La2CaB8O16:Eu3+，Bi3+红色荧光粉的双格位取代形成机制及其发光性能研究

White light-emitting diodes (W-LEDs) are known as the 4th generation light sources for theirs advantages, such as small size, high luminescence efficiency, long lifetime, low power consumption, and environmental friendliness. There are two approaches to produce phosphor-converted W-LEDs. The first approach is to combine a blue LED (460 ± 10 nm) with a yellow-emitting phosphor based on YAG:Ce, which is the most popular and commercially available method. However, the W-LEDs obtained by this way have poor color-rendering index and high color temperature for lack of red component. The second one is to excite red, green and blue phosphors with a near-UV LED (370-410 nm), which is considered as a most convenient and effective way to obtain high quality W-LEDs. The very important constituent of this way is the phosphor which can be effectively excited by near-UV light. The currently available phosphor materials for solid-state lighting (SSL) devices based on near-UV LEDs are mainly red phosphor Y2O2S:Eu3+, green phosphor ZnS:Cu+/Al3+, and blue phosphor BaMgAl10O17:Eu2+. Unfortunately, the efficiency of the red phosphor Y2O2S:Eu3+ is much lower than that of green or blue phosphor for its weak excitation in the range of 370-410 nm. Therefore, there is an urgent need to develop superior red phosphors suitable for near-UV excitation. La2CaB8O16:Eu3+ is a double-site substitution rare earth-alkaline earth metal complex borate newly developed as a red emitting phosphor. The phosphor has a broad and strong absorption at 394 nm, and can produce an intense red emission at about 615 nm under near-UV LEDs excitation. On the basis of the existing work，a double-site substitution red phosphor La2CaB8O16:Eu3+, Bi3+ will be studied intensively and systematically in this project. The main contents include that the distribution model of luminescence centers in La2CaB8O16:Eu3+, Bi3+ phosphor will be built, and that the luminescence mechanism of Eu3+ and the energy transfer mechanism of Bi3+-Eu3+ will be investigated, and that the effect of composition variations on photoluminescent properties of solid solution phosphors by substitution of Ba2+/Sr2+ for Ca2+ in La2CaB8O16:Eu3+ will be discussed. We have independent intellectual property of the phosphor, and believe that the successful implementation of this project will help to further promote the practical application and industrialization of the white LED solid state lighting.

开发新型白光LED用的高效红色荧光粉是当前固态照明领域的研究热点。本项目选择La2CaB8O16:Eu3+，Bi3+为对象，对其双格位取代形成机制和发光机理进行深入、系统地研究。采用分子动力学、第一性原理进行模拟和计算，结合结构分析和光谱分析，建立不同发光中心的分布模型，进而了解荧光粉的双格位取代形成机制；通过测试和分析荧光粉的室温和低温光谱、荧光寿命，以及高分辨光谱，获得Eu3+的发光机理和浓度淬灭机制，以及Bi3+与Eu3+的能量传递方式和敏化机制；通过研究荧光粉基质组分改变对Eu3+的晶体场环境的变化，进而理解荧光粉的组分变化对其发光性能的影响规律，确定最优的组分比例，从而提高荧光粉红光发射的强度和纯度。

开发高效稳定的白光LED用红色荧光粉仍是当前固态照明领域的研究热点，本项目以La2CaB8O16:Eu3+，Bi3+为对象，通过改进制备技术和优化合成工艺参数，以改善荧光粉微观形貌和发光性能；采用理论模拟与计算及光谱分析等，理解荧光粉的双格位取代形成机制；研究光谱性能，获得Bi3+与Eu3+的能量传递方式和敏化机制，以及温度淬灭机制；研究基质组分改变对荧光粉光谱特性的影响，理解荧光粉的组分变化对其发光强度与发光纯度的影响规律。.溶胶-凝胶法和共沉淀法是合成具有性能优异的目标荧光粉的适宜制备技术，其最优合成参数分别为：溶胶-凝胶法（烧结温度900 ℃、溶液pH值7~8、柠檬酸根与阳离子摩尔比1.0，及添加少量PEG），共沉淀法（氨水浓度20%、溶液pH值9、共沉淀温度60 ℃、共沉淀时间24 h，热处理温度800 ℃与时间3 h）。.根据理论模拟与计算及XPS谱分析，Eu3+既可以取代基质中的La3+，也可以取代Ca2+，但取代La3+的几率要大于Ca2+，因为Eu3+取代Ca2+会引起系统能量的升高和离子的成键过饱和度增加，而取代La3+能降低体系的能量和离子的成键过饱和度。通过低温高分辨光谱分析，确定了各激发波长和发射波长与格位占位对应关系，还确定两个发光中心（La格位和Ca格位）之间存在能量传递，即存在CTB Eu(Ca)→CTB Eu(La)，5L6 Eu(Ca)→5L6 Eu(La)和5D0 Eu(La)→5D0 Eu(Ca)三种能量传递过程。确定了Eu3+(La)和Eu3+(Ca)的能级示意图。.La2CaB8O16:Eu3+，Bi3+荧光粉中Bi3+与Eu3+离子间存在能量传递，其相互作用属于电偶极-电偶极作用。该荧光粉具有优异的温度稳定性，470 K温度下红光发射强度仍然超过室温时的60%，其温度淬灭的原因是Eu3+离子4f6电子与电荷转移态CTS之间发生了交叉弛豫过程，曲线拟合并计算可得到热激发能为0.17 eV，淬灭温度为508 K。.以Ba2+（或Sr2+）取代Ca2+，通过改变基质组成可以能明显改善荧光粉的红光发射强度和红光/橙光比，当取代量x=0.6（Ba2+）和x=0.8（Sr2+）时达到红光发射强度及红/橙比均取最大值。.本基金项目的研究，为研究与开发高效、稳定的双格位取代La2CaB8O16:Eu3+，Bi3+的荧光粉提供了理论依据。