白光LED用Sr(1-x)BaxSi2O2N2:Eu2+(0≤x≤1)荧光粉的制备和微结构改变相关的发光机理的探讨

White light-emitting-diodes (LEDs) are considered as the most promising 4th generation illuminating light sources due to their tremendous advantages including high efficiency, energy conservation, environmental protection, long lifetime and so on. Phosphors are indispensible component for white LED devices, which are responsible for the latter luminescence performance. Oxonitridosilicates phosphors are consists of the net of SiX4(X = O，N) tetrahedrons, which have highly chemical and thermal stability. Recently, the Eu2+-actived Sr(1-x)BaxSi2O2N2 (0≤x≤1) phosphors attract more and more attention due to their excellent color-tunable luminescence from yellow to blue under the excitation of near UV or blue light chips. However, their structure-related luminescence mechanisms are not clear. The emission of Eu2+ is attributed to f-d transition, which is easily affected by crystal environment of host lattice including crystal field strength, coordination environment, covalence and so on. Therefore, it is very improtant to ascertain the real microsturcture environment of Eu2+ in Sr(1-x)BaxSi2O2N2:Eu2+ (0≤x≤1)systems for us to understand the structure-related luminescence mechanism. Here, we will prepare pure-phased Sr(1-x)BaxSi2O2N2:Eu2+ (0≤x≤1) phosphors through the non-stoichiometric two-steps solid state process and investigate the effect of different preparation conditions, cation substitution, flux etc., on their luminescence properties. In order to study the effect of the change of microstructure on Eu2+ luminescence properties in Sr(1-x)BaxSi2O2N2:Eu2+ (0≤x≤1), we will employ the Rietveld refinement and EXAFS technologies to analyze the coordination environment around Eu2+ ions. Moreover, the arrangement of O and N atoms around Eu2+ ions in Sr(1-x)BaxSi2O2N2:Eu2+ (0≤x≤1) can also be judged by the refinement of neutron diffraction data. Through the above study, we can verify the effect of structure on the luminescence of Eu2+ ions in Sr(1-x)BaxSi2O2N2:Eu2+ (0≤x≤1) phosphors, and thus can adjust luminescence colors, enhance efficiency and color rendering index, improve thermal quenching property to meet the different requirements of White LEDs.

白光LED作为第四代照明技术具有高效、节能、环保、长寿命等优点，其中荧光粉对其性能有至关重要的作用。Eu2+激活的Sr(1-x)BaxSi2O2N2 (0≤x≤1)氮氧化物荧光粉，具有高的化学和热稳定性，且在近紫外和蓝光激发下其发光颜色可以从黄光到蓝光进行调节，引起越来越多的关注。然而至今其详细的发光机理还不清楚。因Eu2+的f-d跃迁发射受基质晶格环境（晶体场强度、配位环境、共价性等）影响较大，所以弄清楚Eu2+在Sr(1-x)BaxSi2O2N2:Eu2+中所处的微结构环境对于理解其发光机理是非常有帮助的。本课题拟定通过Rietveld结构精修和电子吸收光谱技术探测Eu2+周围的局部微结构环境，利用中子衍射技术来探测Eu2+周围的氮氧排列，探讨微结构改变对其发光性能的影响，提出微结构改变相关的发光机理，以期通过结构的微改变来调控荧光粉的发光颜色、提高发光效率和衍色性，改善热猝灭性能。

本项目通过三年的研究，利用晶体结构的精细表征技术分析了Eu2+离子在Sr1-xBaxSi2O2N2:Eu2+（0<x<1）中真实的微结构环境，阐明了阳离子取代过程中Eu2+离子局部微观晶胞参数、晶胞体积、键长等结构参数的变化对其5d-4f跃迁发光性质的影响规律。揭示了Eu2+离子周围局部结构变化诱导的发光性质变化的机理。通过精细结构表征结合Rietveld 结构精修技术揭示了Sr1-xBaxSi2O2N2:Eu2+发光材料体系中随Ba掺杂出现的反常发射红移和蓝光发射机理。其中发射红移是由于相邻Ba-O键长增加导致Eu-O键长逐渐减小，从而使Eu2+离子5d轨道晶体场的劈裂增强；而反常的蓝光发射是由于Eu2+离子进入离子半径较大的Ba1格位，其5d轨道晶体场的劈裂减弱。通过高分辨透射电子显微镜技术我们还揭示了在Sr0.98-xBaxEu0.02Si2O2N2 (0.63 < x < 0.78) 和Sr0.98-xBaxEu0.02Si2O2N2 (0.78 ≤ x < 0.98) 两个系列中观察到的单相高效白光发射是由于不同发光颜色的晶相在纳米尺度的混合。此外，我们系统的研究了静态高压对Sr1-xBaxSi2O2N2:Eu2+（0<x<1）荧光粉固溶体物相和发光性质的影响，揭示了压力诱导晶体结构可逆变化造成的发光调控的机理。同时，我们还将阳离子取代策略扩展到稀土掺杂的磷酸盐和硅酸盐体系中，更为系统的研究和阐述了稀土离子周围微观结构变化对5d-4f跃迁发光的影响，初步阐明了在所研究的荧光粉体系中稀土4f5d电子结构的物性关联。在稀土掺杂的硅/磷酸盐体系中和磷灰石结构材料中通过组分取代中的阳离子取代策略，控制荧光粉中激活剂离子的格位占据、价态变化和能量传递，实现对荧光粉发光性质的调控和优化，得到一系列新颖的、发光性质可调控的荧光粉材料。最后，通过软化学方法改善了荧光粉的形貌、尺寸和表面形态，提高了荧光粉的发光效率和稳定性。总的来说，所提出的激活剂离子周围微结构变化诱导4f5d发光性质变化的机理具有一定的普适性，为新颖高效稀土掺杂氮氧化物和硅/磷酸盐体系荧光粉的制备和优化提供有效的理论支持。