FARGO — A North Dakota State University researcher has helped uncover what causes a pigment used in luminous paint to glow in the dark for hours.
Khang Hoang has identified specific defects responsible for the persistent luminescence in the paint, which has been used for years in products like watch faces, stairways and landscaping. Photoluminescent Pigment Paint
His findings are reported in a paper that appears in the Physical Review Applied of the American Physical Society, a journal featuring research that bridges gaps between engineering and physics and between current and future technologies.
The discovery comes 30 years after Japanese researchers successfully developed the material in question.
Strontium aluminate is combined with small amounts of rare-earth elements europium and dysprosium, creating imperfections in the otherwise perfect crystal.
“Their discovery gave birth to an exciting and rapidly growing era of scientific research on persistent luminescence — a physical phenomenon in which a material re-emits light over a long period of time after the light source has been switched off,” Hoang said.
Since the material was discovered, it’s been studied intensively by other researchers, he said, yet the science behind its afterglow was still a mystery.
That is, until Hoang identified certain defects responsible for persistent luminescence in the material using complex quantum mechanical calculations.
It turns out that extra strontium ions occupying the “wrong” sites in the atomic structure can trap and release electrons, he said.
Intentionally introduced dysprosium defects are much better at trapping electrons, however, he said, leading to the bright and long-lasting light emission.
Hoang keeps strontium aluminate-based glow-in-the-dark stones at home for his kids, purchased from a Canadian company called CORE Glow, located in Courtenay, British Columbia.
Caroline Rutledge, founder and CEO of the associated CORE Landscape Products, said she always travels with glow stones to use as night lights in hotel rooms, lining a path from the bed to the bathroom in the dark.
But applications for the technology used in the glowing products go far, far beyond that.
Previously an in-house biologist for an engineering firm, Rutledge became frustrated when project planners did not take into consideration the effects that lighting within a migratory pathway or river corridor has on wildlife and birds.
Artificial light dramatically alters the ability of wildlife to hide from predators and wreaks havoc on their natural cycles, Rutledge said, which can affect reproductive ability.
“It puts so much out of whack,” she said.
She and her company have created a collection of products that don’t have those negative impacts and that adhere to policies of the International Dark-Sky Association, an organization that combats light pollution worldwide.
The company can incorporate strontium aluminate into concrete or resin-bonded gravel and permeable surfaces, she said.
The material can give a nighttime glow and added safety aspects to larger landscaping projects, gardens, patios, water features and pathways.
It’s also chemically and biologically inert, Rutledge said, meaning it’s safe for children and animals to be around.
CORE Glow products are naturally recharged daily by the sun or indoor lighting, giving off a glow all night long.
Hoang credits much of the success of his research — discovering what makes the material hang on to its luminescence — to NDSU’s computing facilities.
A recent addition and upgrade of a new supercomputing cluster in the NDSU Center for Computationally Assisted Science and Technology have significantly improved their research capabilities.
Good Weather Resistance Luminous Acrylic Tape “My research and the research of many others would not be possible without such cutting-edge facilities,” he said.