蓝光激发的白光LED用红色发光材料的合成、改性及性能研究

A blue LED chip combined with a yellow emitting phosphor YAG:Ce is the most common way in commerical to obtain white light, but this technology has drawbacks such as a low color-rendering index (CRI usually < 75) and a relatively cool white light ( correlated color temperature, CCT is 4000-8000 K) because the deficiency of red component in the obtained spectrum. Adding red phosphor to this technology is considered as an efficient method to solve this problem, but the number of red-emitting phosphor materials which are adequate for high-luminance pc-LED applications is rather small. Sr2Si5N8:Eu2+ and CaAlSiN3:Eu2+ have found applications in commercially available illumination-grade white pc-LEDs. However, the rather broad emission bands of these materials greatly limit the maximum achievable luminous efficacies of high-quality warm-white pc-LEDs (CRI > 90) because a significant part of the light is produced outside the sensitivity range of the human eye above 700 nm. As a result, it is urgent to develop new narrow-band red-emitting phosphor. In this program, we proposed two ways to develop such red phosphors: (1) Incorporate nitrogen in the yellow emitting phosphors Sr2SiO4:Eu2+,Li2SrSiO4:Eu2+ and Sr3SiO5:Eu2+ by using different silicon sources (mesoporous silica, spherical silica, TEOS) via ammonia reduction and nitridation method, so as to red-shift Eu2+ emission in them; Investigate the reaction mechanism and the effect of annealing temperature and ammonia flow on the crystal structure and properties of the nitridized phosphors; (2) Synthesize the newly developed red emitting phosphor Sr[LiAl3N4]:Eu2+ by high temperature solid state reaction and carbon thermal reduction and nitridation methods, respectively; Improve its quantum efficiency by optimizing synthesis condition and Eu2+ doping concentration ; Decrease the local crystal field strength of Eu2+ in Sr[LiAl3N4]:Eu2+ by large cation ions substitution, in hope of adjusting Eu2+ emission to short wavelength (600-630 nm) and making Sr[LiAl3N4]:Eu2+ more appropriate for white LEDs.

红色荧光粉是提高白光LED显色性指数和流明效率的关键，但能满足要求的红色荧光粉十分缺少。CaAlSiN3:Eu2+和Sr2Si5N8:Eu2+是目前性能较好的红色荧光粉，但存在合成成本高和发射波长较长、光谱较宽(导致红外溢出)的缺点，不利于降低LED的成本和提高LED的流明效率。为此，本项目拟开展两方面工作：(1)使用活性较高的硅源，采用氨气还原氮化工艺对发光效率较高的Eu2+掺杂黄色发光材料进行氮化，调制Eu2+发光至红光区域，研究反应过程及不同硅源、温度、氨气气流大小对产物结构和发光性能的影响；(2)对下一代红色荧光材料Sr[LiAl3N4]:Eu2+进行改性。通过优化合成条件和Eu2+掺杂浓度提高其发光效率；通过阳离子取代，调控Eu2+发光至600-630nm，进一步完善其发光性能。通过实施本项目，发展氮化工艺，研制新型红色发光材料，解决目前白光LED显色性指数和流明效率低的问题。

红色荧光粉是提高白光LED显色性指数和流明效率的关键，但能满足要求的红色荧光粉十分缺少。氮化物是目前性能较好的红色荧光粉，但存在合成成本高和发射光谱宽（红外溢出）的缺点，不利降低LED成本和提高其流明效率。本项目主要通过现有发光效率较高的氧化物黄色发光材料进行氮化和阳离子取代，以期实现其发光向长波长乃至红光区域的调制并得到新型红色荧光粉，为开发新的荧光粉做基础并提供思路，解决白光LED显色性指数和流明效率低的问题；同时也开展一些新型荧光粉研制工作，探索了其在测温、白光LED 和光伏领域的应用。. 在项目执行期间，取得一些重要研究成果，包括使用Si3N4代替SiO2合成黄色发光材料Li2SrSiO4-zNz：Eu2+，使其发光强度提高了30%；合成了一种非稀土掺杂的新型黄色荧光粉K2ZrSi2O7:Bi3+，通过时间分辨光谱和低温光谱证实了Bi3+在 K2ZrSi2O7中的占位和发光；研究了Yb3+-Er3+ 共掺Y7O6F9的上转换和下转换发光特性，结果表明在980nm 激光激发下，所得Y7O6F9:1%Er3+,5%Yb3+上转换发光强度是商用绿色荧光粉 β-NaYF4:2%Er3+,18%Yb3+ 发光强度1.8倍，展示这类材料光伏领域的重要应用前景；此外，研究表明Y7O6F9:1%Er3+还可以作为一种微型温度传感器测量芯片的温度；合成了两种绿色固态荧光碳点，量子效率分别为16%和30%，研究了他们在低功率白光LED 中的应用。. 在本项目的资助下，发表第一/通讯作者论文7篇(其中SCI 一区论文2篇，二区论文3篇）；作为项目负责人,申请到2018年兰州市城关区科技局项目1项，作为项目主要参与人员,申请到2019年度国家自然科学基金重点项目-促进海峡两岸科技合作联合基金项目。