Nanocrystal-based phosphors with enhanced lifetime stability
- Lumisyn LLC
For many years, nanocrystals have been touted as the next generation of down-converter materials for LED lighting. This is a consequence of their high quantum efficiency, ease of spectral tuning, narrow spectral width and lack of optical scattering. However, one major drawback with nanocrystals is that they suffer from rapid oxidation, especially when used as on chip phosphors where they are subject to elevated blue LED light intensities (which catalyzes enhanced oxidation) and higher temperatures. Further exacerbating this problem is that all semiconductors form a native oxide layer of 1-2 nm thick at room temperature. Given that typical nanocrystals are on the order of 5 nm, this native oxide formation is problematical. Our approach for obtaining good long-term stability is to employ thicker nanocrystal shells which are lattice matched to the core. In order to avoid the usage of toxic compounds, our nanocrystals are free of Cd, As and Pb. The core’s material platform is InGaP while the shells were based on ZnMgSeS. Lattice-matched shelling enables thicker shells to be obtained while maintaining high efficiency, in addition to having the shells be more conformal. During the course of the project we also made an important discovery concerning the usage of novel materials in the wide bandgap shells. These materials simultaneously enabled the nanocrystals to improve in efficiency, spectral width, and long-term stability. These novel materials should also be highly impactful to a range of nanomaterial applications beyond that of solid state lighting. Regarding long-term stability testing, we were able to obtain reasonable results over hundreds of hours for nanocrystals subject to typical LED operational conditions. Though the stability results are short of that required for product placement, they are a substantial improvement over those reported in the literature. Overall, the project results showed that nm-scale shelling/encapsulation is a viable approach for enabling quality long-term stability of nanocrystals when used as on chip phosphors. Future efforts to further refine the shelling process and material composition should lead to additional improvements in nanocrystal operational lifetimes.
- Research Organization:
- Lumisyn LLC
- Sponsoring Organization:
- DOE SBIR/STTR office; USDOE Office of Science (SC)
- DOE Contract Number:
- SC0013249
- OSTI ID:
- 1561415
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-Lumisyn-13249
- Country of Publication:
- United States
- Language:
- English
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