Like a coin, every crime has two sides—the truth and the lie. However, just like in coin toss games, you cannot use probability mathematics in crime scene investigation to play flip games without solid proof. When examining the evidence in a real-world criminal case, one must make sure that unfairness is completely ruled out. The fight for justice is based on a rigorous assessment of evidence, which necessitates technologies that reveal hidden details and view the unknown. In recent years, luminous materials (phosphors) known as up-conversion phosphors have emerged as viable tools for forensic investigations, providing distinct benefits in scene interpretation and evidence collecting. This chapter digs into the fascinating potential of upconversion phosphors for forensic applications, investigating their principles, functions, and promising future developments. Unlike traditional phosphors, which absorb high-energy light and release lower-energy photons (down conversion), upconversion phosphors use elegant physics (anti stokes shifting) to convert low-energy near-infrared (NIR) radiation into higher-energy visible or ultraviolet (UV) light. This extraordinary phenomenon results from consecutive photon absorption in specially developed lanthanide-doped materials. As NIR light stimulates the lanthanide ions, they undergo several energy level transitions, eventually emitting higher-energy light. In present chapter, details of upconversion phosphor for various forensic based applications, current research and potential phosphor for the same is discussed in detail and some of the valuable applications are given: (1) Latent fingerprint detection (2) Tracing Evidences (3) Security markers (4) Anticounterfeiting. While upconversion phosphors have intriguing promise, some problems remain, which developers can overcome. These issues include: sensitivity to various surfaces, reduced toxicity, improved biocompatibility, selectivity to specific analytes, economic cost, availability, and practicality. The chapter also covers all of these obstacles and provides scientific papers that offer ways to mitigate them. Along with-it futuristic application is also discussed.