Sandia uses quantum dot phosphors in white LEDs
The quantum dots strongly absorb light in the near-UV range and re-emit visible light with a color determined by both their size and surface chemistry. This provides two additional ways to tune the optical properties in addition to chemical composition of the quantum dot material itself.
Conventional phosphors have poor absorption in the near-UV region, although a great deal of research is going on to identify new, more suitable, phosphor materials. Also, the optical properties of conventional bulk phosphor powders are determined solely by the phosphor’s chemical composition.
The nanometer-size quantum dots are synthesized in a solvent containing soap-like molecules called surfactants as stabilizers.
During encapsulation, the dots are attached to the “backbone” of the encapsulating polymer. This prevents the dots from clumping together (agglomerating), which would cause them to lose their light-emitting properties. The result is an increase in efficiency from 10-20% to 60%.
In the next year the researchers will increase the concentration of the quantum dots in the encapsulant to obtain further increases in light output while extending the understanding of quantum dot electronic interactions at high concentrations.
The work is part of an internally funded research project, and has also received funding from the DOE Office of Building Technologies for a collaborative project with Lumileds Lighting.
