多铝酸盐晶体结构调制的3d3电子态Mn4+/Cr3+荧光增强机制研究

Red-emission phosphors excited by blue or near-ultraviolet LED chips (n-UV LEDs) (380-420 nm) have been intensively investegated in recent years.Usually, the most frequently used red phosphors for LEDs are rare earth (RE) ions doped nitride/oxynitrides, such as CaAlSiN3:Eu2+, BaY2Si2Al2O2N5 : Eu2+, most of starting materials of those phosphors are either nitrides of the alkaline-earth elements or rare earth elements, which are expensive or difficult to synthesis and handle, because high nitrogen pressures are required for their synthesis. Consequently, the search for less expensive, facile for synthesis, has been a long-standing and important issue in new phosphors development. Mn4+/Cr3+ doped red emission phosphors attracted special interest because of their ability to function at unusually high temperatures under ultraviolet excitation. In fact, transition metal ion with electron configuration dn (0< n< 10) is of a broad and strong absorption band in UV region due to ligand to metal charge-transfer. Therefore, the transition metal ions have potential applications in developing high efficient UV-chip LED devices. In this project, our proposes are based on our previous research results. Special attention is paid to the crystal field analysis of the experimental features in relation to the structural data, and forcus on the peculiar features of the chemical bonding and effects of electron-phonon coupling of Mn4+/Cr3+ doped aluminates. The correlation between site symmerty of Mn4+,Cr3+ in hosts and their quantum efficiency will be charaterized. A precise which can effectively and easily describe ionicity/ covalence of the transition metals doped crystals criterion will be proposed. In addition, we will carry out a temperature-dependence research, XMCD research and XANES research related to the luminescence properties. Above all, the results of our project will give us a lot theory hints and the exploitation wrinkles of phosphors with high efficiency.

在照明和显示领域，高效、廉价的红色荧光材料研究备受关注。为了获得高效3d3电子态Mn4+/Cr3+激活红色荧光材料，本项目拟在晶体结构类型丰富的多铝酸盐中开展Mn4+/Cr3+发光效率与Al-O多面体对称性的关联性研究。本项目通过在低温态对基质电子结构和激活剂离子中间能级的研究，获得抑制声子参与发光行为的有效手段；通过同步辐射X-射线磁性圆二色（XMCD）探测Mn4+/Cr3+在晶格中的占位及其价态变化情况；通过X-射线吸收近边结构(XANES)谱获取Mn4+/Cr3+在晶格环境的变化情况，揭示晶体结构构型以及缺陷态对激活离子周围局域环境及其电子结构的影响规律以及电荷转移规律性。研究结果对Mn4+/Cr3+发光效率的改善和新型发光材料的筛选及制备具有重要指导意义和理论价值。

本项目针对过渡金属离子Mn4+/Cr3+在无机发光材料中的发光行为进行了研究，就其发光的基本物理过程和应用进行了理解和表征。其中主要关注的发光材料有：Sr4Al14O25:Mn4+、CaAl12O19:Mn4+/Cr3+、La2LiTaO6:Mn4+以及这些发光材料与稀土离子共掺杂等情况的研究。着重点有两点，第一：Mn4+/Cr3+离子在不同化合物杂质能级位置的确定。过渡金属离子Mn4+/Cr3+在不同化合物中的杂质能级具有规律性，其与基质导带的相对位置影响到其发光效率。通过光谱信息测试和分析我们发现，Mn4+和Cr3+具有规律性电荷迁移带，并且具有稳定的束缚能级。通过分子轨道理论和Chemical shift model，我们阐释了导致杂质能级不发生变化的主要原因，也阐述了相应的变化趋势。第二，Mn4+/Cr3+离子价态的稳定和电荷补偿关系，通过电荷补偿，提高激活剂离子价态的稳定性，并提高离子的猝灭浓度，进而达到提高Mn4+/Cr3+的发光效率。研究发现，Mn4+和Cr3+均可实现红色发射，该波段可以显著改善LED用发光材料在深红色波段的色域，可以结合蓝光芯片和黄色荧光粉改善现有白光LED的显色性。.相关研究成果对改善材料的发光性质、理解Mn4+/Cr3+的发光本质具有重要意义；而且，该研究对于理解整个3d轨道电子在无机材料中的束缚能级、过渡金属离子的物理过程、新型过渡金属离子的设计等具有非常重要的参考意义。