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

Abstract

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 ≈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.