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Light-emitting diode (LED) and organic light-emitting diode (OLED)-based displays are self-luminous display elements that convert electricity to light (electroluminescence).  Such display materials actively emit light of appropriate color(s) to create images.  OLEDs are manufactured as thin multi-layer devices, in which two electrodes (one of them is transparent) envelop the thin layers of materials that are capable to actively emit light.

LEDs and OLEDs
LEDs and OLEDs are thin layer devices that convert electricity directly into light.

Under the influence of an electric field, electrons and holes (the counterpart positive charge) injected by the electrodes travel through the organic material in opposite directions. Collision of a hole and an electron in the material between the electrodes releases energy resulting in emission of light. The nature of the materials sandwiched between the electrodes defines the actual color emitted from the device. In order to construct multi-color (full color) display devices, one must fabricate sub-millimeter dots (pixels) composed of the three basic colors, red, green, and blue (RGB signal). The combination of red, green, and blue colors allows mixing any color on demand.

OLEDs are characterized by low operating voltages and power consumption, ease of processing, robustness, wide viewing angles, and high brightness and contrast ratios, which make them compatible with portable applications.

IllustrationOne of the most widely used low-molecular-mass light emitter and the most stable electron-transporting material for OLED on the market is 8-hydroxyquinoline (Alq3). This material is currently used in Kodak-made displays utilized in viewfinders of cameras and some cellular phones.  As a material, Alq3 is not only unique by its emitting and charge-transport properties, but also low cost and offers easy processing of films. The only disadvantage of Alq3 is its unavailability in high-color purity necessary for the fabrication of full-color displays, which requires high-purity Red/Green/Blue (RGB) electroluminescent complexes to generate a high quality RGB signal. 

Recently, Dr. Pavel Anzenbacher’s group at Bowling Green State University has achieved significant progress in understanding the photophysical properties of Alq3, enabling careful tuning of the electronic properties of the ligand structure and subsequently, the Blue-Green-Red tuning in the respective OLEDs.