荧光粉
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荧光粉为一种固体材料,被深蓝光、紫外光或者电子束辐照后可以发出可见光。通过对荧光粉组份与结构的精细调节,可对发光光谱进行控制、以满足特定性能的需求。正因如此,在电子与照明行业(如显示行业、荧光灯以及白光LED领域)荧光粉被普遍使用。

大多数白光LED中都含有LED芯片(发出波长为440~470nm之间的蓝光)和荧光粉(黄粉、绿粉或/和红粉)涂层。荧光粉用以吸收部分LED芯片所发出的蓝光,而激发出的光再和其余穿过荧光粉的蓝光混合,就被人眼识别为白光。

白光LED的性能参数、包括长期可靠性都强烈地依赖于荧光粉材料的选择以及涂布的方式。商业上使用最广泛的黄色荧光粉在可见光波段500~700nm有宽的发光光谱,对蓝光(420~480nm)的吸收效果较高,化学与热稳定性优良。但是,此类黄色荧光粉的发射光谱在红光区缺乏,因此采用黄粉的白光LED通常是蓝白色调、相对色温的覆盖范围为4000~6500K。另外,此类LED通常不能满足最低显色指数方面的要求,而这一点对照明级LED至关重要。

最近,在红色荧光粉方面的最新进展可使暖白LED的相对色温值达到2700~4000K的范围,最低显色指数CRI可超过80。这些在颜色与显色性方面的进展使得白光LED相对于其他诸如白炽灯、卤素灯的传统光源更具竞争力。然而,因红色荧光粉发出光的很大部分波长都超过700nm(超过了人眼感知范围),所以相对于冷白LED来说,暖白的光效依然不高。通过使用更红的荧光粉材料,可使CRI超过90,但这样的代价是700nm以下的光输出会更少,LED总体光效也有下降。

为了保持在白光LED领域的领先地位,Lumileds将继续投入资源研发新型荧光粉材料。例如,最近开发出一款新颖的高性能、窄带宽的红光荧光粉材料,它可被蓝光高效率地激发(如图1),能使Lumileds生产出更高光效的LED,却不必在光品质、显色性方面进行折中。To maintain its leadership in white LEDs, Lumileds continues to invest in the research and development of new phosphor materials and manufacturing processes which result in higher quantum efficiencies and better lumen equivalent ratios. For example, recent research has focused on the synthesis of novel high-performance narrow-band red emitting phosphors, which can be efficiently excited by blue LEDs. Narrow band red phosphors enable even higher LED efficacies without compromising quality of light and color rendering (see Figure 1). The Nature article Narrow-band red-emitting Sr[LiAl3N4]:Eu2+ as a next-generation LED-phosphor material describes a particular class of narrow-band red phosphor materials which was recently developed by Lumileds. A prototype white LED, which included this particular class of red phosphors with a peak wavelength around 650nm and a FWHM of 50nm, resulted in an increase in luminous efficacy of 14% compared to commercially available high CRI LEDs.

除了开发创新的荧光粉材料之外,Lumileds也部署一个专门的团队开发新型的荧光粉涂布技术,此技术可以在大规模生产环境中使用,帮助降低成本并且最大化生产良率。