# Lanthanide-Doped Cs2ZrCl6 Perovskite Nanocrystals for Multimode Anti-Counterfeiting Application

## TL;DR

Researchers developed lanthanide-doped nanocrystals that emit different colors under various light sources, creating a secure anti-counterfeiting material.

## Contribution

A new colloidal synthesis method for lanthanide-doped Cs2ZrCl6 nanocrystals with excitation-dependent multimode luminescence.

## Key findings

- Nanocrystals show efficient energy transfer from self-trapped excitons to lanthanide ions.
- Tb3+ and Eu3+ enable distinct excitation pathways bypassing STE emission.
- Triple-mode anti-counterfeiting labels were fabricated using these nanocrystals.

## Abstract

The escalating prevalence of counterfeiting and forgery has imposed unprecedented demands on advanced anti-counterfeiting technologies. Traditional luminescent materials, relying on single-mode or static emission, are inherently vulnerable to replication using commercially available phosphors or simple spectral blending. Multimode luminescent materials exhibiting excitation wavelength-dependent emission offer significantly higher encoding capacity and forgery resistance. Herein, we report the colloidal synthesis of lanthanide-doped Cs2ZrCl6 nanocrystals (Ln3+ = Tb, Eu, Pr, Sm, Dy, Ho) via a robust hot-injection route. These nanocrystals universally exhibit efficient host-to-guest energy transfer from self-trapped excitons (STEs) under 254 nm, yielding sharp characteristic Ln3+ f–f emission alongside the intrinsic broadband STE luminescence. Critically, Tb3+ enables direct 4f → 5d excitation at ~275 nm, while Eu3+ introduces a low-energy Eu3+ ← Cl− LMCT band at ~305 nm, completely bypassing STE emission. Due to their multimode luminescent characteristics, we fabricate a triple-mode anti-counterfeiting label displaying different colors under different types of excitation. These findings establish a breakthrough excitation-encoded multimode platform, offering potential applications for next-generation photonic security labels, scintillation detectors, and solid-state lighting applications.