Interstitial Zinc Boosted Light Tunability, Afterglow, and Ultrabright White Emission in Zinc Germanate (Zn2GeO4)

To reduce the burden of solid-state lighting and phosphor-converted light-emitting diode technologies on rare earth (RE) and avoid their potential supply risks, we have developed a RE-free Zn2GeO4 (ZGeO) microcrystalline phosphor. It was synthesized by a simple and scalable solid-state reaction of ZnO and GeO2 at 1200 degrees C. High-temperature synthesized ZGeO demonstrated color tunable emission from bluish-white to green on changing the excitation wavelength from 265 to 335 nm with a photoluminescence quantum yield of 42 and 9%, respectively. They could also convert highly energetic X-ray to bluish-green light emission. First-principles calculations showed that bluish-white and green light emissions are linked to zinc interstitials present, respectively, in zinc (Zni2) and zinc-germanium rings (Zni1). These defects generated in large numbers via high-temperature annealing along with antisites boosted the generation of trapping centers leading to dual persistent luminescence (PerL) of white and green light for more than 60 min as well as exhibited radioluminescence. Luminescent ink based on ZGeO was fabricated and successfully tested for anticounterfeiting applications. An extra effort has been vested on making this solid-state processed ZGeO dispersible in water-soluble deep eutectic solvent which could be a game changer for its marketability. This material has great potential to become an efficient RE and dopant-free phosphor synthesized by a simple, scalable, and cost-efficient route for applications in solid-state lighting, display, and anticounterfeiting, having multifunctionalities such as PerL, tunability, and RL.

Automated summary

To reduce the reliance on rare earth and avoid supply risks associated with solid-state lighting and phosphor-converted LED technologies, a RE-free Zn2GeO4 microcrystalline phosphor was developed. The phosphor exhibited color tunable emissions from bluish-white to green and could convert X-ray into bluish-green light emission. The material showed potential for usage in solid-state lighting, display, and anticounterfeiting applications due to its dual persistent luminescence, tunability, and radioluminescence.