At Georgia Tech Research Institute a new device tuned to kill biological contaminants has been created. Using specific phosphors that emit UV light via cathodoluminescence effect, the device kills tiny critters on surfaces and within.
From Georgia Tech:
Using flat panel modules that produce X-rays and ultraviolet-C (UV-C) light simultaneously, the researchers can kill anthrax spores in two to three hours without any lingering effects. The system also has the ability to kill anthrax spores hidden in places like computer keyboards without causing damage.
"This is certainly an improvement over previous techniques," said Brent Wagner, GTRI principal research scientist and director of its Phosphor Technology Center of Excellence (PTCOE). "The UV-C attacks spores on surfaces and the X-rays penetrate through materials and kill spores in cracks and crevices."
The new decontamination system resembles a coat rack with radiation modules arranged on rings at various heights that face outward to broadcast radiation throughout a room. Since the X-rays and UV-C are lethal at the flux densities used, the system operates unattended and is turned on outside the affected space.
UV-C light in the modules is produced using the optical and electrical phenomenon of cathodoluminescence. Numerous electron beams are generated by arrays of cold cathodes, each acting like the electron gun in a cathode ray tube.
"When an electron beam hits a powder phosphor, it luminesces and emits visible and/or non-visible light," explained Hisham Menkara, a senior research scientist in GTRI’s Electro-Optical Systems Laboratory.
With the Sarnoff phosphors in hand, Wagner and Menkara set off to determine the best UV-C emitting phosphor and optimize its properties for use with X-rays in SMD’s small flat panel display.
To find the best phosphor that emitted light in the UV-C region of the spectrum – wavelengths below 280 nanometers – the emission spectra of each phosphor was measured against the DNA absorption curve. This curve shows the optimal wavelengths to destroy an organism’s DNA.
After investigating many different phosphors, the researchers chose lanthanum phosphate:praseodymium (LaPO4:Pr or LAP:Pr) as the most efficient phosphor, with a power efficiency near 10 percent. Since the UV emission didn’t fall completely under the DNA absorption curve, the relative “killing efficiency” was approximately 50 percent.
In the laboratory, Menkara created the phosphor by mixing precursors lanthanum oxide, hydrogen phosphate and praseodymium fluoride (La2O3, H3PO4 and PrF3, respectively) in a glass beaker with methanol (CH3OH) and ammonium chloride (NH4Cl). Air drying the mixture in a fume hood caused the methanol to completely evaporate.
The resultant cake was crushed into a fine powder, heated in a furnace to a temperature as high as 1250 degrees Celsius for two hours and crushed again.
“To determine the best conditions for producing the highest efficiency phosphor, we tried different precursors and completed the firing under different atmospheric conditions and temperatures,” explained Menkara.
Test results showed that higher temperatures were more efficient and a capped quartz tube was the best container to hold the powder inside the furnace. Wagner and Menkara also found that adding lithium fluoride (LiF) and reducing the praseodymium concentration increased the cathodoluminescent properties of the LAP:Pr phosphor.
With the improved phosphor, laboratory tests conducted by SMD showed that the combined X-ray and UV-C decontamination system could kill anthrax spores.