Luminescent Materials:

Phosphors and Organic LEDs

Prof. Michael J. SailorDepartment of Chemistry and Biochemistry

University of California, San Diego

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

Mosquito Bay, Puerto Rico

This unique bay contains up to 720,000 non-toxic dinoflagellates per gallon of bay water.Each flash a strobe of bluish light whenagitated at night and can create enough light toread a book from.

Bacterial luciferin

Dinoflagellate luciferin has a structure similar to chlorophyll

Vargulin is found “seed shrimp"

Coelenterazine is the most common marine luciferins

LuciferinO2

Oxyluciferin +

LIGHTLuciferase

ATP

Chemistry of Bioluminescence

•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 resetthe systemTypical Luciferin Molecules

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.

top view

Green FluorescentProtein

the protein’s beta-sheets protect the chromophore from being quenched.

side view

inside, three aminoacids (serine, tyrosine, andglycine) are cyclized andoxidized to form the chromophore.

•Thin, and daylight-viewable•Rugged, yet lightweight•Power efficient•Easily custom formatted

OLEDs are of Interest to Industryand Academia because of their

Properties and Versatility

Professor Mark E.Thompson- USC

Electron transport layer

Hole transport layer

Cathode

Transparent Anode

Basic Organic Light EmittingDiode (OLED) Design

•A thin sandwich of one or more specialty polymers between twoelectrodes

•One electrode must be transparent to let the light out

•A battery voltage across the electrodes generates holes andelectrons in the respective layers which upon recombination emitenergy in the form of light.

•The color (energy) of the light depends upon the choice ofpolymer and can be tuned using well-defined organic syntheticmethods

The Appeal of Plastic Displays

FLEXIBLEFLEXIBLEADVANTAGE: Durable displays can be fashioned on novelsubstrates, including plastic, instead of glass.

DREAM PRODUCTS:•Cloth-like screens that roll up like scrolls, reducing the sizeof laptop computers.•Luminescent strips could also be sewn into clothing fordecoration or advertising.

THIN AND INEXPENSIVETHIN AND INEXPENSIVEADVANTAGE: Produced in fewer layers than LCDs, with fewermanufacturing steps. Don't need backlights.

DREAM PRODUCTS:•Devices will be very light and cheap, paving the way forvideo ''postcards'' that could record and display five-secondvideos.

SCALABLE PICTURE ELEMENTSSCALABLE PICTURE ELEMENTS

ADVANTAGE: Pixels--dots of colored light--are deposited invariable sizes and shapes.

DREAM PRODUCTS:•Giant video screens applied like wallpaper to living roomwalls.•Aircraft makers could replace heavy ceiling lights with onelong ceiling panel.

Fluorescent Lighting

Cross-section

glass

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 blueemitting phosphors that often contain Europium,

Cadmium, Lead, or Terbium activator metalsthat are toxic and/or expensive.

Ballast (current control, etc.)

A. L. Srivastava and T. J. Sommerer, Interface, Vol. 7, No. 2, (1998), 28-31.

Emission Spectrum of a typical cool, white halophosphate phosphor

(a) red emitting V2O3:Eu3+

(b) green emitting LaPO4:Ce3+, Tb3+

(c) blue emitting (Sr, Ca, Ba)5(PO4)3Cl:Eu2+

Emission Spectrum of a rare-earth phosphorused in the triphosphor blend.

A. L. Srivastava and T. J. Sommerer, Interface, vol. 7, No. 2, (1998), 28-31.

Luminescent Silicone Polymers

R Acid Luminescence*-H formic vs, pale yellow-CH3 acetic s, deep orange-CH(OH)CH3 lactic s, orange-CF3 trifluoroacetic m, deep red-m-C6H4-OH salicilic s, yellow

* Green et al, Science, 247, (1997) 1826.

(EtO)3Si(CH2)3NH2 + RCOH

=O

Si- O)3 - Si(CH2)3NHC-R + H2O + EtOH=

O(

amide

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, 7,395-398.

Photo courtesy Kathleen R. Gisser, TimothyJ. Hughes, Kodak