Persistent luminescence (PersL) materials, generally rare earth- or transition metal- doped crystalline matrices, are uncommon phosphors able to temporarily store optical energy, leading to unique delayed and long-lasting luminescence, so-called afterglow. PersL phosphors, typically microsized powders dispersed in resins or inks, are now being commercially used for design, night security and road marking purposes. However, the relatively low storage capacity of PersL phosphors hurdles their potential use for emerging applications, being the development of transparent PersL materials that enable more efficient energy storage highly demanded. Also, several relevant scientific fields such as anticounterfeitings, illumination or data storage would clearly benefit from the development of PersL optical quality coatings.[1,2]

In general, wet deposition of nanoparticles is a recognized way to prepare scattering-free films.[3] However, in case of PersL phosphors, this method suffers from the difficulty to prepare colloidally stable particles featuring sufficiently high crystalline quality as to demonstrate efficient properties. To overcome this issue, we propose to develop few nanometer-thick nanostructured garnet-based films following a monolithic sol-gel route. After sol-gel reaction, deposition and controlled thermal annealing, we demonstrate transparent garnet films featuring efficient green emission and afterglow. We prove the versatility of our method by changing the garnet composition to reach films with distinct PersL kinetics and chromaticity. Due to the transparency of films and their unique optical properties, we prove chameleon-like time-dependent chromaticity of garnet stacks.

Our elaboration approach opens an avenue towards the conception of efficient PersL coatings and the unique chameleon-like property offers promising opportunities for PersL nanophosphor applications such as anticounterfeiting tags.

References:

[1] Castaing, V. et al.; Journal of Applied Physics 2021, 130 (8), 080902.

[2] Castaing, V. et al.; J. Phys. Chem. C 2021, 125 (18), 10110–10120.

[3] Arroyo, E. et al.; J. Mater. Chem. C 2021, 9 (13), 4474–4485.