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

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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.