Hackmanite, tugtupite, and scapolite change their color from white to purple, pink, and blue, respectively, under UV irradiation, according to a team of scientists from the University of Turku.
“Color-changing minerals are inorganic natural materials, but there are also organic compounds, hydrocarbons, that can change color reversibly due to exposure to radiation,” said Professor Mika Lastusaari, a researcher in the Department of Chemistry at the University of Turku.
“Those hydrocarbons, however, can only change color only a few times before their molecular structure breaks down.”
“This is because the color change involves a drastic change in the structure, and undergoing this change repeatedly eventually breaks the molecule.”
Using a combination of experimental and computational methods, Professor Lastusaari and colleagues performed a deep analysis of the characteristics of three aluminosilicate minerals: hackmanite, tugtupite and scapolite.
“In our research, we found out for the first time that there is actually a structural change involved in the color change process,” Professor Lastusaari said.
“When the color changes, sodium atoms in the structure move relatively far away from their usual places and then return back.”
“This can be called as structural breathing and it does not destroy the structure even if it is repeated a large number of times.”
“In these color-changing minerals, all processes associated with the color change occur inside the pores of the zeolitic cage where the sodium and chlorine atoms reside,” he added.
“That is, the cage-like structure allows atomic movement inside the cage while keeping the cage itself intact.”
“This is why minerals can change color and revert back to their original color practically indefinitely,” added Sami Vuori, a doctoral candidate in the Department of Chemistry at the University of Turku.
According to the team, scapolite changes color much faster than hackmanite, whereas tugtupite’s changes are much slower.
“Based on the results of this work, we found out that the speed of the color change correlates with the distance that the sodium atoms move,” said Hannah Byron, a doctoral student in the Department of Chemistry at the University of Turku.
“These observations are important for future material development, because now we know what is required from the host structure to allow the control and tailoring of the color change properties.”
“The strength of hackmanite’s color depends on how much UV radiation it is exposed to, which means that the material can be used, for example, to determine the UV index of Sun’s radiation,” Vuori said.
“The hackmanite that will be tested on the space station will be used in a similar fashion, but this property can also be used in everyday applications.”
“We have for example already developed a mobile phone application for measuring UV radiation that can be used by anyone.”
The team’s work appears in the Proceedings of the National Academy of Sciences.