September 2013

Towards Truly White LED Lighting

Adding platinum atoms tunes the color of emitted light.

Click to enlarge photo. Enlarge Photo

Image courtesy of Z.V. Vardeny

The visible light emission from a polymer film containing platinum atoms has been tuned by adjusting the spacing of the platinum atoms in the polymer chain. The resulting fluorescence and phosphorescence emission bands combine to produce “white light” when the polymer is excited with ultraviolet light. The polymer emits a combination of broad-spectrum violet and yellow that appears “white” to the human eye.

The Science

Discovered that the insertion of platinum atoms into the chain-like backbone of certain polymers can be used to tune the energy levels of the material and enables light emission from the polymer that appears ‘white’ to the human eye.

The Impact

The ability to tune a family of organic polymers to emit light of different colors is a key step toward a new kind of organic light-emitting diode, or OLED, that can emit truly white light while improving efficiency and lowering cost for the LED-based light bulbs and displays of the future.

Summary

Existing white OLEDs—like those used in current cell phones and smart phones—are not truly white. These displays use a combination of organic polymers that emit different colors arranged in pixels of red, green and blue, combined to make white light. Research led by the University of Utah has succeeded in synthesizing and characterizing light-emitting polymers containing platinum atoms within the polymer chain. These polymers show both intrinsic fluorescence and phosphorescence emission bands that naturally combine to appear ‘white’ to the human eye. Adding a heavy atom such as platinum into the chain structure of the polymer alters the energy levels of the material and enables light emission (yellow to orange) via a process called phosphorescence from a normally inaccessible “triplet” energetic state of the polymer. When combined with the normally observed fluorescence emission (violet to blue) from the “singlet” energetic state of the polymer, the platinum-containing polymer exhibits a combined luminescence which can be tuned by varying the amount of platinum atoms in the polymer chains. Platinum atoms, because of their higher atomic mass, facilitate the formation of “triplet” states via a process called spin-orbit coupling. The length of the polymer chain between the platinum atoms determines the rate of ultrafast conversion of “singlet” state to “triplet” state and hence the amounts of fluorescent and phosphorescent light emitted. Having demonstrated that multiple colors can be simultaneously emitted from one polymer with UV light stimulation, the next step in the development of simpler, more efficient white OLEDs is to demonstrate the polymer’s light emission characteristics when stimulated by the injection of electrical charges.

Contact

Valy Vardeny
University of Utah
val@physics.utah.edu

Funding

Basic Research: DOE, Office of Science, Basic Energy Sciences, the National Science Foundation (electroabsorption (EA) studies) and the Laboratory Directed Research and Development program at Los Alamos National Laboratory (quantum chemical calculations); C.-X.S. was supported by NSFC grant program of China and Fundamental Research Funds for Central Universities.

Publications

C. –X. Sheng, S. Singh, A Gambetta, T. Drori, M. Tong, S. Tretiak, and V. Vardeny; “Ultrafast Intersystem-crossing in Platinum-containing π-Conjugated Polymers with Tunable Spin-Orbit Coupling”, Scientific Reports, 2013, 3, 2653. [DOI: 10.1038/srep02653]

Related Links

http://unews.utah.edu/news_releases/toward-a-truly-white-organic-led/External link

Highlight Categories

Program: BES, MSE

Performer/Facility: University, DOE Laboratory

Additional: Technology Impact, Collaborations, NNSA, International Collaboration

Last modified: 1/3/2014 9:42:40 AM