Cr³⁺?Fe³⁺ Energy Transfer Offset Enabling Anti-Thermal Quenching Near-Infrared Emission for Coded Wireless-Communication Applications

Broadband near-infrared (NIR) emission phosphors are crucial for the construction of next-generation smart lighting sources; however, the thermal quenching (TQ) issue poses a significant challenge to their applications. In this study, anti-TQ NIR emission is demonstrated in hexafluoride phosphors, using a facile Cr3+/Fe3+ co-doping strategy. Owing to the controlled forward resonance energy transfer (ET) from Cr3+ to Fe3+ and one-phonon-assisted back ET from Fe3+ to Cr3+, the thermally enhanced broadband NIR luminescence is realised in series of fluoride such as Na3FeF6:Cr3+, Na3GaF6:Cr3+, Fe3+, K2NaScF6:Cr3+, Fe3+, etc. By varying the chemical composition of the phosphor, the anti-TQ emission is achieved even upon raising the temperature to approximate to 423 K. The anti-TQ luminescence mechanism is investigated, and the ET offset effect on luminescence TQ is demonstrated. More importantly, by combining these phosphors with blue InGaN chip, anti-/zero-TQ NIR light emitting diodes with a high photoelectric conversion efficiency even up to 19.13%@20 mA are further fabricated to realize the emerging coded optical wireless-communication applications. These findings can initiate the exploration of NIR phosphors with anti-TQ luminescence properties for advanced optoelectronic applications.