Cr³⁺-Induced Structure Modulation and Near-Infrared Luminescence in Double Perovskite

Area of Science:

• Materials Science
• Solid State Physics
• Luminescence

Background:

• Lead-free halide double perovskites (DPs) are emerging as promising materials for near-infrared (NIR) phosphors.
• Chromium (Cr3+) doping offers tunable optical properties for these DPs.

Purpose of the Study:

• To investigate the luminescence properties of Cr3+-doped Cs2Ag0.6Na0.4In0.9Bi0.1Cl6 double perovskites.
• To elucidate the luminescence mechanisms and interactions between Cr3+ and self-trapped excitons (STEs).

Main Methods:

• Synthesis and characterization of Cr3+-doped lead-free halide double perovskites.
• Optical spectroscopy under different excitation wavelengths (405 nm and 808 nm).
• Analysis using Tanabe-Sugano diagrams and multivariate regression.
• First-principles calculations to understand electronic structure and luminescence pathways.

Main Results:

• The Cs2Ag0.6Na0.4In0.9Bi0.1Cl6:Cr3+ system exhibits dual-band luminescence (405 nm excitation) and NIR-only luminescence (808 nm excitation).
• Increasing Cr3+ concentration causes redshift and attenuation of STE luminescence, while Cr3+ luminescence shows a rise-then-fall trend.
• Tanabe-Sugano analysis indicates a weak crystal field and a spin-allowed 4T2 → 4A2 NIR transition for Cr3+.
• Cr3+ luminescence is partly attributed to self-absorption; first-principles calculations show Cr3+ suppresses STE luminescence by enhancing electron localization.

Conclusions:

• The study elucidates the distinct luminescence pathways of Cr3+ and STEs in lead-free halide double perovskites.
• Understanding the interaction dynamics provides insights for designing efficient NIR phosphors.
• The findings contribute to the development of novel optoelectronic materials.