Chromium Ion Pair Luminescence: A Strategy in Broadband Near-Infrared Light-Emitting Diode Design

Area of Science:

• Materials Science
• Solid-State Chemistry
• Luminescence

Background:

• Portable near-infrared (NIR) light sources are crucial for spectroscopy, night vision, and bioimaging.
• Designing broadband NIR phosphors, especially those based on chromium (Cr³⁺) ion pairs, presents significant challenges due to isolated ion centers.

Purpose of the Study:

• To explore the solid-solution series SrAl_11.88-xGa_xO₁₉:0.12Cr³⁺ for NIR phosphors.
• To investigate structure-property relationships, focusing on the role of Cr³⁺-Cr³⁺ pairs and gallium incorporation.
• To evaluate the potential of these materials as next-generation NIR phosphor host systems.

Main Methods:

• Synthesis and characterization of the SrAl_11.88-xGa_xO₁₉:0.12Cr³⁺ solid-solution series.
• Crystallographic analysis to determine gallium incorporation sites within the magentoplumbite-type structure.
• Electron paramagnetic resonance (EPR) spectroscopy to identify isolated Cr³⁺ and Cr³⁺-Cr³⁺ pairs.
• Luminescence spectroscopy to analyze NIR emission properties and quantum efficiency.

Main Results:

• Gallium successfully incorporates into five distinct crystallographic sites within the magentoplumbite structure, influencing Cr³⁺-Cr³⁺ proximity.
• Broadband NIR luminescence (650-1050 nm) originates from Cr³⁺-Cr³⁺ pairs, with a peak emission between 740-820 nm.
• The optimized phosphor SrAl_5.88Ga₆O₁₉:0.12Cr³⁺ demonstrates high internal quantum efficiency (∼85%), radiant flux (∼95 mW), and excellent thermal stability (zero quenching up to 500 K).

Conclusions:

• Cr³⁺-Cr³⁺ pairs are key to achieving broadband NIR emission in this phosphor system.
• The magentoplumbite structure serves as a promising host for developing advanced NIR phosphors.
• This research advances the understanding of spectral shifts in phosphor solid solutions and their application potential.