Surface crystallization enhanced upconversion luminescence in NaGdF4:Yb,Er@NaYF4 core/shell nanocrystals

Coating upconversion nanocrystals with an inert shell for removing surface defects is confirmed to be an efficient way for remarkably enhancing upconversion luminescence. However, it is not clear whether surface atomic structures on the outer inert shell affect upconversion luminescence of active cores. Here, we improved the surface crystallinity of NaGdF4:Yb,Er@NaYF4 active-core/inert-shell nanocrystals using ultrasonic oscillation. It was observed that surface crystallization of the inert shell could lead to an obvious enhancement in upconversion luminescence. The improved surface crystallinity has no obvious influence on the electronic transition in upconversion luminescence processes, but decrease the scattering and absorption to excitation and emission photons. This result clearly indicates that surface crystallization of the inert shell is a powerful route for further enhancing upconversion luminescence besides of the concept of core/shell structure.

Automated summary

Coating upconversion nanocrystals with an inert shell has been proven to effectively enhance upconversion luminescence. This study focuses on the effect of surface atomic structures on the upconversion luminescence of active cores. By improving the surface crystallinity of the inert shell, the researchers found a significant enhancement in upconversion luminescence. The improved surface crystallinity did not affect electronic transitions, but reduced scattering and absorption of excitation and emission photons.