单一自激活基质白光荧光材料的高通量优选及光谱调控机制研究

White light emitting diode (LED) has become the new generation energy efficient lighting technique, and employing UV LEDs coated with single-phase white light emitting phosphors has become one of the development trends of the white LED. The lighting of self-activated substrate can be used as an important part of single-phase white light emitting phosphors, so the single-phase self-activation based white light emitting phosphors have great potentialities. This work focuses on the research of Na2TiSiO5 and Li2MnO3 with the potential to become the single-phase self-activation based white light emitting phosphors. (1) Na2TiSiO5 emits a broad band white light close to ideal white light, but the white light of Na2TiSiO5 is visually harsh and cold. The visually harsh and cold problem of Na2TiSiO5 can be solved in two ways to obtain ideal white light: band gap engineering and high throughput screening the doping ions (such as Mn2+, Eu3+, Cr3+) that can emit red light in Na2TiSiO5. (2) Red phosphors always restrict white LED’s further development. Li2MnO3 not only emits red light, but also the emission is tunable in red-yellow-green region when Li2MnO3 is excited at different wavelengths. The key priority is using high throughput screening technology to optimize the doping ions (such as Ce3+, Eu2+, Bi3+) that can emit broad band blue-violet light in Li2MnO3. Then using energy transfer mechanism regulates the spectrum to obtain white light in Li2MnO3. (3) By systematically studying the two kinds of materials, the physical mechanisms of structure character, band gap engineering, mixing of spectrum and energy transfer in tuning the spectrum will be discovered.

白光LED是新一代节能环保光源，紫外芯片结合单一基质白光荧光材料实现白光是其发展趋势之一。自激活基质本身的发光可以作为单一基质白光的重要组成部分，因此单一自激活基质白光荧光材料具有良好发展潜力。本项目聚焦于具有单一自激活基质白光荧光材料基本特性潜质的Na2TiSiO5和Li2MnO3的研究。(1)Na2TiSiO5的宽谱发光非常接近理想白光，但发光偏冷。从能带调控和高通量优选发红光的掺杂离子两方面改善Na2TiSiO5的发光偏冷问题以获得理想白光。(2)红色荧光材料一直制约着白光LED的发展，Li2MnO3不仅可以发射红光，而且不同波长光激发下发光可绿-黄-红调节。重点采用高通量系统优选在Li2MnO3中发宽谱蓝紫光的掺杂离子，同时通过能量传递等调控光谱以获得白光。(3)通过两类材料的系统研究，揭示单一自激活基质白光荧光材料的结构特征、能带调控、光谱复合、能量传递等对光谱调控的物理机制。

本项目主要聚焦于节能环保白光LED用直接发射白光荧光材料的研究。一方面，基于三基色原理，设计、制备了Ce3+单掺，Eu3+（红）、Bi3+（蓝）、Tb3+（绿）单掺、共掺或三掺的光谱可调控紫外激发白光荧光材料。Ca2.83-yZrSi2O9:0.17Eu3+,yBi3+在紫外光激发下，同时发射源于Bi3+离子的宽带谱蓝光和Eu3+离子的红光，Bi3+的共掺显著增强了Eu3+的发光强度，存在Bi3+到Eu3+的能量传递。Ca2.74-zZrSi2O9:0.17Eu3+,0.09Bi3+,zTb3+在紫外光激发下，同时发射源于Bi3+离子的宽带谱蓝光、Tb3+离子的绿光和Eu3+离子的红光，存在Bi3+到Tb3+的能量传递。随着Tb3+掺杂浓度z的增加，Ca2.74-zZrSi2O9:0.17Eu3+,0.09Bi3+,zTb3+的色坐标由粉橙区域逐渐移动到白光区域，Tb3+的引入进一步有效调控了发光光谱。另一方面，基于Eu2+和Eu3+离子均可以作为发光激活离子的基础，设计、制备了混价Eu离子掺杂的光谱可调控紫外激发白光荧光材料。Ba1-xZrSi3O9:xEu(x=0.15)中Eu2+和Eu3+离子的荧光量子效率较高，在355、392nm波长紫外光激发下荧光量子效率分别为65.8%、94.8%。随着Eu离子掺杂浓度x的变化，Ba1-xZrSi3O9:xEu的发光颜色可以在蓝、粉、白区域调控，甚至Ba1-xZrSi3O9:xEu(x=0.15)可以在多波段紫外光(392、260、180nm)激发下直接发射白光。Ba1-xZrSi3O9:xEu的荧光高温热稳定性也较好，150℃时Ba1-xZrSi3O9:xEu(x=0.15)的发光强度仍保持有室温发光强度的96%(λex=392nm)。另外，拓展了混价Eu离子掺杂的荧光材料在光信息存储方面的应用。Eu离子的掺杂在BaZrSi3O9中引入了位于导带底以下0.90eV附近的深陷阱，而且BaZrSi3O9:Eu中的陷阱分布是可以调控的。空气氛围制备的样品在还原气氛退火后，深陷阱浓度增强，同时样品颜色加深，还原气氛制备的样品在空气氛围退火后，深陷阱浓度显著降低，同时样品颜色由黄色变回白色。实验结果表明，深陷阱源于氧空位。第一性原理计算进一步表明深陷阱源于层间的VO1空位。