Optical properties and scattering distribution of thermographic phosphors

The optical properties and scattering distribution of thermographic phosphors have been demonstrated using a combined experimental and numerical method. ZnO:Zn and BaMgAl₁₀O₁₇:Eu²⁺ (BAM) are two types of widely used phosphors due to their stable physical properties and high-temperature sensitivities. To study their inter-phosphor light transfer, the angular scattering distribution and light propagation of these two phosphor suspensions was measured using a spectro-goniometric system. A collision-based Monte Carlo ray-tracing model was developed to extract their optical properties, including extinction coefficient, scattering albedo, asymmetry factors, and scattering fraction. With the void fraction around 0.98, the extinction coefficient of ZnO:Zn was determined to be 4.719, while that of F grade BAM and N grade BAM were 11.584 and 9.777, respectively. In addition, BAM had a higher scattering fraction (α = 0.99) than ZnO:Zn (α = 0.88). Due to the higher values of extinction coefficient and scattering fraction, BAM demonstrated more significant scattering than ZnO:Zn. Light transmission through phosphor suspensions was predicted along the direction of the light path. For ZnO:Zn, 70% of flux was scattered when the distance increases to 0.5, while for BAM, the distance was 0.15. Furthermore, with the same mass loading, smaller particle sizes can promote scattering and reduce the amount of light transmitted through phosphor suspensions.