Our explorations focus on two nanophotonic approaches for modifying the emission environment: controlling the photonic density of states (photonic crystals) and introducing intense localized electromagnetic fields (surface plasmonics). Both approaches require integration of emitters with dielectric, plasmonic, or photonic crystal cavities, which we accomplish through nanofabrication and epitaxial growth (photonic crystals, fabricated metallic structures), chemical synthetic routes (core-shell dielectric/metallic spheres), or a combination of nanofabricated dielectric structures and assemblies of emitters (2D photonic crystals and quantum dots, QDs).
(a) Core/shell nanoparticle geometry: (b) A cross section of the optical intensity distribution around the core/shell nanoparticle. (c,d) Internal optical intensity enhancement as a function of core radius and thickness when the size-dependent values of the metal’s dielectric functions are used. (c) gold, (d) silver shells.
Material spontaneous-emission characteristics are not solely determined by intrinsic materials properties; they can also be modified by the environment that interacts with these materials. In this research challenge, we are exploring nanophotonic approaches to tailoring these environments to enhance (or modify) spontaneous emission. We are investigating spontaneous-emission enhancement both from electroluminescent quantum wells used in solid-state lighting (SSL) as the primary originator of light, as well as from photoluminescent QDs, which could find use as a secondary source of wavelength down-converted light for SSL.
FDTD simulation results of the 10 µm mesh design with an electric dipole source plane in place of the InAs quantum. The inset shows the z-component of the electric field and depicts the surface plasmon mode at the metal/GaAs interface occurring at 945 cm-1
This is not a new field of research—nanophotonic approaches to enhanced spontaneous emission have been studied intensely for at least two decades. However, relevance to SSL—ultra-high-efficiency at visible wavelengths—pushes these approaches to extremes and architectures that are relatively unexplored. Ultra-high-efficiency requires extremely high enhancement factors attainable for example in high-Q photonic-crystal structures; whereas visible wavelengths require limited interaction with lossy metals.
Our current emphasis is experimental, but guided and augmented with simulations (e.g., finite-difference-time-domain, FDTD) as well as analytic and microscopic theory. We achieve control of photonic density of states (PDOS) through state-of-the-art photonic crystal nanofabrication. Our process localizes and enhances the electromagnetic field using plasmonic approaches (core-shell or planar).
Developing new nanophotonic architectures to accommodate these extreme constraints may lead to new insights of importance to SSL, and also to other technologies for which ultra-high efficiencies are important.
- Dr. Igal Brener (SNL) – Principal Investigator, coordinates activities, plasmonic enhancement simulations and experiments.
- Prof. Harry A. Atwater (Caltech) – Plasmonically enhanced energy transfer.
- Prof. Steve Brueck (UNM) – Plasmonics and nanofabrication.
- Dr. Willie Luk (SNL) – Quantum dots/2D photonic crystal experiments; plasmonic-enhancement models.
- Dr. S. Ken Lyo (UC Irvine) – Nanophotonic energy transfer mechanisms and calculations.
- Dr. Eric Shaner (SNL) – Experiments and simulations of plasmon coupling to quantum dots/wells.
- Dr. Ganapathi Subramania (SNL) – 3D and 2D photonic crystal experiments and theory.
Research Challenge Publications
- Lyo, S. Ken Photon-exchange energy transfer of an electron-hole plasma between quasi-two-dimensional semiconductor layers, Journal of Luminescence, 132, 3035 (2012). [10.1016/j.jlumin.2012.06.033]
- Subramania, Ganesh; Li, Qiming; Lee, Yun-Ju; Figiel, Jeffrey J. ; Wang, George T.; and Fischer, Arthur J. Gallium Nitride Based Logpile Photonic Crystal, Nano Lett., 11, 4591-4596 (2011). [10.1021/nl201867v]
- Luk, Ting Shan; Xiong, Shisheng; Chow, Weng W.; Miao, Xiaoyu; Subramania, Ganesh; Resnick, Paul J.; Fischer, Arthur J.; and Brinker, Jeffrey C. Anomalous enhanced emission from PbS quantum dots on a photonic-crystal microcavity, Journal of the Optical Society of America B: Optical Physics, 28, 1365-1373 (2011). [10.1064/JOSAB.28.001365]
- Subramania, Ganesh; Lee, Yun-Ju; and Fischer, Arthur J. Silicon-Based Near-Visible Logpile Photonic Crystal, Adv. Mater. (Weinheim, Ger.), 22, 4180 (2010). [10.1002/adma.201001965]
- Miao, Xiaoyu; Brener, Igal; and Luk, Ting Shan Nanocomposite plasmonic fluorescence emitters with core/shell configurations, J. Opt. Soc. Am. B, 27, 1561 (2010). [10.1364/JOSAB.27.001561]
- Lyo, S. Ken Energy transfer from an electron-hole plasma layer to a quantum well in semiconductor structures, Phys. Rev. B, 81, 115303 (2010). [10.1103/PhysRevB.81.115303]
- Tsao, Jeffrey Y.; Brener, Igal; Kelley, David F.; and Lyo, S. Ken Quantum-Dot-Based Solid-State Lighting With Electric-Field-Tunable Chromaticity, J. Disp. Technol., (2012). [10.1109/JDT.2012.2225407]