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New, Efficient Nano-Phase Materials for Blue and Deep Green Light Emitting Diodes (Phase I)

Investigating Organization

Nomadics

Principal Investigator(s)

Mr. Wei Chen, wchen@nomadics.com, (405) 372-9535

Subcontractor

Oklahoma State University

Funding Source

Small Business Innovation R&D, Phase I

Award

DOE Share: $100,000

Contract Period

7/1/04 - 4/1/05

Scientists at Nomadics have invented several nanomaterials exhibiting strong emissions in blue (435 nm) and deep green (555-585 nm). These new materials will complement, and possibly replace, the existing GaN-based and InP(As) based materials for illumination and full-color displays.

Phase I will involve the demonstration of a new type of blue emission material with a high photoluminescence quantum yield (>40%), high stability and low cost that is promising for blue LEDs. It will involve the demonstration of II-VI semiconductor nanoparticle LEDs with efficient deep grain emission (555-585 nm), low power, and high stability. Phase I will also demonstrate the concept of all-inorganic semiconductor nanoparticle LEDs with much better performance in electroluminescence efficiency, brightness, stability, and longevity than organic/inorganic nanoparticle LEDs.

The application of LEDs are ubiquitous and include indicator lights, numeric displays on consumer electronic devices, flat panel displays, general illumination, biological/ biomedical imaging and detection, and bacterial disinfection.

The goal of this project is to fabricate efficient nanoparticle LEDs with emission wavelengths in the range of 555-585 nm. To meet the overall goal of fabricating deep green LEDs, this project will focus on the following objectives in Phase I:

  1. Synthesis of silica-coated CdTe, CdSe, and CdSe/CdS solid nanoparticles with emission wavelengths in the range of 555-585 nm and photoluminescence quantum efficiency greater than 50%.

  2. Demonstration of efficiency enhancement and lifetime improvement by PLD fabrication of nanoparticle/PPV LEDs in high vacuum.

  3. Demonstration of high-efficiency electroluminescence and good stability from all-inorganic nanoparticle LEDs by sandwiching nanoparticle monolayers between p-type (SiC, ZnTe) and n-type (Si) semiconductor layers. All-inorganic nanoparticle LEDs should exhibit low operation power and voltage and high longevity.

  4. Improvement of recipes for making blue nanoparticles with narrow-size distribution and high (40%) efficiency. Successful accomplishment of these objectives will serve as proof-of-principle and will warrant continuation of the research into Phase II with a focus on demonstrating viable nanoparticle LEDs with external quantum efficiency of 25-30%, brightness of 2000 cd/cm2, and lifetime of 5000 hours.

At this point, we have successfully made nanoparticle with deep green emission with high efficiency (Figure 1) and have observed electroluminescence from our nanoparticle LEDs. Light emitting diode performance is affected by the thickness of the hole and electron transport layers. By optimizing the thickness of these layers, we have successfully confined the carriers within the nanoparticle emitting layer and observed strong luminescence from the nanoparticles.