Luminescent Materials: Phosphors and Organic LEDs Prof. Michael J. Sailor Department of Chemistry and Biochemistry University of California, San Diego

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1 Luminescent Materials: Phosphors and Organic LEDs Prof. Michael J. Sailor Department of Chemistry and Biochemistry University of California, San Diego

2 Outline I. Luminescence in Nature -Bioluminescence -Green Fluorescent Protein II. Organic Light-Emitting Diodes III. Phosphors - Fluorescent Lighting - Luminescent Silicate Polymers IV. Electoluminescent Porous Silicon

3 Mosquito Bay, Puerto Rico This unique bay contains up to 720,000 nontoxic dinoflagellates per gallon of bay water. Each flash a strobe of bluish light when agitated at night and can create enough light to read a book from.

4 Chemistry of Bioluminescence Luciferin ATP O 2 Luciferase Oxyluciferin + LIGHT Two chemicals are required for luminescence The light-producing compound is called a luciferin The catalyst is called a luciferase Energy, here shown as ATP, must be provided to reset the system Typical Luciferin Molecules Bacterial luciferin Vargulin is found seed shrimp" Dinoflagellate luciferin has a structure similar to chlorophyll Coelenterazine is the most common marine luciferins

5 Green Fluorescent Protein (GFP) - A naturally fluorescent material that occurs in a jellyfish in the Puget Sound. - Here the DNA code for this protein has been injected into bacteria which then makes GFP. - The bacteria is then grown on an agar plate, and exposed to blue light. Dr. Brian Reid, Yale School of Medicine.

6 Green Fluorescent Protein the protein s betasheets protect the chromophore from being quenched. side view inside, three amino acids (serine, tyrosine, and glycine) are cyclized and oxidized to form the chromophore. top view

7 OLEDs are of Interest to Industry and Academia because of their Properties and Versatility Professor Mark E. Thompson- USC Thin, and daylight-viewable Rugged, yet lightweight Power efficient Easily custom formatted

8 Basic Organic Light Emitting Diode (OLED) Design Cathode Electron transport layer Hole transport layer Transparent Anode A thin sandwich of one or more specialty polymers between two electrodes One electrode must be transparent to let the light out A battery voltage across the electrodes generates holes and electrons in the respective layers which upon recombination emit energy in the form of light. The color (energy) of the light depends upon the choice of polymer and can be tuned using well-defined organic synthetic methods

9 The Appeal of Plastic Displays FLEXIBLE ADVANTAGE: Durable displays can be fashioned on novel substrates, including plastic, instead of glass. DREAM PRODUCTS: Cloth-like screens that roll up like scrolls, reducing the size of laptop computers. Luminescent strips could also be sewn into clothing for decoration or advertising. THIN AND INEXPENSIVE ADVANTAGE: Produced in fewer layers than LCDs, with fewer manufacturing steps. Don't need backlights. DREAM PRODUCTS: Devices will be very light and cheap, paving the way for video ''postcards'' that could record and display five-second videos. SCALABLE PICTURE ELEMENTS ADVANTAGE: Pixels--dots of colored light--are deposited in variable sizes and shapes. DREAM PRODUCTS: Giant video screens applied like wallpaper to living room walls. Aircraft makers could replace heavy ceiling lights with one long ceiling panel.

10 Fluorescent Lighting Ballast (current control, etc.) glass Cross-section phosphors plasma - The plasma generates UV light, mercury vapor is the most efficient, but xenon is safer. - White light is generated from red, green, and blue emitting phosphors that often contain Europium, Cadmium, Lead, or Terbium activator metals that are toxic and/or expensive.

11 Emission Spectrum of a typical cool, white halophosphate phosphor A. L. Srivastava and T. J. Sommerer, Interface, Vol. 7, No. 2, (1998),

12 Emission Spectrum of a rare-earth phosphor used in the triphosphor blend. (a) red emitting V 2 O 3 :Eu 3+ (b) green emitting LaPO 4 :Ce 3+, Tb 3+ (c) blue emitting (Sr, Ca, Ba) 5 (PO 4 ) 3 Cl:Eu 2+ A. L. Srivastava and T. J. Sommerer, Interface, vol. 7, No. 2, (1998),

13 Luminescent Silicone Polymers =O (EtO) 3 Si(CH 2 ) 3 NH 2 + RCOH ( =O Si- O) 3 - Si(CH 2 ) 3 NHC-R + H2O + EtOH amide R Acid Luminescence* -H formic vs, pale yellow -CH 3 acetic s, deep orange -CH(OH)CH 3 lactic s, orange -CF 3 trifluoroacetic m, deep red -m-c 6 H 4 -OH salicilic s, yellow * Green et al, Science, 247, (1997) 1826.

14 Organic Light-Emitting Diodes Electroluminescent Properties of Self- Assembled Polymer Thin Films. Jing Tian, Chung-Chih Wu, Mark E. Thompson, James C. Sturm, Richard A. Register, Advanced Materials, 1995, 7, Photo courtesy Kathleen R. Gisser, Timothy J. Hughes, Kodak