Atomic layer deposition (ALD) of nanoscale coatings on SrAl₂O₄‐based phosphor powders to prevent aqueous degradation

Abstract

The aqueous degradation of Eu2+‐activated and Dy3+‐codoped strontium aluminate (SrAl2O4:Eu2+, Dy3+, SA2‐Green) long afterglow phosphors synthesized from solid‐state reaction and coated with nanoscale metal oxide protective layers (≤12 nm) via atomic layer deposition (ALD) is investigated. Uncoated phosphor powders degrade rapidly upon water immersion and lose their green phosphorescence within 48 hours of water exposure. Postmortem investigations reveal hydration and decomposition of the SrAl2O4 phase. ALD of ~10 nm Al2O3 or ~12 nm TiO2 is found to significantly improve the powder's resistance to aqueous degradation. All ALD‐coated powders show minimal structural and chemical degradation and retain phosphoresence after 48 hours of water immersion. This enhanced durability offers a new pathway for applying long afterglow phosphors to outdoor applications like roadway markings or safety signage and for their incorporation into more eco‐friendly waterborne coatings.

Persistent luminescence of transparent ZnGa2O4:Cr3+ thin films from colloidal nanoparticles of tunable size

“…To overcome these drawbacks, films based on persistent phosphors (mainly green emitting SrAl 2 O 4 :Eu 2+ ,Dy 3+ ) have been also reported. 11,12,13,14,15 Chromium doped zinc gallate (ZnGa 2 O 4 :Cr) is another persistent phosphor with emission located in the red to near infrared (NIR) region. Zinc gallate shows cubic spinel structure.…”

Surface modification and functionalization of powder materials by atomic layer deposition: a review

“…With the ALD TiO 2 coating, the uoride particles obtained enhanced adhesion with the hydrophobic shells and their chemical stability towards moisture was remarkably improved. In addition, for SrAl 2 O 4 -based long aerglow phosphor particles, the aqueous durability can be signicantly improved by depositing nanoscale ALD Al 2 O 3 or TiO 2 layers, as reported by Karacaoglu et al 32 In recent years powder ALD has shown potential in the eld of nuclear energy. The precise processing ability and the relatively low deposition temperature are the key advantages of ALD for future applications in nuclear energy eld.…”

Synthesis and Characterization of CaAl2O4: Dy3+ and CaAl2O4: Sm3+ Phosphor Powders

“…Considering these results, it was necessary to add H 3 BO 3 to this system to reduce the reaction temperature and shorten the process. In addition, it has been revealed in previous studies that boric acid contributes positively to the luminescence characteristic and provides an improvement in the luminous intensity[1,9].…”

“…These features make them beneficial in many applications, such as luminous paints in buildings, factories, highway, ceramics, airport, and, in glow watches, escape and warning signs, and the textiles. Moreover, phosphors have been used as efficient materials for generating assorted emission colors in the process up to the present which have many applications in display devices and solid-state lighting, etc [1][2][3].…”