Realizing intense deep-far-red broadband emission derived from mica ceramics through isomorphic cation substitution/doping for plant cultivation lighting and latent fingerprint identification

The exploration of transition metal Mn²⁺-activated luminescent materials is gaining increasing interests due to their diverse uses. Herein, Mn²⁺-incorporated fluorphlogopite (FP; KMg₃AlSi₃O₁₀F₂) mica ceramics were successfully prepared by a high-temperature solid-state reaction process, in which Mn²⁺ occupied the Mg²⁺ site through isomorphic substitution. The FP itself and derived Mn-mica (KMg_2.5Mn_0.5AlSi₃O₁₀F₂) possess negligible luminescence under ultraviolet (UV) excitation. However, the doping of rare earth Eu²⁺ into Mn-mica generates an evident deep-far-red broadband emission at approximately 620–860 nm, peaking at 720 nm when excited with 240–360 nm, which is ascribed to the intrinsic ⁴T₁ → ⁶A₁ transition of Mn²⁺, and the maximum spectral enhancement reaches approximately 22-fold when excited with 320 nm. The more dramatic result is that the complete substitution of Na⁺ for K⁺ in Mn-mica (NaMg_2.5Mn_0.5AlSi₃O₁₀F₂) not only results in an enlarged excitation range toward the near-UV region but also greatly enhances the deep-far-red emission (more than 12-fold) under 365 nm excitation. After optimization, the luminescence internal quantum yield (QY) is 87.4%, and the emission intensity at 423 K retains 78% of that at ambient temperature, indicating that the modified mica ceramics have superior luminescence and thermal stability through the cooperative effects of isomorphic cation substitution and doping, which is applicable for plant cultivation lighting and latent fingerprint identification.