Energy transfer-induced blue light-excited broadband near-infrared luminescence in fluoride Na3AlF6:Mn4+,Fe3+

Abstract

The transition metal ion Fe³⁺ serves as an environmentally friendly and chemically stable activator for near infrared (NIR) light, whereas the intrinsic property of no efficient absorption in the blue light (440–460 nm) region poses a challenge for its applications. Herein, blue light-excited Fe³⁺-NIR broadband emission is demonstrated in Na₃AlF₆:Mn⁴⁺,Fe³⁺via a facile and general Mn⁴⁺ → Fe³⁺ energy transfer (ET) strategy. Under 463 nm blue-light excitation, in addition to typical narrowband red emission from Mn⁴⁺, a broadband NIR emission centered at 826 nm with a full width at half maximum (FWHM) of 127 nm from Fe³⁺ was achieved using this phosphor. Photoluminescence dynamics characterization and theoretical simulations reveal that Mn⁴⁺ → Fe³⁺ belongs to a resonant ET process dominated by electric dipole–dipole interactions. Additionally, this approach can also be extended to other fluorides, such as K₂NaAlF₆:Mn⁴⁺,Fe³⁺, confirming its universality. An NIR phosphor converted light-emitting diode was fabricated by combining the phosphor Na₃AlF₆:Mn⁴⁺,Fe³⁺ with a 450 nm blue chip, showing applications in night vision imaging and other fields. This study also provides new insights into the exploration of Fe³⁺-doped NIR materials with strong blue light absorption.