Fabrication and optical properties of transparent ceramic persistent phosphors based on band-gap engineering

在2017财政年度，各种稀土铬掺杂石榴石(透明)陶瓷永久荧光粉被成功地开发出来，其发射波段从黄色到深红，甚至近红外(NIR)可调，用于新型WLED和生物医学应用。[1]以六种不同的Cr3+掺杂石榴石为例，介绍了如何基于Tanabe-Sugano(D3)图，利用Cr3+在深红区发射的晶场工程来设计有前途的永久荧光粉。如何选择合适的稀土离子作为共掺杂敏化剂，通过构建宿主参考结合能(HRBE)图来进一步提高Cr3+的持久发光性能。[2]利用Er3+和Cr3+共掺Y3Al2Ga3O12(YAGG：Er-Cr)永久荧光粉中两个不同陷阱深度的独立电子陷阱，Cr3+/Er3+Persl可以通过660 nm红光LED的光刺激原位充电，这是由于捕获的电子从深陷阱重新分布到浅陷阱。[3]选择GaGG：Ce-Pr-Cr作为候选材料，与商业蓝光LED(460 Nm)相结合，设计了一种具有增强显色指数(CRI)值的新型WLED器件。此外，这种WLED器件甚至可以作为持续发出黄色持续发光的荧光粉，在停止供电后持续几个小时。

In the fiscal year of 2017, various kinds of lanthanide-chromium doped garnet (transparent) ceramic persistent phosphors have been successfully developed with tunable emission bands from yellow to deep-red, even near-infrared (NIR) for new type wLED and biomedical applications.[1] Six different Cr3+ doped garnets were developed as a vivid example to introduce how to design promising persistent phosphors utilizing the “crystal field engineering” of Cr3+ emission in the deep-red region based on Tanabe-Sugano (d3) diagram, and how to choose proper lanthanide ions as co-doping sensitizers to further enhance the Cr3+ persistent luminescence by constructing the host referred binding energy (HRBE) diagram as a powerful theoretical prediction tool.[2] Utilizing two independent electron traps with two different trap depths in the Er3+ and Cr3+ co-doped Y3Al2Ga3O12 (YAGG:Er-Cr) persistent phosphor, the Cr3+/Er3+ PersL can be recharged in situ by photostimulation with 660 nm red LED thanks to the redistribution of trapped electrons from the deep trap to the shallow one. The results serve as a guide in developing promising NIR (>1000 nm) persistent phosphors used for long-term rechargeable optical imaging.[3] GAGG:Ce-Pr-Cr was chosen as the candidate material composition coupled with commercial blue LED (460 nm) to design a new type wLED device with an enhanced color rendering index (CRI) value. Furthermore, such kind of wLED devices can even act as persistent phosphors emitting yellow persistent luminescence continuously for several hours after stopping the power supply.