A joint force of international scientists from Lehigh University, West Chester University, Osaka University and the University of Amsterdam came up with a new technique, and the result could pave the way for monolithic integration for simple color tuning of a light bulb. Volkmar Dierolf, Distinguished Professor and Chair of Lehigh's Department of Physics who worked on the project confirmed this.
According to Dierolf, this new study could make it possible to tune between bright white and more comfortable warmer colors in commercial LEDs. The study is published in an article published online in ACS Photonics, and it was led by Brandon Mitchell, a graduate student in Dierolf's lab, now an assistant professor in the Department of Physics and Engineering at West Chester University in Pennsylvania.
In their demonstration, the team investigated the possibility of color tuning Gallium Nitride (GaN) - based GaN LEDs by merely changing the time sequence at which the operating current is provided to the device. Light-emitting diodes or LEDs are semiconductor devices that emit light when an electric current is passed through it. Notably, the technique is compatible with current LEDs that are at the core of commercial solid-state LED lighting.
In the active LED displays of today, when they place four individual LEDs close to each other to produce different colors, they create the different fundamental colors needed to provide the full-color spectrum.
Dierolf added that they demonstrated that they could achieve this by a single LED. They revealed that it is possible to attain red, green and blue emissions originating from just one GaN LED - a structure that uses doping with a single type of rare earth ion, Europium (Eu). They also used co-doping and energy-transfer engineering to show that all three primary colors can emit due to emission originating from two different excited states of the same Eu3+ ion (~620 nm and ~545nm) mixed with near band edge emission from GaN centered at ~430nm. When they choose the current injection conditions including injection current density and duty cycle under pulsed current injection, they can control the intensity ratios of these transitions.
The scientists achieved color-tunability in a single GaN-based LED through the manipulation of the emission properties of an atomic-type dopant.
In Mitchell's word, the central concept of this work, the simultaneous active exploitation of multiple excited states of the same dopant, is not limited to the GaN: Eu system but is more general. The presented results could open up a whole new field of tunable emission of colors from a single dopant in semiconductors, which can be reached by simple injection current tuning. Dierolf pointed out that the study may benefit those who are looking for more comfortable "warmer" white light from LEDs.
