Detection of low-velocity-impact triboluminescent emissions

Abstract

Over the last decade, research has shown that triboluminescence (TL) can be used as the active element for impact sensors. TL is defined as the emission of light produced by the fracture of materials. For the last decade, extensive experience has been gained in characterizing TL and has been successfully characterized from low speed impacts. For the most part, zinc sulfide and europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA) compounds have been used as sample materials since both emit strong TL. A simple and low-cost “drop tower” was designed, tested, and utilized to measure important triboluminescent properties such as light yield, decay time, and emission spectra from low-velocity impacts. This apparatus was successfully used to test and compare the triboluminescent emission from over 100 different materials and is currently being used to evaluate a selection of synthesized derivatives. Results show that the EuD4TEA sample doped with DBP has the largest tested triboluminescent yield for any of the tested materials. The EuD4TEA doped with DBP had nearly six times the triboluminescent yield compared to the baseline 7.5µm ZnS:Mn. The EuD4TEA powder synthesized at AAMU was found to emit more than twice as much TL compared to the sample prepared by Sandia National Laboratories in California. The average triboluminescent yield from the AAMU synthesized EuD4TEA was slightly more than two times larger than what was measured for the baseline 7.5lm ZnS:Mn powder. However, EuD4TEA appears to be more easily damaged than ZnS:Mn. The triboluminescent yield for EuD4TEA decreases by a factor of three from drops one to five. Conversely, the yield only decreases about 10% over the same number of drops and various amounts used for ZnS:Mn. Results also show that the 19.8lm ZnS:Mn emitted the most TL of any of the tested inorganic materials. It is likely that the method used to prepare the 19.8µm ZnS:Mn in terms of grain size, trap concentration, and dopant concentration was responsible for the increased triboluminescent yield. It appears that on average, ZnS:Mn, Cu has a larger triboluminescent yield ratio compared to ZnS:Mn. Finally, no TL was observed when the steel ball bearing was dropped on the 5nm sized ZnS:Mn powder synthesized at CINT. It is likely that the small 5nm ZnS:Mn particles were trapped in surface imperfections and were not subject to sufficient force to produce TL. This chapter discusses these findings in detail.