兰州大学机构库 >材料与能源学院
Alternative TitlePreparation and properties of oxide luminescent materials for NUV-LED
Thesis Advisor王育华
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name理学硕士
Degree Discipline物理学
KeywordNUV-LED NUV-LED 氧化物发光材料 oxide luminescent materials 热稳定性 thermal stability Eu2+ Eu2+

白光LED作为新一代的照明光源,因其高效、环保、节能等优点而受到广泛应用。随着科技的进步和生活质量的提高,人们对“健康照明”的需求日益增长,这也使得LED光源需要具备更高的性能。尤其是在室内照明领域,光源除了“高亮度”的基本需求外,还应兼顾高显色指数、适宜色温等适应人眼健康指标的“高品质”需求。“近紫外LED芯片+多色荧光粉”的组合方式(NUV-LED,Near ultraviolet light-emitting diodes)得到的白光在提高显色指数和色温调节等方面独具优势,已逐渐成为白光LED的首选方案。然而,目前能够应用于NUV-LED的发光材料还存在着较多的问题,如热稳定性差、制备条件苛刻、激发波长不适宜以及对蓝(绿)光重吸收等。针对以上关键问题,本论文对两种Eu2+掺杂的氧化物发光材料体系展开深入研究,通过离子取代工程,一方面改善了(Sr, Ba)2SiO4: Eu2+绿色商用荧光粉热稳定性低的问题,另一方面开发了一种近紫外激发的超宽带黄色发光材料,并围绕离子取代对它们发光性能的影响进行了深入研究。具体研究内容和主要结果如下:

1. 利用K+、Na+等碱金属离子取代,通过高温固相法,在1400 ℃还原气氛下成功制备了一系列Sr0.98-xAxBaSiO4-xFx: 0.02Eu2+ (A = K, Na;0 ≤ x ≤ 0.4)发光材料。K+和Na+对SrBaSiO4: Eu2+晶格中Sr2+的取代可以明显改善样品的结晶性,并抑制Eu2+发光中心之间的能量传递,使得荧光粉的发光强度显著增强。同时,K+和Na+取代后,使样品具有更强的结构刚性,降低了5d电子在高温下自电离的概率;并且由于引入了更深的陷阱能级,在陷阱补偿机制的共同作用下,使得SrBaSiO4: Eu2+荧光粉的热稳定性得到大幅提升,在150 ℃时,其发光强度可提升至室温下的81.48%。

2. 以氟磷酸盐(K, Rb)2CaPO4F为研究对象,利用同主族阳离子取代,在较低温度下(750 ℃)制备了(K, Rb)2Ca0.98-xMgxPO4F: 0.02Eu2+系列发光材料。X射线衍射图谱显示,不同Mg2+取代浓度的样品均可以形成良好的单相。Mg2+的取代可以减少(K, Rb)2CaPO4F: Eu2+发光中心的能量传递,增强固溶体结构刚性,从而使其发光强度和热稳定性均得到显著增强。(K, Rb)2CaPO4F: Eu2+荧光粉的发射波长在Mg2+取代后可按K/Rb比的不同在665-487 nm内连续移动。在K/Rb比为1 : 1时,Mg2+取代后的KRbCa0.78Mg0.2PO4F: 0.02Eu2+样品表现出超宽带的黄光发射,其内外量子效率分别可达58.90%和32.47%,发射带覆盖除蓝光外的大部分可见光光谱区域,峰值位于580 nm左右,发射半高宽达181 nm;其激发带覆盖了近紫外到蓝光的区域,峰值位于380 nm附近,可以高效匹配近紫外芯片。采用制备的超宽带黄色发光材料作为黄光成分进行了白光NUV-LED器件封装,该器件发出的白光具有高显色指数(Ra = 92.3)、适宜的相关色温(5644 K)和CIE色度坐标(0.3292, 0.3450),并且在不同驱动电流下表现出优异的颜色稳定性,证明该超宽带黄色发光材料在白光NUV-LED领域极具应用潜力。

