Dual-functional Cr3+-doped far-red to NIR broadband phosphors for high-fidelity white lighting and non-destructive detection

Abstract

Far-red to near-infrared (NIR) broadband phosphors are critical components in next-generation optoelectronics, enabling compact light sources for invisible non-destructive detection and addressing the red deficiency in high-fidelity lighting. In this study, a novel NIR phosphor LiGaTi_0.97Zr_0.03O₄:0.008Cr³⁺ (LGTZ:0.008Cr³⁺) was synthesized via substitution of Ti⁴⁺ with Zr⁴⁺ in LiGaTiO₄. The introduction of Zr⁴⁺ induces a lattice distortion, which not only enhances the photoluminescent quantum yield to 50.7% but also improves thermal stability, with emission intensity at 423 K retaining 67% of its room-temperature value. The phosphor exhibits an ultra-wide excitation band (290–510 nm) and broad far-red to NIR emission (650–1000 nm), peaking at 725 nm. This distinctive spectral profile arises from the synergistic effects of strong electron–phonon coupling (S = 5.71), cation-disorder-induced inhomogeneous broadening, and high ligand covalency (Racah parameter B = 598.6 cm⁻¹), which collectively enable its dual functionality. For non-destructive detection, a fabricated NIR pc-LED device demonstrates capability for deep-tissue biological imaging and internal fruit quality inspection. For high-fidelity white lighting, incorporating the LGTZ:Cr³⁺ phosphor into UV- and blue-pumped white pc-LEDs effectively bridges the far-red spectral gap. This yields warm white light with a low correlated color temperature (CCT = 3967 K for UV-pumped LED; 3400 K for blue-pumped LED) and an outstanding color rendering index (Ra, R9 = 94.5, 98 for UV-pumped LED; 93.8, 97 for blue-pumped LED), stable with increasing driving current. This work presents a strategy for versatile broadband phosphors, advancing the frontiers of both invisible sensing technologies and visible solid-state lighting.