Glow in the dark 3D printer filament for FDM 3D printing has been around for a while now, mostly as a novelty so that people can make fun glow in the dark prints. Glow in the dark materials haven’t really been seen in SLA 3D printing, however. But in a study entitled “Three-dimensional printing of hybrid organic/inorganic composites with long persistence luminescence,” researchers develop a material for SLA 3D printing that glows. The applications for such a material are many – not just toys and crafts but night-glowing signs and indicators.

In order to create the material, the researchers incorporated inorganic long persistent phosphors, or LPPs, into organic resin. LPPs can absorb and store photoelectrons under excitation, then release light for minutes, hours or even days afterwards. They are often used in concealed lighting for decoration, safety displays, or equipment nameplates, as well as in advanced scientific fields such as clinical medicine, biomedicine, life sciences, energy and environmental engineering.

Glowing materials for FDM 3D printing are created by melting polymers, mixing them with LPPs and then extruding them as a filament. The researchers in this study, however, wanted to create glowing objects with the precision that only SLA can offer. They also point out that creating parts through SLA with resin slurry containing LPPs is more economically and energy efficient than extruding LPPs into filaments.

The researchers created resins with different types of LPPs, resulting in different glowing colors – red, green, and blue – and differing lengths of luminescence. The resin slurries they created are not sensitive to oxygen, according to the researchers, so they do not need to be stored or used in an inert or nitrogen atmosphere – 3D printing can take place in an ambient atmosphere. They then 3D printed samples from the resins and tested their luminescent properties.

“Then we recorded the intensity change in peak position of 653 nm, 520 nm and 470 nm over time after turning off the excitation light because the decay time plays a vital role in LPPs,” the researchers explain. “Theoretically, white afterglow resin samples can be obtained by co-doping of currently available LPPs with red, green and blue emissions. However, LPPs with different colors seldom have very similar decay times.”

That meant that some of the samples glowed for more than two hours after the light was turned off, while others glowed for only a recorded 2,000 seconds.

“It has to be noted here that there is a six-fold difference in the decay time,” the researchers continue. “Therefore, it is difficult to fabricate such a composite sample that retains the white persistent luminescence, because composite samples containing different LPPs particles change colors over time after the cease of the excitation.”

More complex parts were then 3D printed: a dog, a hollow birdcage and a gear wheel, to demonstrate SLA’s ability to print in fine detail. The parts showed good quality and uniform color, confirming that the LPP particles were homogeneously distributed. After being charged with a xenon lamp for five minutes, the parts glowed for a long time, and they also demonstrated the ability to be charged and discharged repeatedly without degradation of luminescent properties.

“The resin has a negative effect on the afterglow brightness of long persistent phosphors, but printed parts has considerable luminescence intensity and attractive afterglow decay time,” the researchers state. “Therefore, the slurry doped with LPPs can be used for exquisite crafts, customized toys and night indicators with high precision.”

The materials’ thermal and temperature sensing properties were also tested, and it was confirmed that one of the composites in particular had a large temperature coefficient between 40°C and 70°C, meaning that it could potentially be used in optical thermometers. Other suggested applications include bioimaging and solar cells.

Authors of the paper include Rongping Ni, Bin Qian, Chang Liu, Xiaofeng Liu, and Jianrong Qiu.

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