image: Figure | Morphology and structure of MgO:Ni2+,Cr3+ translucent ceramics.a Images of polished MgO:x%Ni2+,y%Cr3+ (x = 0-0.7, y = 0 and 0.3) ceramics under natural light. b The SEM image of MgO:0.3%Ni2+,0.3%Cr3+ ceramic and the left bottom inset shows the histogram of grain size distribution. c The TEM image of MgO:0.3%Ni2+,0.3%Cr3+ ceramic and the right top inset shows the enlarged part of lattice fringe marked in red square. d The SAED of MgO:0.3%Ni2+,0.3%Cr3+ ceramic.
Credit: Simin Gu et al.
Near-infrared (NIR) light sources have revolutionized multiple fields including biomedical imaging, material analysis, and security screening through their non-destructive detection capabilities. While traditional incandescent sources suffer from low efficiency and bulkiness, phosphor-converted LEDs (pc-LEDs) initially emerged as compact alternatives. However, three fundamental limitations persist: inherent LED efficiency droop, phosphor thermal degradation and poor thermal conductivity (~0.5 W·m-1·K-1) of organic binders. These challenges have propelled the development of near-infrared luminescent ceramic-converted laser diodes (NIR lc-LDs), which combine laser diode excitation with ceramic converters offering superior thermal stability and high-power endurance.
In this work, MgO:Ni2+,Cr3+ luminescent ceramics based on non-equivalent cation substitution strategy and high temperature ceramic sintering method was developed. More importantly, non-equivalent cation substitution of Mg2+ by co-doping with Cr3+ results in a high lattice distortion in [NiO6] octahedral, which breaks the parity-forbidden 3d-3d transition of Ni2+ and consequently improves its luminescence efficiency. At the same time, resonant energy transfer from Cr3+ to Ni2+ further improves the luminescence efficiency of Ni2+. The resultant MgO:N2+,Cr3+ ceramics achieve unprecedented 39.69% EQE with NIR-II emissions at 1330 nm, high thermal conductivity of 31.28 W·m-1·K-1, and excellent anti-luminescence thermal quenching of 92.11%@478K. Implemented in laser-driven devices, these ceramics enable record 214 mW output power under 21.43 W/mm2 blue laser excitation. Benefitting from the fabricated NIR-II lc-LDs based on translucent MgO:Ni2+,Cr3+ ceramics, we successfully demonstrated non-destructive imaging capabilities with spatial resolution of 5.29 lp/mm and 0.97 contrast ratio. This work provides rational design of Ni2+-activated NIR-II luminescent ceramics for next-generation laser-driven NIR-II lighting source, thereby meeting the growing demands in non-destructive detection and imaging applications.
Article Title
Laser-driven luminescent ceramic-converted near-infrared II light source for advanced imaging and detection techniques