(Invited) Discovery of Static Electricity Induced Luminescence (SEL) Sensing Material Toward Visualizing Invisible Static Electricity Distribution

Static electricity is an extremely familiar phenomenon. Most people have probably felt sparks (electrostatic discharge) when a charged object (e.g., a charged human finger) is brought close to a metal. In terms of safety measures, it is known as a source of ignition and explosion. In the semiconductor industry, electrostatic destruction and malfunction of miniaturized electronic elements, and more recently, in relation to fuel consumption and operability of lightweight electric mobility, it is attracting more and more attention. On the other hand, static electricity is still a mystery and elusive when looking at static electricity evaluation. Conventional electrostatic sensors are difficult to use to measure static electricity on objects with uneven surfaces, in moving objects, and in changing measurement environments. Above all, the lack of intuitive means to understand static electricity, such as seeing it with the eyes or taking pictures of it with a camera, has made it a difficult problem to solve. This is also the reason why there are so many industrial needs. In contrast, the authors, who had been studying mechanoluminescent (ML) ceramic materials, later realized that they were mistaken, but it did not seem unusual for functional materials to produce color change or luminescence if there is an inflow of electric charge. We systematically searched for known materials (fluorescence, EL, afterglow, stress luminescence, chemiluminescence, etc.) in which charge is involved in luminescence, and found that a certain type of SrAl 2 O 4 : Eu 2+ ( ceramic particles) emits light in response to weak electricity such as ions and charged particles in the air, called static electricity The electrostatic luminescence (SEL) spectra of SrAl 2 O4:Eu 2+ (ceramic particles) are the world's first findings of its function as a static electricity induced luminescence (SEL) material. The electrostatic luminescence spectrum has a peak at 510 nm, similar to photoluminescence, and is derived from Eu2+ (4f 7 -4f 6 5d 1 ). It was also found that the electrostatic luminescence is affected by the crystalline state, even if the chemical formula is the same. When a film of electrostatically luminescent SrAl2O4: Eu2+ prepared by solid-phase synthesis and dispersed in resin was irradiated with corona discharge from an electrostatic generator gun, green luminescence was observed and spread radially. When the surface potential distribution was measured after the observation, the charged area and the luminescent area coincided. Although the experiment was conducted in a dark place for reproducibility, the luminosity was so high that it was visible even with room lights on. It was also found that electrostatic sparks when a person's finger is brought close can be visualized even before the discharge (Figure). Currently, electrostatic luminescent ceramic materials of various types and luminescent colors have been developed, increasing the diversity of electrostatic luminescence. In this presentation, we will explain novel SEL material and the sensors toward visualizing invisible static electricity generation and distribution. １．K. Kikunaga and N. Terasaki: “Demonstration of Static Electricity Induced Luminescence”, Scientific Reports , 12 , 8524 (2022). Open access https://www.nature.com/articles/s41598-022-12704-5 Figure 1