Effect of low Earth orbit radiation levels of decay characteristics of thermographic phosphors

The authors have investigated the effects of the environment outside of the Earth’s protective atmosphere on the decay characteristics of thermographic phosphor powders and phosphor composites. Phosphor thermometry is a versatile, accurate, noncontact and rapid method of thermometry that uses the luminescent properties of phosphors to measure temperature [1] This precise, remote, and instantaneous method of thermometry covers temperatures ranging from cryogenic to 1700 C and potentially beyond [2]. The temperature dependent information can be inferred by measuring the decay characteristics of the emitted signal, and/ or the decay intensity [3]. The study presented here focuses on evaluating the effect of atomic oxygen and UV radiation on the excitation / emission characteristics of La₂O₂S: Eu and Mg₃F₂GeO₄: Mn thermographic phosphors. Samples were flown on MISSE-Aegis Aerospace Inc and after a 6 month duration returned to Earth for evaluation and characterization. Post exposure tests ranged from -50 to 250 C for luminescence excited by 365 and 405 nm. It is expected that decay time should be a sensitive indicator of radiation damage. Examination and comparison of results of decay time versus temperature for both exposed and unexposed samples appears to indicate no discernible change for these characteristics within measurement uncertainty. This suggests little or no damage to the thermographic phosphors.