Sub-6 nm monodisperse hexagonal core/shell NaGdF4 nanocrystals with enhanced upconversion photoluminescence

Jing Liu; Guanying Chen; Shuwei Hao; Chunhui Yang

doi:10.1039/c6nr08675f

Sub-6 nm monodisperse hexagonal core/shell NaGdF₄ nanocrystals with enhanced upconversion photoluminescence

Nanoscale. 2017 Jan 7;9(1):91-98. doi: 10.1039/c6nr08675f. Epub 2016 Dec 8.

Authors

Jing Liu¹, Guanying Chen, Shuwei Hao, Chunhui Yang

Affiliation

¹ MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China. chenguanying@hit.edu.cn yangchh@hit.edu.cn.

PMID: 27929179
DOI: 10.1039/c6nr08675f

Abstract

The ability to fabricate lanthanide-doped upconversion nanocrystals (UCNCs) with tailored size and emission profile has fuelled their uses in a broad spectrum of biological applications. Yet, limited success has been met in the preparation of sub-6 nm UCNCs with efficient upconversion photoluminescence (UCPL), which enable high contrast optical bioimaging with minimized adverse biological effects entailed by size-induced rapid clearance from the body. Here, we present a simple and reproducible approach to synthesize a set of monodispersed hexagonal-phase core NaGdF₄:Yb/Ln (Ln = Er, Ho, Tm) of ∼3-4 nm and core/shell NaGdF₄:Yb/Ln@NaGdF₄ (Ln = Er, Ho, Tm) UCNCs of ∼5-6 nm. We show that the core/shell UCNCs can be up to ∼1000 times more efficient than the corresponding core UCNCs due to the effective suppression of surface-related quenching effects for the core. The observation of prolonged PL lifetime for the core/shell than that for the core UCNCs demonstrates the role of the inert shell layer for the protection of the core. The achievement of sub-6 nm NaGdF₄ UCNCs with significantly improved luminescence efficiency constitutes a solid step towards high contrast UCPL optical imaging with secured biological safety.