Broadening and Enhancing the Emission of Phosphor Li<sub>2</sub>MgTi<sub>3</sub>O<sub>8</sub>:Cr<sup>3+</sup> by Cation Substitution
Ziyang Wu, Changheng Chen, Jinmeng Xiang, Jiwen Chang, Xiaoqi Zhao, Chongfeng Guo
Abstract
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, Li 2 MgTi 2.99 O 8:0.01Cr 3+ (LMT:0.01Cr 3+ ), with TiO 6 and MgO 6 octahedral sites for Cr 3+, 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 [In 3+ -In 3+ ] unit to cosubstitute the [Ti 4+ -Mg 2+ ] unit, the emission peak red-shifted from 751 to 772 nm, with the fwhm widening to 205 nm in Li 2 Mg 0.98 In 0.04 Ti 2.97 O 8:0.01Cr 3+ phosphors (LMIT:0.01Cr 3+ ). The IQE was also further enhanced to 85.02% by substituting Mg 2+ in LMIT:0.01Cr 3+ with Zn 2+, increasing the index of lattice distortion at the luminescence center to get Li 2 Mg 0.92 In 0.04 Zn 0.06 Ti 2.97 O 8:0.01Cr 3+ (LMIZT:0.01Cr 3+ ). NIR pc-LED devices were fabricated by combining LMIZT:0.01Cr 3+ phosphor with a blue LED chip, and their potential applications were also evaluated, showing excellent prospects in NIR penetration imaging and information encryption.