Ionizing radiation poses a significant challenge for Earth-based defense applications as well as human and/or robotic space missions. Practical sensors based on luminescence will depend heavily upon research investigating the resistance of these materials to ionizing radiation and the ability to anneal or self-heal from damage caused by such radiation. In 1951, Birks and Black showed experimentally that the luminescent efficiency of anthracene bombarded by alphas varies with total fluence (N) as (I/I<sub>0</sub>) = 1/(1 + AN), where I is the luminescence yield, I<sub>0</sub> is the initial yield, and A is a constant. The half brightness (N<sub>1/2</sub>) is defined as the fluence that reduce the emission light yield to half and is equal to is the inverse of A. Broser and Kallmann developed a similar relationship to the Birks and Black equation for inorganic phosphors irradiated using alpha particles. From 1990 to the present, we found that the Birks and Black relation describes the reduction in light emission yield for every tested luminescent material except lead phosphate glass due to proton irradiation. These results indicate that radiation produced quenching centers compete with emission for absorbed energy. The purpose of this paper is to present results from research completed in this area over the last few years. Particular emphasis will be placed on recent measurements made on new materials such as europium tetrakis dibenzoylmethide triethylammonium (EuD<sub>4</sub>TEA). Results have shown that EuD<sub>4</sub>TEA with its relatively small N<sub>1/2</sub> might be a good candidate for use as a personal proton fluence sensor.
The desire to explore the Moon and Mars by 2030 makes cost effective and low mass health monitoring sensors
essential for spacecraft development. Parameters such as impact, temperature, and radiation fluence need to be measured
in order to determine the health of a human occupied vehicle. A phosphor-based sensor offers one good approach to
develop a robust health monitoring system. The authors have spent the last few years evaluating physical characteristics
of zinc sulfide (ZnS) phosphors. These materials emit triboluminescence (TL) which is fluorescence produced as a result
of an impact. Currently, two ZnS materials have been tested for impact response for velocities from 1 m/s to 6 km/s.
These materials have also been calibrated for use as temperature sensors from room temperature to 350 °C. Finally, any
sensor that is intended to function in space must be characterized for response to ionizing radiation. Research to date
has included irradiating ZnS with 3 MeV protons and 20 keV electrons, which are likely components of the space
radiation environment. Results have shown that that the fluorescence emission intensity decreases with radiation
fluence. However, radiation induced damage can be annealed at small fluence levels. This annealing not only increased
light intensity of the exposed sample from excitation but also TL excitation as well.
Triboluminescence (TL) is the emission of light due to crystal fracture and has been known for centuries. One of the most common examples of TL is the flash created from chewing wintergreen Lifesavers. Since 2003, the authors have been measuring triboluminescent properties of phosphors, of which zinc sulfide doped with manganese (ZnS:Mn) is an example. Preliminary results indicate that impact velocities greater than 0.5 m/s produce measurable TL from ZnS:Mn. To extend this research, the investigation of the emission spectrum was chosen. This differs from using filtered photodetectors in that the spectral composition of fluorescence can be ascertained. Previous research has utilized a variety of schemes that include scratching, crushing, and grinding to generate TL. In our case, the material is activated by a short duration interaction of a dropped mass and a small number of luminescence centers. This research provides a basis for the characterization and selection of materials for future spacecraft impact detection schemes.