Non-Rare-Earth Na₃AlF₆:Cr³⁺ Phosphors for Far-Red Light-Emitting Diodes

Emerging phototherapy in a clinic and plant photomorphogenesis call for efficient red/far-red light resources to target and/or actuate the interaction of light and living organisms. Rare-earth-doped phosphors are generally promising candidates for efficient light-emitting diodes but still bear lower quantum yield for the far-red components, potential supply risks, and high-cost issues. Thus, the design and preparation of efficient non-rare-earth activated phosphors becomes extremely important and arouses great interest. Fabrication of Cr³⁺-doped Na₃AlF₆ phosphors significantly promotes the potential applications by efficiently converting blue excitation light of a commercial InGaN chip to far-red broadband emission in the 640-850 nm region. The action response of phototherapy (∼667-683 nm; ∼750-772 nm) and that of photomorphogenesis (∼700-760 nm) are well overlapped. Based on the temperature-dependent steady luminescence and time-resolved spectroscopies, energy transfer models are rationally established by means of the configurational coordinate diagram of Cr³⁺ ions. An optimal sample of Na₃AlF₆:60% Cr³⁺ phosphor generates a notable QY of 75 ± 5%. Additionally, an InGaN LED device encapsulated by using Na₃AlF₆:60% Cr³⁺ phosphor was fabricated. The current exploration will pave a promising way to engineer non-rare-earth activated optoelectronic devices for all kinds of photobiological applications.