Broadband far-red/near-infrared emission of Fe3+ and Mn4+ co-doped MgAl2O4 phosphors for plant lighting

Mn⁴⁺-activated phosphors are widely used in plant lighting due to their efficient far-red emission (600–760 nm). However, their narrow emission bandwidth limits their applications. To address this, we co-doped Fe³⁺ with a broadband far-red/near-infrared (NIR) emission (650–900 nm) with Mn⁴⁺ in a spinel-structured MgAl₂O₄ host. This strategy synergistically combines the luminescence characteristics of both ions to achieve a broadened spectral output. Upon 285 nm ultraviolet excitation, the Fe³⁺/Mn⁴⁺ co-doped MgAl₂O₄ system exhibits a dual-peak broadband emission spanning 600–900 nm, with emission maxima at 655 and 722 nm. Notably, the full width at half maximum (FWHM) reaches 132 nm, representing a 109% increase relative to the Mn⁴⁺ singly doped sample (FWHM = 63 nm). The dual-peak broadband emission is highly consistent with the absorption bands of the two types of phytochrome (Pr and Pfr). This spectral matching enables bidirectional control of the phytochrome photoconversion cycle. This work establishes an innovative strategy for developing broadband far-red phosphors that dynamically regulate phytochrome activity to advance precision plant lighting.