The mineral hackmanite (or tenacious sodalite) is an amazing natural phenomenon that has long been a mystery to scientists – even though we can now engineer synthetic materials that glow in the dark more effectively than anything in nature.
Geologists first described the mineral in the 1800s, with its tendency to lighten bright pink when it is broken or placed in the dark and lost in light. Subsequent research will shorten the chemistry behind this characteristic, but a certain type of reaction has proved elusive.
Now a new study outlines how certain types of hackmanite retain some of their glow when moving from bright to dark settings. The key is the delicate interaction between the natural impurities of the mineral, determined by how it is formed.
Gaining a better understanding of how hackmanite emits white luminescence in dark conditions will help scientists develop our own synthetic materials, capable of glowing in the dark, without any power source, for example, at an emergency exit sign.
“We’ve done a lot of research with synthetic hackmanites and are able to develop materials with a significantly longer duration than natural hackmanites,” says Isabella Norbo, a material chemist at Turku University in Finland.
“However, the conditions affecting luminescence are still unclear.”
A combination of both experimental and computational data was studied to determine which concentration and balance of sulfur, potassium, titanium and iron were most important when it came to the batlow provided by Hackmanite.
In particular, titanium was found to be a really glowing element, this glow itself being driven by electron transfer.
However, the concentration of titanium alone is not sufficient to create luminescence, requiring proper mixing of other elements.
Researchers say synthetic materials can be improved and made more efficient and reliable through a variety of such studies – even if they do not match the strength of the glow that can be engineered in nature labs.
Mika Lastusari, a material chemist at the University of Turku, says, “The materials used at the moment are all synthetic and, for example, the material with the familiar green aflo is derived from an element called Glow Europium.”
“The problem with these types of materials is that the desired element can be added to them out of the luminescence. However, the properties behind them cannot be predicted.”
The study used samples of hackmanite from Greenland, Canada, Afghanistan and Pakistan, with an international team of chemists, mineralogists, geologists, physicists, statisticians and other scientists working against it.
Part of the mystery was whether some hackmanites show a glow and others don’t, but by carefully comparing different samples, the team was able to detect a combination of orange photoluminescence (turning the released absorbed photon into light), blue constant luminescence. (Emits light without heat), and purple photochromism (a form of chemical change caused by electromagnetic radiation).
It is a complex combination of natural elements and chemical reactions, but the result should be a better synthetic material that matches this type of glow. In terms of physics, it is important to know how bright the luminescence is, but also how long it lasts.
Says Lastusari, “With these results, we obtained valuable information on the conditions affecting the endocrine glands of hackmanites.
“Although, in this case, we are not able to form materials with an effective glow like synthetic materials, nature has significantly helped in the development of more effective glowing materials.”
Research has been published in Chemistry of materials.
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