Site-selective occupation of Cr3+ ions toward ultra-broadband near-infrared emission stannate phosphors

Abstract

Cr3+-activated near-infrared (NIR) luminescent materials with broadband emission have attracted extensive attentions for multipurpose NIR phosphor-converted light-emitting diodes (LED). It is widely believed that broadband NIR-emitting from optical center Cr3+ could merely made in crystal-filed caused six-coordinated sites or four-coordinated sites. Herein, taking La3Ga5SnO14 compound with six-coordinated Sn and four-coordinated Ga sites as host, we design and synthesize a new ultra-broad NIR-emitting La3Ga5Sn1-xO14:xCr3+ (LGSn1-x:xCr3+) phosphor ranging from 700 to 1500 nm via solid-state reaction. Structural analysis, low-temperature spectra investigations, and density functional theory calculations demonstrate that, in La3Ga5SnO14 (LGSn) host lattice, six-coordinated Sn sites and four-coordinated Ga sites can be successfully occupied by Cr3+ ions, leading to two distinct Cr3+ centers and an impressive broadband with full width at half maximum of up to 275 nm. At 373 K, emission intensity of LGSn0.97:3%Cr3+ phosphor maintains 43% of that at room temperature. We fabricate a NIR phosphor-converted LED device by using as-prepared LGSn0.97:3%Cr3+ phosphor and a blue LED chip and demonstrate its potential applications in night vision and food analysis. These findings provide not only an in-deep insight on site-occupation of Cr3+ residing in compounds with six-coordinated sites and four-coordinated sites but also feasible method of designing ultra-broadband NIR phosphors.