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Silver-Copper Alloy Nanoparticles for Metal Enhanced Luminescence

Sanchari Chowdhury, Chemical and Biomedical Engineering, University of South Florida, ENB 118, 4202 E Fowler Avenue, Tampa, FL 33620, Venkat Bhethanabotla, Department of Chemical Engineering, University of South Florida, ENB 118, 4202 E. Fowler Ave., Tampa, FL 33620, and Rajan Sen, Civil Engineering, University of South Florida, ENB 118, 4202 E Fowler Avenue, Tampa, FL 33620.

Luminescence based measurements and devices are currently widely used methods in different fields such as biology, chemistry, materials science and medicine.  Strong luminescence intensity is one of the most important desired properties for luminophores for these applications.  At the vicinity of conducting metallic nanoparticles such as those of silver and gold, the emission intensity of luminophores is known to be significantly influenced.  Surface plasmon resonance (SPR) wavelength, one of the most important properties of nanostructures, dictates the choice of materials to be used for luminescence enhancement.  Tam et al.(1) found that the enhancement is optimal when the plasmon resonance of the nanoparticles is tuned to the emission wavelength of the low quantum yield luminophores. Recently, some theoretical and experimental studies have suggested that luminescence enhancement is largest when emission wavelength is slightly red-shifted from the plasmon resonance(2, 3).  One can expect that by tuning the position of the SPR peak of the nanoparticles over a wide range of wavelengths, metal enhanced luminescence can be extended for a wide range of luminophores.  Metal alloys offer additional degrees of freedom for tuning their optical properties by altering atomic composition and atomic arrangement.  This motivates us to study alloy nanostructured platforms for metal enhanced luminescence (MEL). 

Due to their interesting optical properties, we have chosen to study silver-copper alloy nanoparticles(4) for MEL application.  SPR wavelengths of these Ag-Cu nanoparticles were tuned in the visible and near infrared region by changing annealing temperature.  We observed strong emission enhancement of luminophores (141.48+/-19.20 times for Alexa Fluor 488 and 23.91 +/-12.37 times for Alexa Fluor 594) at the vicinity of Ag-Cu nanoparticles when SPR spectrum was tuned to produce maximum spectral overlap.  This study suggests that as SPR spectrum of Ag-Cu alloy nanoparticles can easily be tailored, this platform can be effectively used to enhance luminescence of different luminophores.  This finding opens new avenue for the utilization of metal alloy nanoparticles in MEL applications.

Reference:

1.         F. Tam, G. P. Goodrich, B. R. Johnson, N. J. Halas, Nano Lett. 7, 496-501 (2007).

2.         Y. Chen, K. Munechika, D. S. Ginger, Nano Lett. 7, 690-696 (2007).

3.         M. Thomas, J.-J. Greffet, R. Carminati, Appl. Phys. Lett. 85, 3863-3865 (2004).

4.         M. Hirai, A. Kumar, J. Appl. Phys. 100, 014309 (2006).