Ultrahigh Efficiency LiAlGa4O8: Cr3+, Ni2+ Near-Infrared Phosphor with an External Photoluminescence Quantum Yield Exceeding 70% via Cr3+–Ni2+ Energy Transfer

Ni2+-doped inorganic crystals are promising for generating broadband emissions from 1000 to 1700 nm, which are crucial for advancing NIR light sources. However, their commercial applications have been hindered due to their weak absorption. Herein, the LiAl5O8 crystal is present as the host for Cr3+ and Ni2+ ions due to its high density of available doping sites (Al3+) per unit volume (0.048/Å3) for Cr3+ sensitizers. By heavily increasing the doping concentration of Cr3+, an unprecedented broad emission band peaking at 773 nm emerges, enhancing the spectral overlap between the emission of Cr3+ and absorption of Ni2+, thus boosting the energy transfer efficiency from Cr3+ to Ni2+. This accelerated energy transfer rate competes favorably against nonradiative processes, allowing higher concentrations of Cr3+ without any photoluminescence quenching. Moreover, by substituting Ga3+ for Al3+, the excitation peak is successfully tuned from 405 to 445 nm, aligning perfectly with commercial blue diode chips. As a result, the optimal LiAlGa4O8: 0.26Cr3+, 0.1Ni2+ phosphor exhibits a broadband emission ranging from 950 to 1600 nm, achieving internal/external photoluminescence quantum yields up to 94.12 and 72.62%, respectively. The application demonstration of packaged lighting devices shows its great potential in the fields of poultry farming and life science.