. A novel apatite mineral of Ba5(PO4)2SiO4 was synthesized successfully. Ba5(PO4)2SiO4 was found to be hexagonal crystal system and the space group is attributed to P 63/m (176). Ba5(PO4)2SiO4:Eu2+ can emit green light peaking at ~515 nm under 405 nm NUV excitation with quantum efficiency 31.89%. According to structure and photoluminescence (PL) properties analysis, Eu2+ can occupy two kinds of Ba2+ site. It has not good temperature stability properties because of too much temperature-dependent electron–phonon interaction at high temperature. The fabricated white-LEDs using a 405 nm GaN NUV chip combined with a blend of RGB phosphors: CaAlSiN3:Eu2+, Ba5(PO4)2SiO4: 1%Eu2+ and BAM: Eu2+, driven by 30 mA current can get warm-white light with chromaticity coordinates (0.355, 0.342) and correlated color temperature (CCT) 4561 K. A new garnet compound Ca3Hf2SiAl2O12 and a series of Ce3+-doped phosphor Ca3Hf2SiAl2O12: xCe3+ were synthesized. Ca3Hf2SiAl2O12 belongs to body-centered cubic and Ia-3d (230) space-group with a = 12.3666 Å. Ca3Hf2SiAl2O12: xCe3+ took on broad excitation bands at 330 and 400 nm attributed to Ce3+ characteristic 5d-4f transition and can emit cyan emission under 400 nm UV light excitation. The emission intensity of CHSA: 1%Ce3+ phosphor can reach to 68.9% of YAG: Ce3+ (commercial) and 72.1% of Ca8Mg(SiO4)4Cl2: Eu2+ (commercial). In the process of increasing the temperature from 25 °C to 250 °C, the integrated emission intensity of Ca3Hf2SiAl2O12:0.5%Ce3+ is only decreased to 57.8% (250 °C) and shows nice thermal stability comparing with commercial  YAG: Ce3+(P46-Y3). Furthermore, Ca3Hf2SiAl2O12: 0.5%Ce3+ exhibits outstanding quantum efficiency (74.7%).

2. In order to solve the problem of near-ultraviolet excited red-orange light-emitting materials, two kinds of long-wavelength emission phosphors were developed. Sr9(Li, Na, K)Mg(PO4)7 was found to be trigonal, belonging to R-3m (166) space group. As a representative, the PL properties of Sr9LiMg(PO4)7: Eu2+ are investigated detail. It can emit orange light peaking at 635 nm with 405 nm excitation. According to structure and photoluminescence (PL) properties analysis, Eu2+ can occupy three kinds of Sr2+ site. By tuning weight ratio of blue and orange phosphors, the fabricated white-LEDs using a 405 nm GaN NUV chip combined with a blend of blue phosphor BAM: Eu2+and orange emitting Sr9LiMg(PO4)7: 0.04Eu2+ phosphor driven by 30 mA current can get tunable white light with chromaticity coordinates from (0.3535, 0.3011) and CCT 4287 K to (0.4036, 0.3539) and 3131 K. LiBa12(BO3)7F4: Eu2+ can emit red light peaking at ~644 nm under NUV excitation with the coordinate at (0.6350, 0.3586) and a sensitive color gamut for eyes. This phosphor with a kind of special tunnel crystal structure and layered distribution of Ba2+ is contributed to longer wavelength emission. By theoretical calculation and analysis using local state density energy band structure simulation of Eu2+ doped in different site, the origin of the observed emission center is distinguished. Temperature dependent PL spectra appeared anomalous phenomena that the intensity increases firstly and then decreases, which is due to the traps energy level’s contribution of electron’s transition. The phosphor also has cathodoluminescence (CL) property which the spectra take on typical current saturation phenomenon. And the CL curves indicated that this phosphor has a very good stability under much electron beam bombardment time. After fabricated, combing with BAM, (Sr, Ba)2SiO4 and our red phosphor excited under 405 nm NUV chips, warm light LED was gotten, and, its CIE coordinate is (0.3475, 0.3416) and the CCT, Ra and luminous efficiency is 4856 K, 84.1 and 72.6 lm/W.

3. Aiming at the problem of blue-excited red phosphor, two kinds of red luminescent materials doped with Mn4+ have been developed. A series of novel red emission Mg3Ga2GeO8: Mn4+ phosphors under NUV and blue excitation are synthesized successfully by traditional high temperature solid-state reaction. It has one octahedral site and tetrahedral site in crystal structure. According to XRD and photoluminescence (PL) properties analysis, Mn4+ can occupy octahedral (Mg2+/Ga3+) site. T It can emit red light peaking at 659 nm under NUV excitation. The CIE chromaticity coordinates and FWHM are (0.295, 0.677) and 24 nm. It demonstrated that MGG: Mn4+ has high color purity. The PL intensity of MGG: 0.5%Mn4+ drops to 72% when the temperature is raised up to 150 oC. By tuning weight ratio of blue, green and red phosphor, the fabricated white-LEDs using a 405 nm GaN NUV chip combined with a blend of blue phosphor BAM: Eu2+, green phosphor Sr2SiO4: Eu2+ and red emitting MGG: Mn4+ phosphor driven by 40 mA current can get white light with chromaticity coordinates (0.316, 0.375) and CCT 3340 K. K2Ge4O9 can emit red light peaking at 663 nm under UV or blue light excitation. The CIE chromaticity coordinates and FWHM are (0.702, 0.296) and 20 nm which demonstrated that K2Ge4O9: Mn4+ has high color purity. By tuning weight ratio of yellow and red phosphor, the fabricated white-LEDs using a 455 nm InGaN blue chip combined with a blend of yellow phosphor YAG: Ce3+ and red emitting KGO: Mn4+ phosphor driven by 40 mA current can get white light with chromaticity coordinates (0.405, 0.356) and CCT 3119 K. It indicated that K2Ge4O9: Mn4+ is a potential red phosphor matching with blue LED chips to get warm white light.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229687
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
丁鑫. 近紫外及蓝光激发的LED用氧化物基发光材料的制备及其性能研究[D]. 兰州. 兰州大学,2018.
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