The composition and structure of luminescent materials play a crucial role in determining their photochemical properties, such as emission spectra, quantum yield, and lifetime. Here's how:1. Emission spectra: The emission spectra of luminescent materials depend on the energy levels of their constituent atoms or molecules and the transitions between these levels. The composition of the material, including the types of atoms or molecules and their arrangement, determines the energy levels and the resulting emission spectra. For example, organic luminescent materials like conjugated polymers have different emission spectra than inorganic materials like quantum dots or phosphors due to differences in their molecular structures and energy levels.2. Quantum yield: Quantum yield is the ratio of the number of emitted photons to the number of absorbed photons. The composition and structure of luminescent materials affect their quantum yield by influencing factors such as the probability of radiative transitions emission of photons and non-radiative transitions energy dissipation through other processes . For instance, materials with a higher degree of structural order and fewer defects typically exhibit higher quantum yields, as defects can act as non-radiative recombination centers.3. Lifetime: The lifetime of luminescent materials is the time it takes for the material's luminescence intensity to decrease to a certain fraction of its initial value. The composition and structure of the material can affect the lifetime by influencing the rates of radiative and non-radiative transitions. Materials with fewer defects and impurities generally have longer lifetimes, as these defects can act as non-radiative recombination centers, leading to faster decay of luminescence. Additionally, the type of excited state e.g., singlet or triplet and the energy gap between the excited and ground states can also impact the lifetime.In summary, the composition and structure of luminescent materials are critical factors that determine their photochemical properties, including emission spectra, quantum yield, and lifetime. By controlling the composition and structure, researchers can tailor these properties for specific applications, such as lighting, displays, and sensing.