Researchers from the Stanford Institute for Materials and Energy Sciences have shown that materials science can be a game-changer. They discovered that magnificent colors shine forth from films of amorphous copper complex when humans rub, twist, bend or snap them. This novel mechanoluminescence (ML) phenomenon contradicts long-held beliefs of the structural characteristics required to induce light emissions from materials. The study was led by a team under the direction of Dr. Ayumu Karimata. They have now reported their results in the journal Chemical Science.
In this study, we only investigate thin, crystal-free films produced from heteroleptic Cu complexes and well-established luminophores. To get started, the researchers looked at different ways to test for mechanoluminescence. To study the fundamental principles of external mechanical stimulation inhibiting light emissions, they applied contact-separation and friction techniques. Their result indicates that the direct mechanical actions produce microscopic electric fields inside the materials. These fields can heat the material and nearby gas to the point that they emit highly energetic visible light.
Understanding Mechanoluminescence
Mechanoluminescence is the spectacle of materials emitting light in response to mechanical stress. It was long thought that this exciting process depended almost entirely on the existence of crystalline polyhedral structures. The new study reveals a thrilling find. Non-crystalline amorphous materials can exhibit this property, unencumbered by the restrictions associated with crystalline structures.
Dr. Ayumu Karimata noted, “Traditionally, chemists have thought crystal fracture an essential step in generating mechanoluminescence.” Conducted and led by researchers at Columbia Engineering, this fundamental study reverses that paradigm by showing that amorphous solids can produce permanent luminescence with non-destructive, non-thermal mechanical stimuli.
Professor Julia Khusnutdinova elaborated on the limitations of crystal-based mechanoluminescent materials: “Mechanical stimulation of crystals causes fractures. As the crystals are damaged and break down in size, they also start to lose their ML properties, which vastly restricts their application.” This surprising insight highlights the promise of novel amorphous materials for exciting future technology.
Implications for Next-Generation Materials
The significance of this study goes well beyond the laboratory. These mechanoluminescent films are being made flexible for the first time. These films open up thrilling, new opportunities to develop unique, sustainable materials for a range of applications. Whether in displays and sensors or safety and protective equipment, the applications that these new crystal-free films can augment are virtually limitless.
The researchers are currently investigating the properties of these new amorphous copper complex films. They look forward to new innovations that will lead to greater functionality and broader applications. The prospect of producing illuminative materials without needing to base them on intricate crystal forms is a huge leap forward in material science.
Historical Context and Future Directions
Mechanoluminescence has a long and interesting past going back to the 1600s. Francis Bacon performed an experiment in which he scraped and broke hard sugar in the dark, producing luminous flashes of light. This historical context serves to underscore the deeply-rooted interest in discovering how mechanical forces can create light.
Returning to their work, the research team’s approach marks a new turn on the concept of the scroll and reinforces the need to explore experimental material forms. They’re making progress, too, digging deeper with these shapeshifting films. Their aim is to lead the development of new next-generation materials that have the potential to drive disruptive new technology.