Local Atomic Off-Centering Mediated Efficient Self-Trapped Excitonic Emission in Cs₅Cu₃Cl₆I₂ Nanoplates

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Low-dimensional metal halides, particularly copper(I)-based compounds, exhibit unique optoelectronic properties.
• These properties are linked to self-trapped excitons (STEs) causing intense, broad light emission.
• The precise crystal structure origins of STEs in these materials remain poorly understood.

Purpose of the Study:

• To elucidate the fundamental crystal structural origins of self-trapped excitons (STEs) in copper(I)-based low-dimensional metal halides.
• To synthesize and characterize novel Cs5Cu3Cl6I2 nanoplates (NPs) for investigating STE phenomena.
• To correlate local atomic structure with observed optoelectronic properties like intense broadband emission.

Main Methods:

• Synthesis of Cs5Cu3Cl6I2 nanoplates (NPs) via room temperature ligand-assisted reprecipitation.
• Photoluminescence (PL) spectroscopy, including temperature-dependent measurements, to analyze emission properties.
• Synchrotron X-ray pair distribution function (PDF) analysis to determine local atomic structure and off-centering.
• Sound velocity, Raman spectroscopy, and low-temperature heat capacity measurements to probe lattice dynamics.
• Single-particle fluorescence microscopy and super-resolution optical imaging to assess photostability and intermittency.

Main Results:

• Synthesized Cs5Cu3Cl6I2 NPs exhibiting intense blue emission, large Stokes shift, long lifetime, and high PLQY (~75%).
• Temperature-dependent studies revealed strong exciton-phonon coupling.
• Synchrotron X-ray PDF analysis confirmed local copper off-centering, indicating lattice anharmonicity and softness.
• Lattice softness and low-energy phonons were verified through complementary measurements.
• Single-particle imaging showed minimal intermittency and good photostability.

Conclusions:

• Local copper off-centering in Cs5Cu3Cl6I2 NPs is the key structural origin for intense STE-related broadband emission.
• The soft lattice structure and associated low-energy phonons facilitate the formation and stabilization of STEs.
• These findings provide crucial insights into the mechanism of light emission in copper(I)-based metal halides.
• The characterized Cs5Cu3Cl6I2 NPs demonstrate potential for optoelectronic applications due to their emission properties and stability.