Amplifying Upconversion by Engineering Interfacial Density of State in Sub-10 nm Colloidal Core/Shell Fluoride Nanoparticles

Abstract

Achieving bright photon upconversion under low irradiance is of great significance and finds many stimulating applications from photovoltaics to biophotonics. However, it remains a daunting challenge to significantly intensify upconversion luminescence in small nanoparticles with a simple structure. Herein, we report the amplification of photon upconversion through engineering interfacial density of states between the core and the shell layer in sub-10 nm colloidal rare-earth ions doped fluoride nanocrystals. Through tuning of the metal cations in the shell layer of alkaline-earth-based core/shell nanoparticles, both the interfacial phonon frequency and the density of state are evidently decreased, resulting in the luminescence intensification of up to 8224 times. The generality of this upconversion enhancement strategy has been verified through expansion of this approach to alkali-based core/shell nanoparticles. The engineering of photon density of state in such core/shell nanoparticles enables dynamic display and high-level security information storage.

Improved relative temperature sensitivity of over 10% K−1 in fluoride nanocrystals via engineering the interfacial layer

“…For the small NCs with large surface-to-volume ratio, the mass of activators is located on the surface; thus, engineering the surface phonon energy might further adjust the above negative TQE of Nd 3+ ions. 32 As shown in Fig. 2a, the XRD patterns verified that the as-prepared CaF 2 @SrYbF 5 :40Nd, SrF 2 @SrYbF 5 :40Nd and BaF 2 @SrYbF 5 :40Nd NCs were well assigned to cubic phases.…”

Manipulation of time-dependent multicolour evolution of X-ray excited afterglow in lanthanide-doped fluoride nanoparticles

“…In these systems, although the afterglow intensity decreases over time in contrast to photoluminescence which is stable, its output colour remains unchanged. Fluoride nanoparticles (NPs) with the characteristics of low phonon energy and high photostablity are superior for the incorporation of lanthanide ions with abundant ladder-like energy levels, which are broadly employed to generate upconversion (UC), downshifting (DS), and X-ray excited afterglow (XEA) emissions 31 – 35 . Thus, through constructing and editing core@shell architecture, a time-dependent multicolour evolution might be realized on demand.…”

NIR‐I‐Responsive Single‐Band Upconversion Emission through Energy Migration in Core–Shell–Shell Nanostructures

“…To verify our hypothesis, cubic NaYF 4 (α‐NaYF 4 ) is chosen as host lattice of core for Mn 2+ ions to avoid phase transformation (β→α) during synthesizing core‐multishell nanocrystals, [5c, 10c, 11] while CaF 2 and NaYbF 4 are selected as the epitaxial shell layer because of the ideal optical transparency, high crystallization and negligible lattice mismatch with α‐NaYF 4 (For α‐NaYF 4 , a =5.448 Å; for CaF 2 , a =5.451 Å; for α‐NaYbF 4 , a =5.415 Å) [12] . Typically, α‐NaYF 4 :Yb/Er/Mn nanocrystals were successfully prepared via a modified co‐precipitation method, and then used as core component for successive epitaxial growth of cubic CaF 2 interlayer and α‐NaYbF 4 outer shell through layer‐by‐layer growth strategy (Figure 3a).…”