Environmentally Friendly Fe ³⁺ -Activated Li ₂ MgTi ₃ O ₈ Far-Red Emitting Phosphors for Dual-Mode Optical Thermometry and Plant Growth Illumination

Fe 3+ -activated luminescent materials have recently evoked considerable interest owing to their environmentally friendly and versatile applications potential. In this study, novel Li 2 MgTi 3 O 8: Fe 3+ phosphors are synthesized and its luminescence properties were systematically investigated. The Li 2 MgTi 3 O 8: Fe 3+ phosphor exhibits a broad excitation spectrum covering the ultraviolet–visible region from 250 to 600 nm. Upon 417 nm excitation, the as-prepared phosphor shows a broad far-red emission band centered at 709 nm due to the 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transition of Fe 3+ ions, along with a good internal quantum efficiency (IQE) of 39%. Importantly, the emission band of phosphors can be well matched with the absorption spectra of plant pigments. Furthermore, the temperature sensing properties of the phosphor samples were analyzed by using the fluorescence intensity (FI) and fluorescence lifetime (FL) technique, achieving maximum relative sensitivities ( S r ) of 1.73% K –1 @423 K and 3.52% K –1 @373 K, respectively. These results indicate that Li 2 MgTi 3 O 8: Fe 3+ phosphors have potential applications for optical thermometry and plant growth illumination.