染料包埋的核壳结构YAG:Ce3+/SiO2荧光粉的制备与发光性能研究

Phosphors-converted white LED, based on blue GaN chips, is expected to become the next generation of lighting source. Aiming at preparing warm white LED, it is desirable to develop a new type of highly efficient, full color white-emitting phosphors based on blue LED chips. The white LED technique involving yellow YAG:Ce3+ converted phosphors was developed earliest, and is currently the ripest one, however, its red emission is not enough, as a consequence, the converted white light has low color-rendering index. This project aims to develop an unblended single LED phosphors with rich red emission, which will select YAG:Ce3+ as a mother material and then prepare the core/shell hybrid composite (YAG:Ce3+@dyes@SiO2) via SiO2 coating and simulatneous embedding of fluorescent dyes such as Rhodamine and Indodicarbocyanine. Fluorescent dyes are employed to convert partly the green and yellow irradiations emitted by YAG:Ce3+ core and produce the broadband red-rich emissions; It is expected to get one kind of dye-embeded core (YAG:Ce3+)/shell (SiO2) hybrid phosphors with red-rich emissions as well as high stability against photo-irradiating and heating, and with good compatibility to current LED technique commercially available. Such phosphors will be encapsulated for warm white LED. For easier surface coating, an appropriate solution-processed method will be developed to synthesize nearly spherical YAG:Ce3+ phosphors with submicrometer size and bright luminescence. Some definite experimental methods and conditions need to be explored for controlled surface coating and embedding of organic dyes on both the small-sized laboratory-available and big-sized commercially available YAG:Ce3+ phosphors; As well, effective doping concentration of dyes and optimum thickness of outer shell of SiO2 against the luminescence bleaching induced by photo-irradiating and heating need to be explored. This project is expected to provide experimental evidences for preparing blue-LED-based yellow phosphors for high color rendering index and full color white light.

基于蓝光GaN芯片的荧光粉转换的白光LED可望成为下一代照明光源。为制备暖白光LED，亟待开发新型全色白光荧光粉。以黄光YAG:Ce为转换荧光粉的白光LED技术是发展最成熟的一种, 但其红光成分不足，显色性差；本项目拟以其为基体进行SiO2表面包覆，同时包埋染料罗丹明、碳菁素等，研制一种非混合型、红色成分丰富的核壳杂化单一荧光粉；用染料转换部分内核黄绿光而产生宽带红光，获得与现行商用LED技术兼容性较好且有丰富红光发射和较高光热稳定性的YAG:Ce核/SiO2壳杂化荧光粉，并封装白光LED；拟选择合适的湿化学方法制备亚微米尺度，发光效率高，易于表面包覆的近球形YAG:Ce荧光粉。探索实验方法和条件实现对湿法制备的小尺寸和商用大尺寸的YAG:Ce荧光粉的可控包覆和染料包埋，探索有效的染料嵌入浓度和抑制染料因光辐照和加热而漂白的最佳壳层厚度，为蓝光LED用高显色性白光荧光粉的开发提供实验依据。

基于蓝光GaN芯片的荧光粉转换的白光LED可望成为下一代照明光源。为制备暖白光LED，亟待开发新型全色白光荧光粉。以黄光YAG:Ce为转换荧光粉的白光LED技术是发展最成熟的一种, 但其红光成分不足，显色性差，有待改善。本项目尝试了多种湿化学方法（共沉淀、均匀沉淀、类微乳液和溶剂热法）和路径来制备亚微米尺度，发光效率高，易于表面包覆的近球形YAG:Ce黄色荧光粉。其中，溶剂热法是一种有效的方法。所制备的球形颗粒是由尺寸较小的纳米晶自组装而成，粉体尺寸在0.1~2.0 μm范围内可调控。溶剂热法制备的YAG:Ce较商用粉有较宽的激发范围，还可用于近紫外LED芯片激发，量子效率达到~30%。选择吸收黄绿光而发射红光的商用染料Rho101-NHS ester，探索到了相应的实验方法和条件，实现对溶剂热制备的小尺寸和商用大尺寸的YAG:Ce荧光粉的可控表面SiO2包覆和染料包埋，剪裁了YAG:Ce内核的发光，显著增加了红光发射成分。确定了染料嵌入浓度和较好的壳层厚度。研制出了一种非混合型、红色成分丰富的核壳杂化单一荧光粉。发光动力学研究表明外壳中的染料分子是由再吸收过程获得内核YAG:Ce的能量而产生红光发射。对比研究了粉末聚集与分散状态下的发光性质，发现外层染料再吸收过程存在距离效应，存在某一临界距离，近程激发无效，大于临界距离的远程激发更有效。分散状态下表层染料再吸收效应微弱，Ce的发射没有有效地被外层染料所吸收。这种激发距离决定的再吸收过程的实验发现在国际上尚属首次。研究了溶剂热制备及商用YAG:Ce3+荧光粉在表面修饰前后的发光热稳定性，溶剂热法制备YAG:Ce热稳定较差，有待进一步改善，光辐照是造成发光猝灭的更重要因素。外壳层中的染料具有较高的光热稳定。将所制备的荧光粉与蓝光芯片封装，制备出了高显色性白光LED。溶剂热制备的YAG:Ce经SiO2包覆和染料包埋后显色指数显著提到到91，流明效率也达到73 lm/W，色温低至4028 K。商用粉经表面修饰后，显色指数达到80，流明效率在200 lm/W以上。本研究为蓝光LED用高显色性白光荧光粉的开发提供了新的实验路径和依据，具有一定的研究意义。