Ultra-efficient energy transfer and near-infrared luminescence in hexagonal aluminate phosphors enabled by heterogeneous ion pairs co-doping

Abstract

Near-infrared phosphor-converted light-emitting diodes have significant applications in biomedical imaging, night vision technology, industrial inspection, and spectral analysis. Typical phosphors, constituted with isolated Cr3+ ions and homogeneous Cr3+−Cr3+ ion pairs, represent the predominant strategy for facilitating efficient NIR emission. Nonetheless, this methodology requires extensive doping of Cr3+, leading to luminescent quenching and significant lattice distortion. Here, a heterogeneous ion pair (Mn2+-Cr3+) co-doping strategy was proposed to construct an ultra-efficient energy transfer from Mn2+ to Cr3+, and boost the NIR emission in trace Cr3+-doped hexagonal aluminate phosphors LaMgAl11O19:Cr3+. The formation of Mn2+-Cr3+ heterogeneous ion pairs was forecasted through in-depth structural and theoretical calculations and was then further demonstrated by electron paramagnetic resonance, X-ray photoelectron spectroscopy, and photoluminescence analysis. Notably, the Mn2+-Cr3+ heterogeneous ion pairs in LaMgAl11O19 could realize an ultimate energy transfer efficiency of 100%, resulting in a record NIR quantum efficiency (IQE~100%) in trace Cr3+ (0.5 mol%) doping. A high output power (134 mW@350 mA) NIR pc-LED and a high color rendering full-spectrum pc-LED (CRI = 90.0) were simultaneously realized based on LaMgAl11O19:Mn2+, Cr3+. This novel perspective on the heterogeneous ion pair offers an enriched understanding of the underlying design principles and facilitates the exploration of innovative NIR emitting phosphors.