Ultra-broadband near-infrared emission of Cr3+-containing oxy-fluoride glass-ceramics

Abstract

Broadband near-infrared (NIR) light sources cover unique optical wavelengths and are valuable in the fields of bioimaging and photodynamic therapy, night vision lighting and security monitoring. NIR phosphor converted light-emitting diode (NIR pc-LED) devices have attractive features such as tunable emission peak, low cost of production, compact in sizes and high luminous efficiency. However, heat accumulation during operation due to poor thermal conductivity of the organic resin used in packaging often causes serious reduction in luminous efficiency and accelerated degradation of the device. In present work, we developed a Cr3+-doped transparent CaF2-based oxy-fluoride glass-ceramic (GC) that showed a broadband emission of 700∼1400 nm under 470 nm excitation. The emission peaked at ∼880 nm, the full-width at half maximum was about ∼297 nm, and the photoluminescence quantum yield reached ∼31.19 %. The emission was derived from the electronic transition of Cr3+ ions from the 4T2(F) to 4A2(F). Through structural analysis and numerical simulation, we showed that during the heat treatment process, Cr3+ ions were enriched into the CaF2 crystal phase and replaced the Ca2+ in the GC host with occupied the center position of the polyhedrons, which provided a weak crystal field and led to NIR emission. We built NIR pc-LED devices using optimized GC and commercial blue LED chips, and we demonstrated the application of this NIR pc-LED in night-vision lighting. Our approaches to prepare simple and stable inorganic NIR luminous materials sealed in bulk in a transparent CaF2-based oxy-fluoride GC and to construct pc-LED devices could provide new concept to the field and have practical implications to applications in related fields.