Nanocrystals of divalent europium-doped CsPbCl3 perovskites: a novel optoelectronic material with dual-emissions

Abstract

In the last five years, significant progress has been achieved in incorporating trivalent lanthanide (Ln³⁺) ions into CsPbX₃ halide perovskite nanocrystals (PeNCs), combining superior optoelectronic performance of semiconductors with abundant Ln³⁺: 4f–4f transitions. However, doping divalent europium (Eu²⁺) with parity-allowed 5d–4f transition inside CsPbX₃ remains unexplored. Herein, we develop a new class of dual-emitters based on Eu²⁺-doped CsPbCl₃ PeNCs. Narrowband violet emission and broadband orange emission assigned to the respective exciton recombination and Eu²⁺: 5d → 4f transition are concurrently observed. Steady/transient-state photoluminescence (PL) spectra, time-resolved PL (TRPL) spectra and femtosecond transient absorption (fs-TA) spectra evidence independent dual-emissions without exciton-to-Eu²⁺ energy transfer, which is attributed to the preferred location of Eu²⁺ on the surface of CsPbCl₃. As a consequence, exciton-longitudinal optical phonon interplay and surface ligand–Eu²⁺ coupling in the as-prepared Eu:CsPbCl₃ PeNCs are verified based on temperature-sensitive spectroscopic analyses, together with first-principles density functional theory (DFT) calculations and crystal-field calculations. These findings provide fundamental insights into the design of novel lanthanide-doped halide perovskite emitters for versatile optoelectronic applications.