Executive Summary : | Near infrared (NIR) spectroscopy has advanced applications in biosensing, food analysis, medical diagnosis, night vision, health monitoring, and agriculture. Phosphor-based NIR LEDs offer a low cost, good durability, and broad and tunable emission spectra over traditional light sources. Transition metal and rare-earth ions (Cr3+, Ni2+, Yb3+, Nd3+, and Eu2+) have been substituted in inorganic materials to generate NIR emission. Cr3+ ions have unique properties, such as wide absorption and tunable emission from 700 to 1400 nm. However, a large stoke's shift of the luminous center due to energy difference between excitation and emission light can cause strong thermal effects, chromatic drift, and reduced luminous intensity. synthesis of thermally stable broad band NIR phosphors is the main challenge at this stage. Compounds with garnet structure usually possess high structural rigidity, high luminescence efficiency, and relatively higher thermal stability. The Debye temperature (θD) is a proxy for structural rigidity, and higher θD limits accessible phonon modes, leading to non radiative transitions and quenching. Gartons offer connectivity, coordination, and composition, which influence structural rigidity. Chemical unit co substitution can reduce antisite defects and increase IQE in garnet-based systems. Pauling's rule can also improve crystal rigidity by substituting with lower charge cations like Al3+. By optimizing the Debye temperature, efficient phosphors with quantum yield close to unity can be designed. The proposed work aims to synthesize garnet-based systems sr3M2Ge3O12 (M=Y, Ga) activated with Cr3+ with high quantum efficiency and thermal stability. |