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tech.com
Simplified Color Tuning of LED Bulbs
Bethlehem, PA — A new technique, the result of an international collabo- ration of scientists from Lehigh University, West Chester University, Osaka University, and the Univer - sity of Amsterdam, could pave the way for monolithic integration for simple color tuning of a light bulb. “This work could make it possi-
ble to tune between bright white and more comfortable warmer colors in commercial LEDS,” says Volkmar Dierolf, Distinguished Professor and chair of Lehigh University’s depart- ment of physics. The team demonstrated the
possibility of color tuning gallium nitride (GaN) based GaN LEDs sim- ply by changing the time sequence at which the operation current is pro- vided to the device. LEDs are semi- conductor devices that emit light when an electric current is passed through them. Notably, the tech- nique is compatible with current LEDs, which are at the core of com- mercial solid state LED lighting. In today’s active LED displays,
different colors are produced by three to four individual LEDs, which are placed close to each other and create
the different fundamental colors need- ed to produce the full color spectrum.
“We demonstrate that this can be achieved by a single LED,” says
ing, we show that all three primary colors can emit, due to emission orig- inating from two different excited states of the same Eu3+ ion (~620 and ~545 nm) mixed with near-band- edge emission from GaN centered at ~430 nm. The intensity ratios of these transitions can be controlled by choosing the current injection condi- tions, such as injection current densi- ty and duty cycle under pulsed cur- rent injection.” In other words, the team
achieved color-tunability in a single GaN-based LED through the manip- ulation of the emission properties of an atomic-type dopant. “The main idea of this work —
The top row is a GaN:Eu LED, which can be tuned from red-yellow
due to red and green light mixing from different Eu states. The mid- dle and bottom rows are of a GaN:Eu LED with additionally added Si/Mg, which adds blue emission.
Dierolf. “We show that it is possible to attain red, green and blue emis- sions originating from just one GaN LED structure that uses doping with a single type of rare-earth ion, Europium (Eu). Using intentional co- doping and energy-transfer engineer-
the simultaneous activation exploita- tion of multiple excited states of the same dopant — is not limited to the Gan-Eu system, but is more general,” says Brandon Mitchell, former grad- uate student in Dierolf’s lab and now an assistant professor in the depart- ment of physics and engineering at West Chester University. “The pre- sented results could open up a whole new field of tunable emission of col- ors from a single dopant in semicon- ductors, which can be reached by simple injection current tuning.” “This could pave the way for
monolithic integration for simple color tuning of a light bulb,” adds Dierolf. “It would also be beneficial for micro-LED displays, since it allows for a higher density of pixels.” Web:
www.lehigh.edu r
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