[INVITED] Near-infrared phosphors and their full potential: A review on practical applications and future perspectives

Near-infrared (NIR) phosphors are enticing photoluminescent materials with applications in light-emitting diodes for spectroscopy. These phosphors have two types of emissions: Type I has a Gaussian curve, whereas Type II is similar to a plateau. Both emissions have industrial uses, but uncertain remains regarding which type is ideal. In this review, we compare two distinct NIR phosphors with Type I and Type II emissions in terms of their structure, crystal field, and emission profile and then provide our perspective on what the ideal emission must be.