Shortwave Infrared Luminescence of Tetravalent Chromium and Divalent Nickel: Phosphor Design Principles and Applications

Shortwave infrared radiations (SWIR, 900–1700 nm) emitting inorganic luminescent materials are key components for multiple applications, which range from optical communication and anticounterfeiting purposes to chemical and medical diagnosis. The blue light excitable SWIR phosphors activated with the transition metal ions Cr4+/Ni2+ are considered prospective light sources for an upcoming compact modern device using phosphor converter technology. In this review, the crystal field theory and Tanabe-Sugano diagram are briefly discussed to understand the splitting of energy levels and the concurrent effect. Several possible strategies to achieve and enhance the luminescence efficiency of Cr4+/Ni2+ SWIR emission are disclosed as is the reported chemical system. Finally, the domains for the potential practical application of SWIR phosphors are introduced. This review will provide information on the recent advances and the luminescence mechanism of Cr4+/Ni2+-activated SWIR phosphors and will also assist researchers in developing next-generation SWIR phosphors and exploring new applications.