Broadening and Enhancing the Emission of Phosphor Li₂MgTi₃O₈:Cr³⁺ by Cation Substitution

The portable near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) with a broad spectrum have great application potential in information encryption, infrared night vision, medical imaging, chemical component detection, nondestructive testing, and many other fields, in which stable and efficient ultrawide NIR-emitting phosphors have become a new pursuit. However, the low luminescence intensity and narrowband emission of most NIR phosphors limit their potential applications. Under this drive, a NIR-emitting phosphor, Li₂MgTi_2.99O₈:0.01Cr³⁺ (LMT:0.01Cr³⁺), with TiO₆ and MgO₆ octahedral sites for Cr³⁺, was developed. It exhibits 79.28% internal quantum efficiency (IQE) and a 155 nm full width at half maximum (fwhm) in the range of 600∼1300 nm. Based on the weakened crystal field strength through the [In³⁺-In³⁺] unit to cosubstitute the [Ti⁴⁺-Mg²⁺] unit, the emission peak red-shifted from 751 to 772 nm, with the fwhm widening to 205 nm in Li₂Mg_0.98In_0.04Ti_2.97O₈:0.01Cr³⁺phosphors (LMIT:0.01Cr³⁺). The IQE was also further enhanced to 85.02% by substituting Mg²⁺ in LMIT:0.01Cr³⁺ with Zn²⁺, increasing the index of lattice distortion at the luminescence center to get Li₂Mg_0.92In_0.04Zn_0.06Ti_2.97O₈:0.01Cr³⁺ (LMIZT:0.01Cr³⁺). NIR pc-LED devices were fabricated by combining LMIZT:0.01Cr³⁺ phosphor with a blue LED chip, and their potential applications were also evaluated, showing excellent prospects in NIR penetration imaging and information encryption.