Rare‐Metal‐Free Ultrabroadband Near‐Infrared Phosphors
Guojun Zheng, Chenjie Lou, Zeyue Yuan, Wenge Xiao, Longbing Shang, Jiyou Zhong, Mingxue Tang, Jianrong Qiu
Abstract
Abstract Trivalent chromium (Cr 3+ ) is an attractive near‐infrared (NIR) emitter, but its ultrabroadband NIR emission is limited to host crystals containing large amounts of rare‐metal elements and usually suffers from low internal quantum efficiency (IQE) and poor thermal stability. Here, a class of high‐performance, rare‐metal‐free ultrabroadband NIR phosphors, are reported by revealing that weak‐field Cr 3+ centers featuring broadband NIR emission with near‐unity IQEs are intrinsic, though in trace quantities, to Cr 3+ doped MgAl 2 O 4 spinel (MAS) and its derivatives well‐known for their narrowband far‐red emission. It is shown that such weak‐field Cr 3+ centers stem from cation inversion ubiquitous in spinel compounds, and their quantity can be increased simply by superstoichiometric Al 2 O 3 /Ga 2 O 3 . Then SiO 2 is introduced into Al 2 O 3 ‐excess MAS to break the inversion symmetry of Cr 3+ centers for greatly improving the probabilities of their otherwise parity‐forbidden 3 d –3 d transitions. The as‐fabricated phosphor‐converted light‐emitting diodes are capable of emitting ultrabroadband NIR light with high photoelectric efficiency (16.0%) and optical power (180.8 mW), and excellent spectral stability, which apparently outperforms existing state‐of‐the‐art devices.