Six- and five-coordinated Cr3+ in Ga2GeO5 invokes tunable broadband near-infrared emission toward night-vision applications

Broadband near-infrared (NIR) light sources play a critical role in widespread applications such as advanced spectroscopy analysis and nondestructive testing. One of the most promising techniques is the fabrication of broadband NIR phosphor-converted light emitting diode (pc-LED). However, the purposeful design of a tunable ultra-broadband NIR-emitting phosphor in a single host is still a challenge. In this work, Ga2GeO5 with two sites of six-coordinated [Ga1O(6)] and five-coordinated [Ga2O5] is chosen to host Cr3+, successfully producing tunable broadband NIR luminescence (680-1350 nm). It can be tuned largely from 828 to 970 nm with the full-width at half maximum (FWHM) varied from 208 to 258 nm just by simply adjusting the Cr3+-doping content. The tailoring of the Cr3+ NIR spectral emission is ascertained to the site occupation preference and competition. The encapsulation of a prototype of NIR pc-LED with an output power of 29.5 mW@390 mA is conducted for the implementation of night-vision application. This work provides a novel broadband NIR phosphor by Cr3+-doping in both the six- and five-coordination field, meanwhile, further demonstrating the feasibility of discovering new host material with more than one crystallographic site for Cr3+ to trigger tunable broadband NIR emission.