Cr3+-Cr3+ Pairing and Multi-Site Engineering in Sr2ZnAl22O36 phosphor for Broadband Near-Infrared Emission

Abstract

Cr3+-activated phosphors are advancing near-infrared (NIR) technology, offering broadband emissions crucial for bioimaging, night vision, and optical communication. In the present study, we introduce a novel Sr2ZnAl22O36: xCr3+ (SZAO) phosphor, designed for enhanced luminescence and thermal stability. X-ray powder diffraction (XRD) and Rietveld refinement confirmed its phase purity, while bond valence sum, and bond energy calculations provided insights into Cr3+ ion incorporation. Electron paramagnetic resonance (EPR) and photoluminescence (PL) studies revealed site-dependent emissions, with sharp 2E → 4A2 transitions from isolated Cr3+ ions and broad 4T2 → 4A2 transitions from Cr3+-Cr3+ pairs, generating a broadband NIR emission (650–900 nm). Notably, the phosphor retained 69.9% of its emission intensity at 423 K to that of at the room-temperature, demonstrating strong thermal stability. Fluorine doping further improved performance, reducing thermal quenching from 32% to 19% and increasing the activation energy barrier to 0.27 eV. To demonstrate its practical application, we fabricated an NIR phosphor-converted LED (pc-LED), verifying its strong performance. These findings establish SZAO: Cr3+ as a high-performance NIR phosphor with excellent emission properties and thermal resilience. With its optimized design, this material lays the foundation for next-generation NIR pc-LEDs.