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The residual glow of the mineral hackmanite (or tenebrescent sodalite) is a fascinating natural phenomenon that has long been a mystery to scientists, although we are now able to design synthetic materials that glow in the dark more effectively than anything else. in nature.
Geologists first described the mineral in the 1800s, who were intrigued by its tendency to glow slightly a bright pink hue when broken or placed in the dark and lose it in the light. Later research would narrow the chemistry behind this feature, but the precise nature of the reaction has proved elusive.
Now a new study outlines exactly how certain types of hackmanite retain some of their luster as they transition from bright to dark settings. The key is the delicate interplay between the mineral’s natural impurities, determined by how it is formed.
Gaining a better understanding of how hackmanite can emit white luminescence in dark conditions will further help scientists develop our synthetic materials that can glow in the dark without any power source, such as on an emergency exit sign, for example. .
“We did a lot of research with synthetic hackmanites and were able to develop a material with a significantly longer glow than natural hackmanite,” says materials chemist Isabella Norrbo of the University of Turku in Finland.
“However, the conditions affecting the luminescence have so far been unclear.”
A combination of both experimental and computational data was investigated to determine that the concentrations and balance of sulfur, potassium, titanium, and iron were most important when it came to the glow emitted by hackmanite.
In particular, titanium was found to be the actual glowing element, with the glow itself being fueled by electron transfer.
However, titanium concentrations alone are not sufficient to create luminescence, with the right mix of other elements also required.
Researchers say synthetic materials can be improved and made more efficient and reliable through these kinds of studies, even if nature cannot match the strength of the glows that can be designed in the laboratory.
“The materials used at the moment are all synthetic and, for example, the material with the familiar residual green glow gets its glow from an element called europium,” says materials chemist Mika Lastusaari of the University of Turku.
“The difficulty with this type of material is that even if the desired element that emits luminescence can be added to them, their glow properties cannot be predicted.”
Hackmanite samples from Greenland, Canada, Afghanistan and Pakistan were used in the study, with an international team of chemists, mineralogists, geologists, physicists, statisticians and other scientists involved in working out exactly what was happening with the hackmanite glow.
Part of the mystery was why some hackmanites show a glow and others don’t, but through careful comparison of the different samples, the team was able to pinpoint the required mix of orange photoluminescence (which turns absorbed photons into light), persistent blue luminescence. (which emits light without heating) and purple photochromism (a form of chemical transformation caused by electromagnetic radiation).
It’s a complex mix of natural elements and chemical reactions, but the result should be better synthetics that can match these types of glows. In terms of materials science, it is important not only how bright the luminescence is, but also how long it lasts.
“With these results, we have gained valuable insight into the conditions that affect the afterglow of hackmanites,” says Lastusaari.
“Although nature, in this case, was not able to form a material with an effective glow as in synthetic materials, nature has contributed significantly to the development of increasingly effective luminous materials.”
The research was published in Chemistry of materials.
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