Research Challenge 5: Enhanced Spontaneous Emission
- (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) Au, d) Ag shells.
Our explorations focus on two nanophotonic approaches for modifying the emission environment: control of photonic density of states (photonic crystals) and introduction of 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 QDs).
The spontaneous emission characteristics of materials are not solely determined by intrinsic materials properties, but 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 quantum dots, which could find use as a secondary source of wavelength down-converted light for SSL.
- Finite-difference time-domain (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 solid-state lighting – 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) as well as analytic and microscopic theory. We achieve control of photonic density of states (PDOS) through state-of-the-art nanofabrication of photonic crystals. Localization and enhancement of electromagnetic fields is realized using plasmonic approaches (core-shell or planar).
Developing new nanophotonic architectures to accommodate these extreme constraints may lead to new insights of importance to solid-state lighting, 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
Passmore, Brian S.; Adams, David C.; Ribaudo, Troy; Wasserman, Daniel; Lyon, Stephen; Chow, Weng W.; and Shaner, Eric A. Observation of Rabi Splitting from Surface-plasmon Coupled Conduction-state Transitions in Electrically-excited InAs Quantum Dots, Nano Letters, 11, 338 (2011). [10.1021/nl102412h]
Subramania, Ganesh; Li, Qiming; Lee, Yun-Ju; Figiel, Jeffrey J. ; Wang, George T.; and Fischer, Arthur J. Gallium Nitride Based Logpile Photonic Crystal, Nano Letters, 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]
Shelton, David J.; Brener, Igal; Ginn, James C.; Sinclair, Michael B.; Peters, David W.; Coffey, Kevin R.; and Boreman, Glenn D. Strong Coupling between Nanoscale Metamaterials and Phonons, Nano Letters,11, 2104-2108 (2011). [10.1021/nl200689z]
Miao, Xiaoyu; Brener, Igal; and Luk, Ting Shan Nanocomposite plasmonic fluorescence emitters with core/shell configurations, Journal of the Optical Society of America B, 27, 1561 (2010). [10.1364/JOSAB.27.001561]
Subramania, Ganesh; Lee, Yun-Ju; and Fischer, Arthur J. Silicon-Based Near-Visible Logpile Photonic Crystal, Advanced Materials (Weinheim, Ger.), 22, 4180 (2010). [10.1002/adma.201001965]
Lyo, S. Ken Energy transfer from an electron-hole plasma layer to a quantum well in semiconductor structures, Physical Review B, 81, 115303 (2010). [10.1103/PhysRevB.81.115303]
Schubert, Martin F.; and Schubert, E. Fred Effect of heterointerface polarization charges and well depth upon capture and dwell time for electrons and holes above GaInN/GaN quantum wells, Applied Physics Letters, 96, 131102 (2010). [10.1063/1.3373610]