# Active Shell Engineering for Efficient Cascade Triplet Energy Transfer in Lanthanide Heterostructures

## TL;DR

This paper introduces a new method to enhance the performance of lanthanide nanoparticles by engineering their shells to improve energy transfer and emission efficiency.

## Contribution

The study presents a novel cascade triplet energy transfer mechanism using engineered active shells in lanthanide heterostructures.

## Key findings

- A 1200-fold emission enhancement was achieved with optimized shell thickness and ligand exchange.
- Near-unity triplet energy transfer efficiency was confirmed using Nd3+ as energy intermediates.
- The design overcomes surface quenching and weak absorption in traditional lanthanide nanoparticles.

## Abstract

Lanthanide‐doped nanoparticles (LnNPs) exhibit unique optical properties but suffer from severe surface quenching and weak absorption that fundamentally limit their performance. Here, we demonstrate a breakthrough cascade triplet energy transfer (TET) mechanism in precisely engineered NaYbF4@Ca0.8F2:Nd0.2@9‐anthracenecarboxylic acid (ACA) heterostructures. This core/active shell/organic molecule configuration combines both molecular sensitization with surface passivation, transforming conventional inert barriers into functional energy conduits. We explore in detail the synthetic conditions required to grow not just optimally active shells but also how best to assemble the organic ligands on the surface of core‐shell LnNPs. Systematic shell thickness optimization (0.8–4.6 nm) reveals an optimal shell thickness of ∼2.0 nm. When coupled with an appropriate ligand exchange strategy, we achieve a remarkable 1200‐fold emission enhancement compared to bare cores. Comprehensive spectroscopic investigations confirm near‐unity TET efficiency and reveal the cascade TET mechanism utilizing Nd3+ ions as energy intermediates to maximize the Yb3+ emission. Thus, our mechanism and heterostructure design present one of the most promising synthetic strategies to overcome the existing limitations of traditional LnNPs, establishing new paradigms for high‐performance heterostructures with broad applications in bioimaging, photon conversion, and optoelectronic devices.

Active shell engineering resolves the trade‐off between surface passivation and molecular sensitization in lanthanide nanoparticles. NaYbF4@Ca0.8F2:Nd0.2@ACA heterostructures transform inert shells into energy conduits, enabling cascade triplet transfer with near‐unity efficiency. Optimal shell thickness (∼2 nm) simultaneously achieves surface protection and efficient energy relay, establishing design paradigms for high‐performance luminescent materials.