Other Abstract

White light-emitting-diodes (WLEDs), a new generation of lighting source, have been widely used due to their high efficiency, environmental friendliness and energy-saving properties. Yet, people’s demand for “healthy lighting” increases as science and technology advance and the quality of life improves, leading to higher performance requirements for LED light sources. Especially in the aspect of indoor lighting, in addition to the basic requirement of "high brightness", the light source should also take the "high quality" requirements of high color rendering index, appropriate color temperature and other indicators suitable for human eye health into account. The combination of "near ultraviolet LED chip + multi-color phosphor" (NUV-LED, Near ultraviolet light-emitting diodes) has unique advantages in improving color rendering index and color temperature adjustment, and has gradually become the preferred solution for WLEDs. However, the existing luminescent materials can be applicated for NUV-LED are still limited by some serious shortages, such as poor thermal stability, harsh synthesis process, inappropriate excitation, and the reabsorption of blue or green light. In view of these key problems, two kinds of Eu2+-doped oxide luminescent materials have been studied in this thesis. Through the ion substitution engineering, on the one hand, we improved the thermal stability of green commercial (Sr, Ba)2SiO4: Eu2+ phosphor; On the other hand, a NUV-excited ultra-broad band yellow emission phosphor has been developed, and the effect of ion substitution on their luminescent properties was studied in depth as well. Specific work and main results of this thesis as follows:

1. By the substitution of K+ and Na+, a series of Sr0.98-xAxBaSiO4-xFx: 0.02Eu2+ (A = K, Na; 0 ≤ x ≤ 0.4) have been successfully prepared by high-temperature solid-state method under 1400 ℃ in the reduction atmosphere. The substitution of K+ and Na+ for Sr2+ in the SrBaSiO4: Eu2+ lattice can improve the sample’s crystallinity and inhibit the energy transfer between emission centers of Eu2+, resulting in a significant increase in the luminescence intensity of the phosphor. Meanwhile, the structure rigidity can be enhanced by the substitution of K+ and Na+, which reduces the probability of the auto-ionization process of 5d electrons at high temperatures. Moreover, due to the introduction of deeper trap levels, by the joint effect of trap compensation mechanism, the thermal stability of SrBaSiO4: Eu2+ phosphor can be greatly improved. At 150 ℃, its emission intensity can reach to 81.48% of that at room temperature.

2. Taking fluorophosphate (K, Rb)2CaPO4F as the research object, at a relatively low temperature (750 ℃), a series of (K, Rb)2Ca0.98-xMgxPO4F: 0.02Eu2+ luminescent materials were prepared by using the same main group cation substitution. Good single-phase sample can be formed in varying substitution concentration of Mg2+, which can be proved by the X-ray diffraction patterns. After the substitution of Mg2+ for Ca2+, by repressing the energy transfer between the emission centers and strengthening the structure rigidity, the emission intensity and thermal stability of (K, Rb)2CaPO4F: Eu2+ solid solution was significantly increased, while the emission wavelength of the solid solution can move continuously in the range of 665-487 nm according to the K/Rb ratio. Substituted by Mg2+, the obtained sample of KRbCa0.78Mg0.2PO4F: 0.02Eu2+ shows an ultra-broad band yellow light emission with an internal and external quantum efficiency of 58.90% and 32.47% respectively, whose emission band covers most of the visible light spectral area except blue light, with the peak at about 580 nm and a 181 nm emission full-width half-maximum. Its excitation band covers the region from NUV to blue light, peaking around 380 nm, which effectively matches the NUV chip. The fabricated NUV-LED device by using this ultra-broad band yellow emission phosphor as the yellow component can emit bright white light with high color rendering index (Ra = 92.3), appropriate correlated color temperature (5644 K) and CIE chromaticity coordinates (0.3292, 0.3450), and shows excellent color stability under different driving currents, indicating that this ultra-broad band yellow emission phosphor has great application potential in the field of NUV-LED.

Subject Area固体发光材料
MOST Discipline Catalogue理学 - 物理学
Other Code262010_220200937711
Document Type学位论文
Recommended Citation
GB/T 7714
刘政强. NUV-LED用氧化物发光材料的制备及性能研究[D]. 兰州. 兰州大学,2023.
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