Plasmon-enhanced photoluminescence of silicon quantum dots: simulation and experiment

The enhancement of photoluminescence emission from silicon quantum dots in the near field of cylindrical silver particles has been calculated using finite integration techniques. This computational method permitted a quantitative examination of the plasmon resonance frequencies and locally enhanced fields surrounding coupled arrays of silver particles having arbitrary shapes and finite sizes. We have studied Ag nanoparticles with diameters in the 50-300 nanometer range and array pitches in the range of 50-800 nm, near a plane of optical emitters spaced 10-40 nm from the arrays. The calculated and experimental plasmon resonance frequencies and luminescence enhancements are in good agreement. In the tens-of-nanometers size regime, for the geometries under investigation, two competing factors affect the photoluminescence enhancement; on one hand, larger field enhancements, which produce greater emission enhancements, exist around smaller silver particles. However, as the spacing of such particles is decreased to attain higher surface coverages, the interparticle coupling draws the enhanced field into the lateral gaps between particles and away from the emitters, leading to a decrease in the plasmonic emission enhancement. The computations have thus revealed the limitations of using arbitrarily dense arrays of plasmonic metal particles to enhance the emission from coplanar arrays of dipole-like emitters. For such a geometry, a maximum sixfold net emission enhancement is predicted for the situation in which the plasmonic layer is composed of 50 nm diameter Ag particles in an array having a 300 nm pitch.

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