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, Li2MgTi2.99O8:0.01Cr3+ (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 Li2Mg0.98In0.04Ti2.97O8:0.01Cr3+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 Li2Mg0.92In0.04Zn0.06Ti2.97O8:0.01Cr3+ (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.